MacFormat 1995 January/macformat-020.iso/Shareware City/Applications/Alpha.5.96 folder/Help/Perl Commands

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================================================================================

 Note: To install the Perl mode and menu, select the menu item
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================================================================================

NAME
     perl - Practical Extraction and Report Language

SYNOPSIS
     perl [options] filename args

DESCRIPTION
     Perl is an interpreted language optimized for scanning arbi-
     trary  text  files,  extracting  information from those text
     files, and printing reports based on that information.  It's
     also  a good language for many system management tasks.  The
     language is intended to be practical  (easy  to  use,  effi-
     cient,  complete)  rather  than  beautiful  (tiny,  elegant,
     minimal).  It combines (in  the  author's  opinion,  anyway)
     some  of the best features of C, sed, awk, and sh, so people
     familiar with those languages should have little  difficulty
     with  it.  (Language historians will also note some vestiges
     of csh, Pascal,  and  even  BASIC-PLUS.)  Expression  syntax
     corresponds  quite  closely  to C expression syntax.  Unlike
     most Unix utilities, perl does  not  arbitrarily  limit  the
     size  of your data--if you've got the memory, perl can slurp
     in your whole file as a  single  string.   Recursion  is  of
     unlimited  depth.   And  the hash tables used by associative
     arrays grow as necessary to  prevent  degraded  performance.
     Perl  uses sophisticated pattern matching techniques to scan
     large amounts of data very quickly.  Although optimized  for
     scanning  text, perl can also deal with binary data, and can
     make dbm files look like associative arrays  (where  dbm  is
     available).   Setuid  perl scripts are safer than C programs
     through a dataflow tracing  mechanism  which  prevents  many
     stupid  security  holes.   If  you have a problem that would
     ordinarily use sed or awk or sh, but it exceeds their  capa-
     bilities  or must run a little faster, and you don't want to
     write the silly thing in C, then perl may be for you.  There
     are  also  translators to turn your sed and awk scripts into
     perl scripts.  OK, enough hype.

     Upon startup, perl looks for your script in one of the  fol-
     lowing places:

     1.  Specified line by line via -e switches  on  the  command
         line.

     2.  Contained in the file specified by the first filename on
         the  command line.  (Note that systems supporting the #!
         notation invoke interpreters this way.)

     3.  Passed in implicitly  via  standard  input.   This  only
         works  if there are no filename arguments--to pass argu-
         ments to a stdin script you must explicitly specify a  -
         for the script name.

     After locating your script, perl compiles it to an  internal
     form.   If  the  script is syntactically correct, it is exe-
     cuted.

     Options

     Note: on first reading this section may not make much  sense
     to you.  It's here at the front for easy reference.

     A single-character option may be combined with the following
     option, if any.  This is particularly useful when invoking a
     script using the #! construct which only  allows  one  argu-
     ment.  Example:

          #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
          ...

     Options include:

     -0digits
          specifies the record separator ($/) as an octal number.
          If  there  are  no  digits,  the  null character is the
          separator.  Other switches may precede  or  follow  the
          digits.   For  example,  if  you have a version of find
          which can print filenames terminated by the null  char-
          acter, you can say this:

              find . -name '*.bak' -print0 | perl -n0e unlink

          The special value 00 will cause Perl to slurp files  in
          paragraph  mode.   The  value  0777  will cause Perl to
          slurp files whole since there  is  no  legal  character
          with that value.

     -a   turns on autosplit mode when used with a -n or -p.   An
          implicit  split  command to the @F array is done as the
          first thing inside the implicit while loop produced  by
          the -n or -p.

               perl -ane 'print pop(@F), "\n";'

          is equivalent to

               while (<>) {
                    @F = split(' ');
                    print pop(@F), "\n";
               }

     -c   causes perl to check the syntax of the script and  then
          exit without executing it.

     -d   runs the script under the perl debugger.  See the  sec-
          tion on Debugging.

     -Dnumber
          sets debugging flags.  To watch how  it  executes  your
          script,  use  -D14.   (This  only works if debugging is
          compiled into your perl.) Another nice value is -D1024,
          which  lists  your  compiled  syntax  tree.   And -D512
          displays compiled regular expressions.

     -e commandline
          may be used to enter one line of script.   Multiple  -e
          commands  may be given to build up a multi-line script.
          If -e is  given,  perl  will  not  look  for  a  script
          filename in the argument list.

     -iextension
          specifies that files processed by the <> construct  are
          to  be  edited  in-place.  It does this by renaming the
          input file, opening the output file by the  same  name,
          and selecting that output file as the default for print
          statements.  The extension, if supplied,  is  added  to
          the  name of the old file to make a backup copy.  If no
          extension is supplied, no backup is made.  Saying "perl
          -p  -i.bak  -e "s/foo/bar/;" ... " is the same as using
          the script:

               #!/usr/bin/perl -pi.bak
               s/foo/bar/;

          which is equivalent to

               #!/usr/bin/perl
               while (<>) {
                    if ($ARGV ne $oldargv) {
                         rename($ARGV, $ARGV . '.bak');
                         open(ARGVOUT, ">$ARGV");
                         select(ARGVOUT);
                         $oldargv = $ARGV;
                    }
                    s/foo/bar/;
               }
               continue {
                   print;     # this prints to original filename
               }
               select(STDOUT);

          except that the -i form doesn't need to  compare  $ARGV
          to  $oldargv to know when the filename has changed.  It
          does, however, use ARGVOUT for the selected filehandle.
          Note  that  STDOUT  is  restored  as the default output
          filehandle after the loop.

          You can use eof to locate the end of each  input  file,
          in  case you want to append to each file, or reset line
          numbering (see example under eof).

     -Idirectory
          may be used in  conjunction  with  -P  to  tell  the  C
          preprocessor  where  to  look  for  include  files.  By
          default /usr/include and /usr/lib/perl are searched.

     -loctnum
          enables automatic line-ending processing.  It  has  two
          effects:  first, it automatically chops the line termi-
          nator when used with -n or -p , and second, it  assigns
          $\ to have the value of octnum so that any print state-
          ments will have that line terminator added back on.  If
          octnum  is omitted, sets $\ to the current value of $/.
          For instance, to trim lines to 80 columns:

               perl -lpe 'substr($_, 80) = ""'

          Note that the assignment $\  =  $/  is  done  when  the
          switch  is processed, so the input record separator can
          be different than the output record separator if the -l
          switch is followed by a -0 switch:

               gnufind / -print0 | perl -ln0e 'print "found $_" if -p'

          This sets $\ to newline and then sets $/  to  the  null
          character.

     -n   causes perl to assume the following  loop  around  your
          script,  which makes it iterate over filename arguments
          somewhat like "sed -n" or awk:

               while (<>) {
                    ...       # your script goes here
               }

          Note that the lines are not printed by default.  See -p
          to  have  lines  printed.   Here is an efficient way to
          delete all files older than a week:

               find . -mtime +7 -print | perl -nle 'unlink;'

          This is faster than using  the  -exec  switch  of  find
          because  you  don't  have  to  start a process on every
          filename found.

     -p   causes perl to assume the following  loop  around  your
          script,  which makes it iterate over filename arguments
          somewhat like sed:

               while (<>) {
                    ...       # your script goes here
               } continue {
                    print;
               }

          Note that the  lines  are  printed  automatically.   To
          suppress  printing use the -n switch.  A -p overrides a
          -n switch.

     -P   causes your script to be run through the C preprocessor
          before  compilation  by perl.  (Since both comments and
          cpp directives begin with the # character,  you  should
          avoid  starting  comments  with any words recognized by
          the C preprocessor such as "if", "else" or "define".)

     -s   enables some rudimentary switch parsing for switches on
          the  command  line after the script name but before any
          filename arguments (or before a --).  Any switch  found
          there  is removed from @ARGV and sets the corresponding
          variable in the  perl  script.   The  following  script
          prints "true" if and only if the script is invoked with
          a -xyz switch.

               #!/usr/bin/perl -s
               if ($xyz) { print "true\n"; }

     -S   makes perl use the PATH environment variable to  search
          for  the  script  (unless the name of the script starts
          with a slash).  Typically this is used  to  emulate  #!
          startup  on machines that don't support #!, in the fol-
          lowing manner:

               #!/usr/bin/perl
               eval "exec /usr/bin/perl -S $0 $*"
                    if $running_under_some_shell;

          The system ignores the first line and feeds the  script
          to  /bin/sh,  which proceeds to try to execute the perl
          script as a  shell  script.   The  shell  executes  the
          second  line as a normal shell command, and thus starts
          up the perl interpreter.  On some  systems  $0  doesn't
          always  contain the full pathname, so the -S tells perl
          to search for the  script  if  necessary.   After  perl
          locates  the  script,  it  parses the lines and ignores
          them because the variable $running_under_some_shell  is
          never  true.   A  better  construct  than  $*  would be
          ${1+"$@"}, which handles embedded spaces  and  such  in
          the  filenames, but doesn't work if the script is being
          interpreted by csh.  In order to  start  up  sh  rather
          than  csh, some systems may have to replace the #! line
          with a line containing just a colon, which will be pol-
          itely  ignored  by  perl.   Other systems can't control
          that, and need a totally devious  construct  that  will
          work  under any of csh, sh or perl, such as the follow-
          ing:

               eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
               & eval 'exec /usr/bin/perl -S $0 $argv:q'
                    if 0;

     -u   causes perl to dump core after compiling  your  script.
          You  can  then  take this core dump and turn it into an
          executable file by using the undump program  (not  sup-
          plied).   This  speeds  startup  at the expense of some
          disk space (which you can  minimize  by  stripping  the
          executable).   (Still, a "hello world" executable comes
          out to about 200K on my machine.) If you are  going  to
          run your executable as a set-id program then you should
          probably compile it using taintperl rather than  normal
          perl.   If you want to execute a portion of your script
          before dumping, use the dump operator  instead.   Note:
          availability of undump is platform specific and may not
          be available for a specific port of perl.

     -U   allows perl to do  unsafe  operations.   Currently  the
          only  "unsafe"  operations  are the unlinking of direc-
          tories while running as superuser, and  running  setuid
          programs with fatal taint checks turned into warnings.

     -v   prints the version and patchlevel of your perl  execut-
          able.

     -w   prints warnings about identifiers  that  are  mentioned
          only  once,  and  scalar variables that are used before
          being set.  Also warns about redefined subroutines, and
          references  to  undefined  filehandles  or  filehandles
          opened readonly that you are attempting  to  write  on.
          Also  warns you if you use == on values that don't look
          like numbers, and if your subroutines recurse more than
          100 deep.

     -xdirectory
          tells perl that the script is embedded  in  a  message.
          Leading  garbage will be discarded until the first line
          that starts with #! and  contains  the  string  "perl".
          Any  meaningful  switches  on that line will be applied
          (but only one group of switches, as with normal #! pro-
          cessing).   If a directory name is specified, Perl will
          switch to that directory  before  running  the  script.
          The -x switch only controls the the disposal of leading
          garbage.  The script must be terminated with __END__ if
          there is trailing garbage to be ignored (the script can
          process any or all of the trailing garbage via the DATA
          filehandle if desired).

     Data Types and Objects

     Perl has three data types: scalars, arrays of  scalars,  and
     associative arrays of scalars.  Normal arrays are indexed by
     number, and associative arrays by string.

     The interpretation of operations and values  in  perl  some-
     times  depends on the requirements of the context around the
     operation or value.  There are three major contexts: string,
     numeric  and  array.  Certain operations return array values
     in contexts wanting an array, and scalar  values  otherwise.
     (If this is true of an operation it will be mentioned in the
     documentation for that operation.) Operations  which  return
     scalars  don't  care  whether  the  context is looking for a
     string or a number, but  scalar  variables  and  values  are
     interpreted as strings or numbers as appropriate to the con-
     text.  A scalar is interpreted as TRUE in the boolean  sense
     if  it  is  not  the null string or 0.  Booleans returned by
     operators are 1 for true and 0 or '' (the null  string)  for
     false.

     There are actually two varieties of null string: defined and
     undefined.   Undefined  null strings are returned when there
     is no real value for something, such as when  there  was  an
     error, or at end of file, or when you refer to an uninitial-
     ized variable or element of an  array.   An  undefined  null
     string  may become defined the first time you access it, but
     prior to that you can use the defined() operator  to  deter-
     mine whether the value is defined or not.

     References to scalar variables always begin with  '$',  even
     when referring to a scalar that is part of an array.  Thus:

         $days           # a simple scalar variable
         $days[28]       # 29th element of array @days
         $days{'Feb'}    # one value from an associative array
         $#days          # last index of array @days

     but entire arrays or array slices are denoted by '@':

         @days           # ($days[0], $days[1],... $days[n])
         @days[3,4,5]    # same as @days[3..5]
         @days{'a','c'}  # same as ($days{'a'},$days{'c'})

     and entire associative arrays are denoted by '%':

         %days           # (key1, val1, key2, val2 ...)

     Any of these eight constructs may serve as an  lvalue,  that
     is,  may be assigned to.  (It also turns out that an assign-
     ment is itself an lvalue in certain  contexts--see  examples
     under  s, tr and chop.) Assignment to a scalar evaluates the
     righthand side in a scalar context, while assignment  to  an
     array  or  array  slice  evaluates  the righthand side in an
     array context.

     You may  find  the  length  of  array  @days  by  evaluating
     "$#days",  as in csh.  (Actually, it's not the length of the
     array, it's the subscript of the last element,  since  there
     is  (ordinarily) a 0th element.) Assigning to $#days changes
     the length of the array.  Shortening an array by this method
     does  not actually destroy any values.  Lengthening an array
     that was previously shortened recovers the values that  were
     in  those elements.  You can also gain some measure of effi-
     ciency by preextending an array that is going  to  get  big.
     (You  can  also  extend  an array by assigning to an element
     that is off the end of the array.  This differs from assign-
     ing to $#whatever in that intervening values are set to null
     rather than recovered.) You can truncate an  array  down  to
     nothing  by assigning the null list () to it.  The following
     are exactly equivalent

          @whatever = ();
          $#whatever = $[ - 1;

     If you evaluate an array in a scalar context, it returns the
     length of the array.  The following is always true:

          scalar(@whatever) == $#whatever - $[ + 1;

     If you evaluate an associative array in a scalar context, it
     returns  a value which is true if and only if the array con-
     tains any elements.  (If there are any elements,  the  value
     returned  is a string consisting of the number of used buck-
     ets and the number of  allocated  buckets,  separated  by  a
     slash.)

     Multi-dimensional arrays are not directly supported, but see
     the  discussion of the $; variable later for a means of emu-
     lating multiple subscripts with an associative  array.   You
     could  also  write  a subroutine to turn multiple subscripts
     into a single subscript.

     Every data type has its own  namespace.   You  can,  without
     fear  of  conflict, use the same name for a scalar variable,
     an array, an associative array, a filehandle,  a  subroutine
     name,  and/or  a label.  Since variable and array references
     always start with '$', '@', or  '%',  the  "reserved"  words
     aren't  in  fact  reserved  with  respect to variable names.

     (They ARE reserved with respect to labels  and  filehandles,
     however,  which  don't  have  an  initial special character.
     Hint:  you  could  say   open(LOG,'logfile')   rather   than
     open(log,'logfile').    Using   uppercase  filehandles  also
     improves readability and protects  you  from  conflict  with
     future  reserved  words.)  Case IS significant--"FOO", "Foo"
     and "foo" are all different names.  Names which start with a
     letter may also contain digits and underscores.  Names which
     do not start with a letter are  limited  to  one  character,
     e.g.  "$%" or "$$".  (Most of the one character names have a
     predefined significance to perl.  More later.)

     Numeric literals are specified in any of the usual  floating
     point or integer formats:

         12345
         12345.67
         .23E-10
         0xffff     # hex
         0377  # octal

     String literals are delimited by  either  single  or  double
     quotes.   They  work  much  like shell quotes: double-quoted
     string literals are subject to backslash and  variable  sub-
     stitution;  single-quoted strings are not (except for \' and
     \\).  The usual backslash rules apply for making  characters
     such  as  newline,  tab,  etc.,  as well as some more exotic
     forms:

          \t        tab
          \n        newline
          \r        return
          \f        form feed
          \b        backspace
          \a        alarm (bell)
          \e        escape
          \033      octal char
          \x1b      hex char
          \c[       control char
          \l        lowercase next char
          \u        uppercase next char
          \L        lowercase till \E
          \U        uppercase till \E
          \E        end case modification

     You can also embed newlines directly in your  strings,  i.e.
     they  can  end on a different line than they begin.  This is
     nice, but if you forget your trailing quote, the error  will
     not be reported until perl finds another line containing the
     quote character, which may be much further on in the script.
     Variable  substitution  inside  strings is limited to scalar
     variables, normal array values, and array slices.  (In other
     words,  identifiers  beginning  with  $ or @, followed by an
     optional bracketed expression as a subscript.) The following
     code segment prints out "The price is $100."

         $Price = '$100';               # not interpreted
         print "The price is $Price.\n";# interpreted

     Note that you can put curly brackets around  the  identifier
     to  delimit it from following alphanumerics.  Also note that
     a single quoted string must be separated  from  a  preceding
     word  by a space, since single quote is a valid character in
     an identifier (see Packages).

     Two  special  literals  are  __LINE__  and  __FILE__,  which
     represent the current line number and filename at that point
     in your program.  They may only be used as separate  tokens;
     they  will  not  be interpolated into strings.  In addition,
     the token __END__ may be used to indicate the logical end of
     the  script  before  the  actual end of file.  Any following
     text is ignored (but may be read via the  DATA  filehandle).
     The  two  control  characters  ^D  and  ^Z  are synonyms for
     __END__.

     A word that doesn't have any  other  interpretation  in  the
     grammar  will  be  treated as if it had single quotes around
     it.  For this purpose, a word consists only of  alphanumeric
     characters  and underline, and must start with an alphabetic
     character.  As with filehandles and labels, a bare word that
     consists  entirely  of lowercase letters risks conflict with
     future reserved words, and if you use the  -w  switch,  Perl
     will warn you about any such words.

     Array values are interpolated into double-quoted strings  by
     joining  all  the  elements  of the array with the delimiter
     specified in the $" variable, space by default.   (Since  in
     versions  of  perl  prior  to  3.0 the @ character was not a
     metacharacter in double-quoted strings, the interpolation of
     @array,   $array[EXPR],   @array[LIST],   $array{EXPR},   or
     @array{LIST} only happens if array is  referenced  elsewhere
     in   the  program  or  is  predefined.)  The  following  are
     equivalent:

          $temp = join($",@ARGV);
          system "echo $temp";

          system "echo @ARGV";

     Within search patterns (which  also  undergo  double-quotish
     substitution)  there  is a bad ambiguity:  Is /$foo[bar]/ to
     be interpreted as /${foo}[bar]/ (where [bar] is a  character
     class for the regular expression) or as /${foo[bar]}/ (where
     [bar] is the subscript to  array  @foo)?   If  @foo  doesn't
     otherwise  exist, then it's obviously a character class.  If
     @foo exists, perl takes a good guess  about  [bar],  and  is
     almost  always  right.  If it does guess wrong, or if you're
     just plain paranoid, you can force the  correct  interpreta-
     tion with curly brackets as above.

     A line-oriented form of quoting is based on the shell  here-
     is syntax.  Following a << you specify a string to terminate
     the quoted material, and all  lines  following  the  current
     line  down  to  the  terminating string are the value of the
     item.  The terminating string may be either an identifier (a
     word),  or  some quoted text.  If quoted, the type of quotes
     you use determines the treatment of the  text,  just  as  in
     regular  quoting.   An unquoted identifier works like double
     quotes.  There must be no space between the << and the iden-
     tifier.   (If  you  put a space it will be treated as a null
     identifier, which is valid,  and  matches  the  first  blank
     line--see  Merry  Christmas  example below.) The terminating
     string must appear by itself (unquoted and with no surround-
     ing whitespace) on the terminating line.

          print <<EOF;        # same as above
     The price is $Price.
     EOF

          print <<"EOF";      # same as above
     The price is $Price.
     EOF

          print << x 10;      # null identifier is delimiter
     Merry Christmas!

          print <<`EOC`;      # execute commands
     echo hi there
     echo lo there
     EOC

          print <<foo, <<bar; # you can stack them
     I said foo.
     foo
     I said bar.
     bar

     Array literals are denoted by separating  individual  values
     by commas, and enclosing the list in parentheses:

          (LIST)

     In a context not requiring an array value, the value of  the
     array literal is the value of the final element, as in the C
     comma operator.  For example,

         @foo = ('cc', '-E', $bar);

     assigns the entire array value to array foo, but

         $foo = ('cc', '-E', $bar);

     assigns the value of variable bar  to  variable  foo.   Note
     that the value of an actual array in a scalar context is the
     length of the array; the following assigns to $foo the value
     3:

         @foo = ('cc', '-E', $bar);
         $foo = @foo;         # $foo gets 3

     You  may  have  an  optional  comma   before   the   closing
     parenthesis of an array literal, so that you can say:

         @foo = (
          1,
          2,
          3,
         );

     When a LIST is  evaluated,  each  element  of  the  list  is
     evaluated in an array context, and the resulting array value
     is interpolated into LIST just as if each individual element
     were a member of LIST.  Thus arrays lose their identity in a
     LIST--the list

          (@foo,@bar,&SomeSub)

     contains all the elements of @foo followed by all  the  ele-
     ments  of @bar, followed by all the elements returned by the
     subroutine named SomeSub.

     A list value may also be subscripted like  a  normal  array.
     Examples:

          $time = (stat($file))[8];     # stat returns array value
          $digit = ('a','b','c','d','e','f')[$digit-10];
          return (pop(@foo),pop(@foo))[0];

     Array lists may be assigned to if and only if  each  element
     of the list is an lvalue:

         ($a, $b, $c) = (1, 2, 3);

         ($map{'red'}, $map{'blue'}, $map{'green'}) = (0x00f, 0x0f0, 0xf00);

     The final element may be an array or an associative array:

         ($a, $b, @rest) = split;
         local($a, $b, %rest) = @_;

     You can actually put an array anywhere in the list, but  the
     first  array  in  the  list will soak up all the values, and
     anything after it will get a null value.  This may be useful
     in a local().

     An associative array literal contains pairs of values to  be
     interpreted as a key and a value:

         # same as map assignment above
         %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);

     Array assignment in a scalar context returns the  number  of
     elements produced by the expression on the right side of the
     assignment:

          $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2

     There are several other pseudo-literals that you should know
     about.    If  a  string  is  enclosed  by  backticks  (grave
     accents), it first undergoes variable substitution just like
     a  double  quoted  string.  It is then interpreted as a com-
     mand, and the output of that command is  the  value  of  the
     pseudo-literal,  like  in  a  shell.  In a scalar context, a
     single string consisting of all the output is returned.   In
     an  array  context,  an array of values is returned, one for
     each line of output.  (You can set $/  to  use  a  different
     line  terminator.)  The  command  is  executed each time the
     pseudo-literal is evaluated.  The status value of  the  com-
     mand  is  returned  in  $?  (see  Predefined  Names  for the
     interpretation of $?).  Unlike in  csh,  no  translation  is
     done  on  the return data--newlines remain newlines.  Unlike
     in any of the shells, single quotes  do  not  hide  variable
     names  in  the  command  from  interpretation.   To pass a $
     through to the shell you need to hide it with a backslash.

     Evaluating a filehandle in angle brackets  yields  the  next
     line  from  that file (newline included, so it's never false
     until EOF, at which time an undefined  value  is  returned).
     Ordinarily  you  must  assign  that value to a variable, but
     there is one situation where an  automatic  assignment  hap-
     pens.   If  (and only if) the input symbol is the only thing
     inside the  conditional  of  a  while  loop,  the  value  is
     automatically assigned to the variable "$_".  (This may seem
     like an odd thing to you, but you'll use  the  construct  in
     almost  every  perl script you write.) Anyway, the following
     lines are equivalent to each other:

         while ($_ = <STDIN>) { print; }
         while (<STDIN>) { print; }
         for (;<STDIN>;) { print; }
         print while $_ = <STDIN>;
         print while <STDIN>;

     The filehandles STDIN, STDOUT  and  STDERR  are  predefined.
     (The  filehandles  stdin,  stdout  and stderr will also work
     except in packages, where they would be interpreted as local
     identifiers  rather than global.) Additional filehandles may
     be created with the open function.

     If a <FILEHANDLE> is used in a context that is  looking  for
     an  array,  an  array  consisting  of all the input lines is
     returned, one line per array element.  It's easy to  make  a
     LARGE data space this way, so use with care.

     The null filehandle <> is special and can be used to emulate
     the  behavior  of  sed  and awk.  Input from <> comes either
     from standard input, or from each file listed on the command
     line.   Here's how it works: the first time <> is evaluated,
     the ARGV array is checked, and if it is  null,  $ARGV[0]  is
     set to '-', which when opened gives you standard input.  The
     ARGV array is then processed as a list  of  filenames.   The
     loop

          while (<>) {
               ...            # code for each line
          }

     is equivalent to

          unshift(@ARGV, '-') if $#ARGV < $[;
          while ($ARGV = shift) {
               open(ARGV, $ARGV);
               while (<ARGV>) {
                    ...       # code for each line
               }
          }

     except that it isn't as cumbersome to say.  It  really  does
     shift  array ARGV and put the current filename into variable
     ARGV.  It also uses filehandle  ARGV  internally.   You  can
     modify  @ARGV  before  the first <> as long as you leave the
     first filename at the beginning of the array.  Line  numbers
     ($.)  continue as if the input was one big happy file.  (But
     see example under eof for how to reset line numbers on  each
     file.)

     If you want to set @ARGV to your own list of files, go right
     ahead.   If  you want to pass switches into your script, you
     can put a loop on the front like this:

          while ($_ = $ARGV[0], /^-/) {
               shift;
              last if /^--$/;
               /^-D(.*)/ && ($debug = $1);
               /^-v/ && $verbose++;
               ...       # other switches
          }
          while (<>) {
               ...       # code for each line
          }

     The <> symbol will return FALSE only once.  If you  call  it
     again  after  this it will assume you are processing another
     @ARGV list, and if you haven't set @ARGV,  will  input  from
     STDIN.

     If the string inside the angle brackets is a reference to  a
     scalar  variable  (e.g. <$foo>), then that variable contains
     the name of the filehandle to input from.

     If the string inside angle brackets is not a filehandle,  it
     is  interpreted  as  a  filename  pattern to be globbed, and
     either an array of filenames or the  next  filename  in  the
     list  is  returned,  depending  on  context.  One level of $
     interpretation is done  first,  but  you  can't  say  <$foo>
     because  that's  an  indirect filehandle as explained in the
     previous paragraph.  You  could  insert  curly  brackets  to
     force interpretation as a filename glob: <${foo}>.  Example:

          while (<*.c>) {
               chmod 0644, $_;
          }

     is equivalent to

          open(foo, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
          while (<foo>) {
               chop;
               chmod 0644, $_;
          }

     In fact, it's currently implemented that way.  (Which  means
     it will not work on filenames with spaces in them unless you
     have /bin/csh on your machine.) Of course, the shortest  way
     to do the above is:

          chmod 0644, <*.c>;

     Syntax

     A perl script consists of a  sequence  of  declarations  and
     commands.   The only things that need to be declared in perl
     are report formats and subroutines.  See the sections  below
     for  more information on those declarations.  All uninitial-
     ized user-created objects are assumed to start with  a  null
     or 0 value until they are defined by some explicit operation
     such as assignment.  The sequence of  commands  is  executed
     just once, unlike in sed and awk scripts, where the sequence
     of commands is executed for each  input  line.   While  this
     means  that  you must explicitly loop over the lines of your
     input file (or files), it also means you have much more con-
     trol  over  which files and which lines you look at.  (Actu-
     ally, I'm lying--it is possible to do an implicit loop  with
     either the -n or -p switch.)

     A declaration can be put anywhere a command can, but has  no
     effect   on   the  execution  of  the  primary  sequence  of
     commands--declarations all  take  effect  at  compile  time.
     Typically  all  the declarations are put at the beginning or
     the end of the script.

     Perl is, for the most part, a free-form language.  (The only
     exception to this is format declarations, for fairly obvious
     reasons.) Comments are indicated by  the  #  character,  and
     extend  to the end of the line.  If you attempt to use /* */
     C comments, it will be interpreted  either  as  division  or
     pattern  matching,  depending  on  the context.  So don't do
     that.

     Compound statements

     In perl, a sequence of commands may be treated as  one  com-
     mand by enclosing it in curly brackets.  We will call this a
     BLOCK.

     The following compound commands may be used to control flow:

          if (EXPR) BLOCK
          if (EXPR) BLOCK else BLOCK
          if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK
          LABEL while (EXPR) BLOCK
          LABEL while (EXPR) BLOCK continue BLOCK
          LABEL for (EXPR; EXPR; EXPR) BLOCK
          LABEL foreach VAR (ARRAY) BLOCK
          LABEL BLOCK continue BLOCK

     Note that, unlike C and Pascal, these are defined  in  terms
     of BLOCKs, not statements.  This means that the curly brack-
     ets are required--no dangling statements  allowed.   If  you
     want  to write conditionals without curly brackets there are
     several other ways to do it.  The following all do the  same
     thing:

          if (!open(foo)) { die "Can't open $foo: $!"; }
          die "Can't open $foo: $!" unless open(foo);
          open(foo) || die "Can't open $foo: $!"; # foo or bust!
          open(foo) ? 'hi mom' : die "Can't open $foo: $!";
                         # a bit exotic, that last one

     The if  statement  is  straightforward.   Since  BLOCKs  are
     always  bounded  by curly brackets, there is never any ambi-
     guity about which if an else goes with.  If you  use  unless
     in place of if, the sense of the test is reversed.

     The while statement  executes  the  block  as  long  as  the
     expression  is true (does not evaluate to the null string or
     0).  The LABEL is optional, and if present, consists  of  an
     identifier  followed  by  a colon.  The LABEL identifies the
     loop for the loop control statements next,  last,  and  redo
     (see  below).   If  there  is a continue BLOCK, it is always
     executed  just  before  the  conditional  is  about  to   be
     evaluated  again,  similarly to the third part of a for loop
     in C.  Thus it can be used to  increment  a  loop  variable,
     even when the loop has been continued via the next statement
     (similar to the C "continue" statement).

     If the word while is replaced by the word until,  the  sense
     of the test is reversed, but the conditional is still tested
     before the first iteration.

     In either the if or the while  statement,  you  may  replace
     "(EXPR)"  with  a  BLOCK, and the conditional is true if the
     value of the last command in that block is true.

     The for loop works  exactly  like  the  corresponding  while
     loop:

          for ($i = 1; $i < 10; $i++) {
               ...
          }

     is the same as

          $i = 1;
          while ($i < 10) {
               ...
          } continue {
               $i++;
          }

     The foreach loop iterates over a normal array value and sets
     the  variable  VAR  to be each element of the array in turn.
     The variable is implicitly local to the  loop,  and  regains
     its  former value upon exiting the loop.  The "foreach" key-
     word is actually identical to the "for" keyword, so you  can
     use  "foreach" for readability or "for" for brevity.  If VAR
     is omitted, $_ is set to each value.  If ARRAY is an  actual
     array  (as  opposed  to  an  expression  returning  an array
     value), you can modify each element of the array by  modify-
     ing VAR inside the loop.  Examples:

          for (@ary) { s/foo/bar/; }

          foreach $elem (@elements) {
               $elem *= 2;
          }

          for ((10,9,8,7,6,5,4,3,2,1,'BOOM')) {
               print $_, "\n"; sleep(1);
          }

          for (1..15) { print "Merry Christmas\n"; }

          foreach $item (split(/:[\\\n:]*/, $ENV{'TERMCAP'})) {
               print "Item: $item\n";
          }

     The BLOCK by itself (labeled or not) is equivalent to a loop
     that  executes  once.  Thus you can use any of the loop con-
     trol statements in it to leave or restart  the  block.   The
     continue  block is optional.  This construct is particularly
     nice for doing case structures.

          foo: {
               if (/^abc/) { $abc = 1; last foo; }
               if (/^def/) { $def = 1; last foo; }
               if (/^xyz/) { $xyz = 1; last foo; }
               $nothing = 1;
          }

     There is no official switch statement in perl, because there
     are  already several ways to write the equivalent.  In addi-
     tion to the above, you could write

          foo: {
               $abc = 1, last foo  if /^abc/;
               $def = 1, last foo  if /^def/;
               $xyz = 1, last foo  if /^xyz/;
               $nothing = 1;
          }

     or

          foo: {
               /^abc/ && do { $abc = 1; last foo; };
               /^def/ && do { $def = 1; last foo; };
               /^xyz/ && do { $xyz = 1; last foo; };
               $nothing = 1;
          }

     or

          foo: {
               /^abc/ && ($abc = 1, last foo);
               /^def/ && ($def = 1, last foo);
               /^xyz/ && ($xyz = 1, last foo);
               $nothing = 1;
          }

     or even

          if (/^abc/)
               { $abc = 1; }
          elsif (/^def/)
               { $def = 1; }
          elsif (/^xyz/)
               { $xyz = 1; }
          else
               {$nothing = 1;}

     As it happens, these  are  all  optimized  internally  to  a
     switch  structure,  so  perl  jumps  directly to the desired
     statement, and you needn't worry about perl executing a  lot
     of  unnecessary  statements  when  you  have  a string of 50
     elsifs, as long as you are testing the  same  simple  scalar
     variable  using  ==,  eq, or pattern matching as above.  (If
     you're curious as to whether the optimizer has done this for
     a  particular  case statement, you can use the -D1024 switch
     to list the syntax tree before execution.)

     Simple statements

     The only kind of simple statement is an expression evaluated
     for  its  side effects.  Every expression (simple statement)
     must be terminated with a semicolon.  Note that this is like
     C, but unlike Pascal (and awk).

     Any simple statement may optionally be followed by a  single
     modifier, just before the terminating semicolon.  The possi-
     ble modifiers are:

          if EXPR
          unless EXPR
          while EXPR
          until EXPR

     The if and unless modifiers  have  the  expected  semantics.
     The  while and until modifiers also have the expected seman-
     tics (conditional evaluated first), except when applied to a
     do-BLOCK or a do-SUBROUTINE command, in which case the block
     executes once before the conditional is evaluated.  This  is
     so that you can write loops like:

          do {
               $_ = <STDIN>;
               ...
          } until $_ eq ".\n";

     (See the do operator below.  Note also that the loop control
     commands  described  later  will NOT work in this construct,
     since modifiers don't take loop labels.  Sorry.)

     Expressions

     Since perl expressions work almost exactly  like  C  expres-
     sions, only the differences will be mentioned here.

     Here's what perl has that C doesn't:

     **      The exponentiation operator.

     **=     The exponentiation assignment operator.

     ()      The null list, used to initialize an array to null.

     .       Concatenation of two strings.

     .=      The concatenation assignment operator.

     eq      String equality (== is  numeric  equality).   For  a
             mnemonic  just  think  of "eq" as a string.  (If you
             are used to the awk behavior of using == for  either
             string or numeric equality based on the current form
             of the comparands, beware!   You  must  be  explicit
             here.)

     ne      String inequality (!= is numeric inequality).

     lt      String less than.

     gt      String greater than.

     le      String less than or equal.

     ge      String greater than or equal.

     cmp     String comparison, returning -1, 0, or 1.

     <=>     Numeric comparison, returning -1, 0, or 1.

     =~      Certain operations search or modify the string  "$_"
             by default.  This operator makes that kind of opera-
             tion work on some other string.  The right  argument
             is  a  search pattern, substitution, or translation.
             The  left  argument  is  what  is  supposed  to   be
             searched,  substituted, or translated instead of the
             default "$_".  The return value indicates  the  suc-
             cess of the operation.  (If the right argument is an
             expression other than a  search  pattern,  substitu-
             tion,  or translation, it is interpreted as a search
             pattern at run time.  This is less efficient than an
             explicit  search, since the pattern must be compiled
             every time the expression is  evaluated.)  The  pre-
             cedence  of  this operator is lower than unary minus
             and autoincrement/decrement, but higher than  every-
             thing else.

     !~      Just like =~ except the return value is negated.

     x       The repetition operator.  Returns a string  consist-
             ing of the left operand repeated the number of times
             specified by the right operand.  In  an  array  con-
             text,  if  the  left operand is a list in parens, it
             repeats the list.

                  print '-' x 80;          # print row of dashes
                  print '-' x80;      # illegal, x80 is identifier

                  print "\t" x ($tab/8), ' ' x ($tab%8);  # tab over

                  @ones = (1) x 80;        # an array of 80 1's
                  @ones = (5) x @ones;          # set all elements to 5

     x=      The repetition assignment operator.  Only  works  on
             scalars.

     ..      The range operator, which is  really  two  different
             operators  depending  on  the  context.  In an array
             context, returns an array  of  values  counting  (by
             ones)  from the left value to the right value.  This
             is useful for writing "for (1..10)"  loops  and  for
             doing slice operations on arrays.

             In a scalar context, ..  returns  a  boolean  value.
             The  operator  is bistable, like a flip-flop..  Each
             .. operator maintains its own boolean state.  It  is
             false  as  long  as its left operand is false.  Once
             the left operand is true, the range  operator  stays
             true  until  the  right operand is true, AFTER which
             the range operator becomes false again.  (It doesn't
             become  false  till the next time the range operator
             is evaluated.  It  can  become  false  on  the  same
             evaluation it became true, but it still returns true
             once.) The right operand is not evaluated while  the
             operator  is  in  the  "false"  state,  and the left
             operand is not evaluated while the  operator  is  in
             the  "true"  state.   The scalar .. operator is pri-
             marily intended for doing line number  ranges  after
             the fashion of sed or awk.  The precedence is a lit-
             tle lower than || and &&.   The  value  returned  is
             either  the  null  string  for  false, or a sequence
             number (beginning with 1) for  true.   The  sequence
             number  is  reset  for  each range encountered.  The
             final sequence number in a range has the string 'E0'
             appended  to  it,  which  doesn't affect its numeric
             value, but gives you something to search for if  you
             want  to  exclude the endpoint.  You can exclude the
             beginning point by waiting for the  sequence  number
             to  be  greater than 1.  If either operand of scalar
             .. is static, that operand is implicitly compared to
             the $. variable, the current line number.  Examples:

             As a scalar operator:
                 if (101 .. 200) { print; }     # print 2nd hundred lines

                 next line if (1 .. /^$/); # skip header lines

                 s/^/> / if (/^$/ .. eof());    # quote body

             As an array operator:
                 for (101 .. 200) { print; }    # print $_ 100 times

                 @foo = @foo[$[ .. $#foo]; # an expensive no-op
                 @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items

     -x      A file test.  This unary operator  takes  one  argu-
             ment,  either  a filename or a filehandle, and tests
             the associated file to  see  if  something  is  true
             about  it.   If  the  argument is omitted, tests $_,
             except for -t, which tests STDIN.  It returns 1  for
             true and '' for false, or the undefined value if the
             file doesn't exist.  Precedence is higher than logi-
             cal  and relational operators, but lower than arith-
             metic operators.  The operator may be any of:

                  -r   File is readable by effective uid.
                  -w   File is writable by effective uid.
                  -x   File is executable by effective uid.
                  -o   File is owned by effective uid.
                  -R   File is readable by real uid.
                  -W   File is writable by real uid.
                  -X   File is executable by real uid.
                  -O   File is owned by real uid.
                  -e   File exists.
                  -z   File has zero size.
                  -s   File has non-zero size (returns size).
                  -f   File is a plain file.
                  -d   File is a directory.
                  -l   File is a symbolic link.
                  -p   File is a named pipe (FIFO).
                  -S   File is a socket.
                  -b   File is a block special file.
                  -c   File is a character special file.
                  -u   File has setuid bit set.
                  -g   File has setgid bit set.
                  -k   File has sticky bit set.
                  -t   Filehandle is opened to a tty.
                  -T   File is a text file.
                  -B   File is a binary file (opposite of -T).
                  -M   Age of file in days when script started.
                  -A   Same for access time.
                  -C   Same for inode change time.

             The interpretation of the file permission  operators
             -r,  -R,  -w,  -W,  -x and -X is based solely on the
             mode of the file and the uids and gids of the  user.
             There  may be other reasons you can't actually read,
             write or execute the file.  Also note that, for  the
             superuser, -r, -R, -w and -W always return 1, and -x
             and -X return 1 if any execute bit  is  set  in  the
             mode.  Scripts run by the superuser may thus need to
             do a stat() in order to determine the actual mode of
             the  file,  or  temporarily set the uid to something
             else.

             Example:

                  while (<>) {
                       chop;
                       next unless -f $_;  # ignore specials
                       ...
                  }

             Note that -s/a/b/ does not do  a  negated  substitu-
             tion.   Saying  -exp($foo)  still works as expected,
             however--only single letters following a  minus  are
             interpreted as file tests.

             The -T and -B switches work as follows.   The  first
             block  or so of the file is examined for odd charac-
             ters such as strange control  codes  or  metacharac-
             ters.   If too many odd characters (>10%) are found,
             it's a -B file, otherwise it's a -T file.  Also, any
             file  containing  null  in  the  first block is con-
             sidered a binary file.  If -T or -B  is  used  on  a
             filehandle,  the  current  stdio  buffer is examined
             rather than the first block.  Both -T and -B  return
             TRUE on a null file, or a file at EOF when testing a
             filehandle.

     If any of the file tests (or either stat operator) are given
     the  special  filehandle consisting of a solitary underline,
     then the stat structure of the previous file test  (or  stat
     operator) is used, saving a system call.  (This doesn't work
     with -t, and you need to remember that  lstat  and  -l  will
     leave  values  in  the stat structure for the symbolic link,
     not the real file.) Example:

          print "Can do.\n" if -r $a || -w _ || -x _;

          stat($filename);
          print "Readable\n" if -r _;
          print "Writable\n" if -w _;
          print "Executable\n" if -x _;
          print "Setuid\n" if -u _;
          print "Setgid\n" if -g _;
          print "Sticky\n" if -k _;
          print "Text\n" if -T _;
          print "Binary\n" if -B _;

     Here is what C has that perl doesn't:

     unary &     Address-of operator.

     unary *     Dereference-address operator.

     (TYPE)      Type casting operator.

     Like C, perl does a certain amount of expression  evaluation
     at  compile  time,  whenever  it  determines that all of the
     arguments to  an  operator  are  static  and  have  no  side
     effects.   In  particular,  string  concatenation happens at
     compile time between literals that don't do variable substi-
     tution.   Backslash  interpretation  also happens at compile
     time.  You can say

          'Now is the time for all' . "\n" .
          'good men to come to.'

     and this all reduces to one string internally.

     The autoincrement operator has a little extra built-in magic
     to it.  If you increment a variable that is numeric, or that
     has ever been used in a numeric context, you  get  a  normal
     increment.   If, however, the variable has only been used in
     string contexts since it was set, and has a  value  that  is
     not  null  and  matches the pattern /^[a-zA-Z]*[0-9]*$/, the
     increment is done as a  string,  preserving  each  character
     within its range, with carry:

          print ++($foo = '99');   # prints '100'
          print ++($foo = 'a0');   # prints 'a1'
          print ++($foo = 'Az');   # prints 'Ba'
          print ++($foo = 'zz');   # prints 'aaa'

     The autodecrement is not magical.

     The range operator (in an array context) makes  use  of  the
     magical  autoincrement  algorithm if the minimum and maximum
     are strings.  You can say

          @alphabet = ('A' .. 'Z');

     to get all the letters of the alphabet, or

          $hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];

     to get a hexadecimal digit, or

          @z2 = ('01' .. '31');  print @z2[$mday];

     to get dates with leading zeros.  (If the final value speci-
     fied is not in the sequence that the magical increment would
     produce, the sequence goes until the  next  value  would  be
     longer than the final value specified.)

     The || and && operators differ from C's in that, rather than
     returning  0  or  1,  they  return the last value evaluated.
     Thus, a portable way to find out the  home  directory  might
     be:

          $home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
              (getpwuid($<))[7] || die "You're homeless!\n";

     Along with the literals and variables mentioned earlier, the
     operations in the following section can serve as terms in an
     expression.  Some of these operations  take  a  LIST  as  an
     argument.   Such  a  list  can consist of any combination of
     scalar arguments or array values; the array values  will  be
     included  in  the  list  as  if each individual element were
     interpolated at that point in the  list,  forming  a  longer
     single-dimensional array value.  Elements of the LIST should
     be separated by commas.  If an operation is listed both with
     and  without  parentheses around its arguments, it means you
     can either use it as a unary operator or as a function call.
     To  use  it  as  a function call, the next token on the same
     line must be a left parenthesis.  (There may be  intervening
     white  space.)  Such a function then has highest precedence,
     as you would expect from a function.   If  any  token  other
     than  a  left parenthesis follows, then it is a unary opera-
     tor, with a precedence depending only on  whether  it  is  a
     LIST  operator  or  not.   LIST  operators  have lowest pre-
     cedence.   All  other  unary  operators  have  a  precedence
     greater  than  relational operators but less than arithmetic
     operators.  See the section on Precedence.

     /PATTERN/
             See m/PATTERN/.

     ?PATTERN?
             This is just like the /pattern/ search, except  that
             it  matches  only  once  between  calls to the reset
             operator.  This is a useful  optimization  when  you
             only  want  to see the first occurrence of something
             in each file of a set of files, for instance.   Only
             ?? patterns local to the current package are reset.

     accept(NEWSOCKET,GENERICSOCKET)
             Does the same thing  that  the  accept  system  call
             does.   Returns  true  if it succeeded, false other-
             wise.  See example in section on  Interprocess  Com-
             munication.

     alarm(SECONDS)
     alarm SECONDS
             Arranges to have a SIGALRM delivered to this process
             after  the  specified  number  of  seconds (minus 1,
             actually) have elapsed.  Thus, alarm(15) will  cause
             a  SIGALRM at some point more than 14 seconds in the
             future.  Only one timer may  be  counting  at  once.
             Each  call disables the previous timer, and an argu-
             ment of 0 may be supplied  to  cancel  the  previous
             timer  without  starting  a  new  one.  The returned
             value is the amount of time remaining on the  previ-
             ous timer.

     atan2(Y,X)
             Returns the arctangent of Y/X in the  range  -PI  to
             PI.

     bind(SOCKET,NAME)
             Does the same thing that the bind system call  does.
             Returns true if it succeeded, false otherwise.  NAME
             should be a packed address of the  proper  type  for
             the  socket.  See example in section on Interprocess
             Communication.

     binmode(FILEHANDLE)
     binmode FILEHANDLE
             Arranges for the file to be read in "binary" mode in
             operating  systems  that  distinguish between binary
             and text files.  Files that are not read  in  binary
             mode  have CR LF sequences translated to LF on input
             and LF translated to CR LF on output.   Binmode  has
             no  effect  under Unix.  If FILEHANDLE is an expres-
             sion, the value is taken as the name of the filehan-
             dle.

     caller(EXPR)
     caller  Returns the context of the current subroutine call:

                  ($package,$filename,$line) = caller;

             With EXPR, returns some extra information  that  the
             debugger  uses to print a stack trace.  The value of
             EXPR indicates how  many  call  frames  to  go  back
             before the current one.

     chdir(EXPR)
     chdir EXPR
             Changes the working directory to EXPR, if  possible.
             If  EXPR  is  omitted,  changes  to  home directory.
             Returns 1 upon success, 0  otherwise.   See  example
             under die.

     chmod(LIST)
     chmod LIST
             Changes the permissions of a  list  of  files.   The
             first  element  of  the  list  must be the numerical
             mode.  Returns  the  number  of  files  successfully
             changed.

                  $cnt = chmod 0755, 'foo', 'bar';
                  chmod 0755, @executables;

     chop(LIST)
     chop(VARIABLE)
     chop VARIABLE
     chop    Chops off the last character of a string and returns
             the  character  chopped.   It's  used  primarily  to
             remove the newline from the end of an input  record,
             but  is  much  more efficient than s/\n// because it
             neither scans nor copies the string.  If VARIABLE is
             omitted, chops $_.  Example:

                  while (<>) {
                       chop;     # avoid \n on last field
                       @array = split(/:/);
                       ...
                  }

             You can actually chop  anything  that's  an  lvalue,
             including an assignment:

                  chop($cwd = `pwd`);
                  chop($answer = <STDIN>);

             If you chop a list, each element is  chopped.   Only
             the value of the last chop is returned.

     chown(LIST)
     chown LIST
             Changes the owner (and group) of a  list  of  files.
             The  first  two  elements  of  the  list must be the
             NUMERICAL uid and gid, in that order.   Returns  the
             number of files successfully changed.

                  $cnt = chown $uid, $gid, 'foo', 'bar';
                  chown $uid, $gid, @filenames;

             Here's an example that looks up non-numeric uids  in
             the passwd file:

                  print "User: ";
                  $user = <STDIN>;
                  chop($user);
                  print "Files: "
                  $pattern = <STDIN>;
                  chop($pattern);
                  open(pass, '/etc/passwd')
                       || die "Can't open passwd: $!\n";
                  while (<pass>) {
                       ($login,$pass,$uid,$gid) = split(/:/);
                       $uid{$login} = $uid;
                       $gid{$login} = $gid;
                  }
                  @ary = <${pattern}>;     # get filenames
                  if ($uid{$user} eq '') {
                       die "$user not in passwd file";
                  }
                  else {
                       chown $uid{$user}, $gid{$user}, @ary;
                  }

     chroot(FILENAME)
     chroot FILENAME
             Does the same as the system call of that  name.   If
             you  don't  know what it does, don't worry about it.
             If FILENAME is omitted, does chroot to $_.

     close(FILEHANDLE)
     close FILEHANDLE
             Closes the file or pipe  associated  with  the  file
             handle.   You  don't have to close FILEHANDLE if you
             are immediately going to  do  another  open  on  it,
             since  open will close it for you.  (See open.) How-
             ever, an explicit close on an input file resets  the
             line  counter ($.), while the implicit close done by
             open does not.  Also, closing a pipe will  wait  for
             the  process  executing  on the pipe to complete, in
             case you want to look at  the  output  of  the  pipe
             afterwards.  Closing a pipe explicitly also puts the
             status value of the command into $?.  Example:

                  open(OUTPUT, '|sort >foo');   # pipe to sort
                  ...  # print stuff to output
                  close OUTPUT;       # wait for sort to finish
                  open(INPUT, 'foo'); # get sort's results

             FILEHANDLE may be an expression  whose  value  gives
             the real filehandle name.

     closedir(DIRHANDLE)
     closedir DIRHANDLE
             Closes a directory opened by opendir().

     connect(SOCKET,NAME)
             Does the same thing that  the  connect  system  call
             does.   Returns  true  if it succeeded, false other-
             wise.  NAME should  be  a  package  address  of  the
             proper  type for the socket.  See example in section
             on Interprocess Communication.

     cos(EXPR)
     cos EXPR
             Returns the cosine of EXPR (expressed  in  radians).
             If EXPR is omitted takes cosine of $_.

     crypt(PLAINTEXT,SALT)
             Encrypts a string exactly like the crypt()  function
             in  the C library.  Useful for checking the password
             file for lousy passwords.   Only  the  guys  wearing
             white hats should do this.

     dbmclose(ASSOC_ARRAY)
     dbmclose ASSOC_ARRAY
             Breaks the binding between a dbm file and an associ-
             ative  array.   The values remaining in the associa-
             tive array are meaningless unless you happen to want
             to  know  what  was  in  the cache for the dbm file.
             This function is only useful if you have ndbm.

     dbmopen(ASSOC,DBNAME,MODE)
             This binds a dbm or  ndbm  file  to  an  associative
             array.   ASSOC is the name of the associative array.
             (Unlike normal open, the first  argument  is  NOT  a
             filehandle,  even though it looks like one).  DBNAME
             is the name of the database  (without  the  .dir  or
             .pag extension).  If the database does not exist, it
             is created with protection  specified  by  MODE  (as
             modified  by  the  umask).  If your system only sup-
             ports the older dbm functions, you may perform  only
             one  dbmopen  in  your  program.  If your system has
             neither dbm nor ndbm,  calling  dbmopen  produces  a
             fatal error.

             Values assigned to the associative  array  prior  to
             the  dbmopen  are  lost.  A certain number of values
             from the dbm file are cached in memory.  By  default
             this number is 64, but you can increase it by preal-
             locating that number of garbage entries in the asso-
             ciative array before the dbmopen.  You can flush the
             cache if necessary with the reset command.

             If you don't have write access to the dbm file,  you
             can  only  read associative array variables, not set
             them.  If you want to test whether  you  can  write,
             either  use  file tests or try setting a dummy array
             entry inside an eval, which will trap the error.

             Note that functions such as keys() and values()  may
             return  huge  array  values  when  used on large dbm
             files.  You may prefer to use the each() function to
             iterate over large dbm files.  Example:

                  # print out history file offsets
                  dbmopen(HIST,'/usr/lib/news/history',0666);
                  while (($key,$val) = each %HIST) {
                       print $key, ' = ', unpack('L',$val), "\n";
                  }
                  dbmclose(HIST);

     defined(EXPR)
     defined EXPR
             Returns a boolean value saying  whether  the  lvalue
             EXPR  has  a  real  value  or  not.  Many operations
             return the undefined value under exceptional  condi-
             tions,  such as end of file, uninitialized variable,
             system error and such.  This function allows you  to
             distinguish  between  an undefined null string and a
             defined  null  string  with  operations  that  might
             return a real null string, in particular referencing
             elements of an array.  You may also check to see  if
             arrays  or  subroutines  exist.   Use  on predefined
             variables is not  guaranteed  to  produce  intuitive
             results.  Examples:

                  print if defined $switch{'D'};
                  print "$val\n" while defined($val = pop(@ary));
                  die "Can't readlink $sym: $!"
                       unless defined($value = readlink $sym);
                  eval '@foo = ()' if defined(@foo);
                  die "No XYZ package defined" unless defined %_XYZ;
                  sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }

             See also undef.

     delete $ASSOC{KEY}
             Deletes the specified value from the specified asso-
             ciative  array.   Returns  the deleted value, or the
             undefined value if nothing  was  deleted.   Deleting
             from $ENV{} modifies the environment.  Deleting from
             an array bound to a dbm file deletes the entry  from
             the dbm file.

             The following deletes all the values of an  associa-
             tive array:

                  foreach $key (keys %ARRAY) {
                       delete $ARRAY{$key};
                  }

             (But it would be faster to use  the  reset  command.
             Saying undef %ARRAY is faster yet.)

     die(LIST)
     die LIST
             Outside of an eval, prints  the  value  of  LIST  to
             STDERR  and  exits  with  the  current  value  of $!
             (errno).  If $! is 0, exits with the value of ($? >>
             8)  (`command`  status).   If  ($? >> 8) is 0, exits
             with 255.  Inside an  eval,  the  error  message  is
             stuffed  into $@ and the eval is terminated with the
             undefined value.

             Equivalent examples:

                  die "Can't cd to spool: $!\n"
                       unless chdir '/usr/spool/news';

                  chdir '/usr/spool/news' || die "Can't cd to spool: $!\n"

             If the value of EXPR does not end in a newline,  the
             current script line number and input line number (if
             any) are also printed, and a  newline  is  supplied.
             Hint:  sometimes  appending ", stopped" to your mes-
             sage will cause it to make  better  sense  when  the
             string  "at  foo line 123" is appended.  Suppose you
             are running script "canasta".

                  die "/etc/games is no good";
                  die "/etc/games is no good, stopped";

             produce, respectively

                  /etc/games is no good at canasta line 123.
                  /etc/games is no good, stopped at canasta line 123.

             See also exit.

     do BLOCK
             Returns  the  value  of  the  last  command  in  the
             sequence of commands indicated by BLOCK.  When modi-
             fied by a loop modifier,  executes  the  BLOCK  once
             before testing the loop condition.  (On other state-
             ments  the  loop  modifiers  test  the   conditional
             first.)

     do SUBROUTINE (LIST)
             Executes a SUBROUTINE declared by a sub declaration,
             and   returns  the  value  of  the  last  expression
             evaluated in SUBROUTINE.  If there is no  subroutine
             by  that name, produces a fatal error.  (You may use
             the "defined" operator to determine if a  subroutine
             exists.)  If you pass arrays as part of LIST you may
             wish to pass the length of the  array  in  front  of
             each  array.   (See the section on Subroutines later
             on.) The parentheses are required to avoid confusion
             with the "do EXPR" form.

             SUBROUTINE may also be a single scalar variable,  in
             which  case the name of the subroutine to execute is
             taken from the variable.

             As an alternate (and preferred) form, you may call a
             subroutine  by prefixing the name with an ampersand:
             &foo(@args).  If you aren't passing  any  arguments,
             you  don't have to use parentheses.  If you omit the
             parentheses, no @_ array is passed  to  the  subrou-
             tine.   The  &  form is also used to specify subrou-
             tines to the defined and undef operators:

                  if (defined &$var) { &$var($parm); undef &$var; }

     do EXPR Uses the value of EXPR as a  filename  and  executes
             the contents of the file as a perl script.  Its pri-
             mary use is to include subroutines from a perl  sub-
             routine library.

                  do 'stat.pl';

             is just like

                  eval `cat stat.pl`;

             except that it's more efficient, more concise, keeps
             track  of  the  current filename for error messages,
             and searches all the -I libraries if the file  isn't
             in the current directory (see also the @INC array in
             Predefined Names).  It's the same, however, in  that
             it  does reparse the file every time you call it, so
             if you are going to use the file inside a  loop  you
             might  prefer to use -P and #include, at the expense
             of a little more startup time.   (The  main  problem
             with #include is that cpp doesn't grok # comments--a
             workaround is to use ";#" for standalone  comments.)
             Note that the following are NOT equivalent:

                  do $foo;  # eval a file
                  do $foo();     # call a subroutine

             Note that inclusion of library  routines  is  better
             done with the "require" operator.

     dump LABEL
             This causes an immediate core dump.  Primarily  this
             is  so  that  you can use the undump program to turn
             your core dump into an executable binary after  hav-
             ing  initialized all your variables at the beginning
             of the program.  When the new binary is executed  it
             will begin by executing a "goto LABEL" (with all the
             restrictions that goto suffers).  Think of it  as  a
             goto  with  an  intervening core dump and reincarna-
             tion.  If LABEL is  omitted,  restarts  the  program
             from the top.  WARNING: any files opened at the time
             of the dump will NOT be open any more when the  pro-
             gram is reincarnated, with possible resulting confu-
             sion on the part of perl.  See also -u.

             Example:

                  #!/usr/bin/perl
                  require 'getopt.pl';
                  require 'stat.pl';
                  %days = (
                      'Sun',1,
                      'Mon',2,
                      'Tue',3,
                      'Wed',4,
                      'Thu',5,
                      'Fri',6,
                      'Sat',7);

                  dump QUICKSTART if $ARGV[0] eq '-d';

                 QUICKSTART:
                  do Getopt('f');

     each(ASSOC_ARRAY)
     each ASSOC_ARRAY
             Returns a 2 element array consisting of the key  and
             value for the next value of an associative array, so
             that you can iterate over it.  Entries are  returned
             in  an  apparently  random order.  When the array is
             entirely read, a null array is returned (which  when
             assigned produces a FALSE (0) value).  The next call
             to each() after that  will  start  iterating  again.
             The  iterator  can  be reset only by reading all the
             elements from the array.  You must  not  modify  the
             array  while  iterating  over it.  There is a single
             iterator for each associative array, shared  by  all
             each(),  keys()  and  values() function calls in the
             program.  The following prints out your  environment
             like  the  printenv  program,  only  in  a different
             order:

                  while (($key,$value) = each %ENV) {
                       print "$key=$value\n";
                  }

             See also keys() and values().

     eof(FILEHANDLE)
     eof()
     eof     Returns 1 if the next read on FILEHANDLE will return
             end of file, or if FILEHANDLE is not open.  FILEHAN-
             DLE may be an expression whose value gives the  real
             filehandle  name.  (Note that this function actually
             reads a character and then ungetc's it, so it is not
             very  useful  in  an  interactive  context.)  An eof
             without an argument returns the eof status  for  the
             last file read.  Empty parentheses () may be used to
             indicate the pseudo file formed of the files  listed
             on the command line, i.e. eof() is reasonable to use
             inside a while (<>) loop to detect the end  of  only
             the  last  file.   Use  eof(ARGV) or eof without the
             parentheses to test EACH file in a while (<>)  loop.
             Examples:

                  # insert dashes just before last line of last file
                  while (<>) {
                       if (eof()) {
                            print "--------------\n";
                       }
                       print;
                  }

                  # reset line numbering on each input file
                  while (<>) {
                       print "$.\t$_";
                       if (eof) {     # Not eof().
                            close(ARGV);
                       }
                  }

     eval(EXPR)
     eval EXPR
     eval BLOCK
             EXPR is parsed and executed as if it were  a  little
             perl  program.  It is executed in the context of the
             current perl program, so that any variable settings,
             subroutine  or format definitions remain afterwards.
             The value returned is the value of the last  expres-
             sion  evaluated, just as with subroutines.  If there
             is a syntax error or runtime error, or a die  state-
             ment  is executed, an undefined value is returned by
             eval, and $@ is set to the error message.  If  there
             was  no error, $@ is guaranteed to be a null string.
             If EXPR is omitted, evaluates $_.  The  final  semi-
             colon, if any, may be omitted from the expression.

             Note that, since eval traps otherwise-fatal  errors,
             it  is  useful  for determining whether a particular
             feature (such as dbmopen or symlink) is implemented.
             It  is  also  Perl's  exception  trapping mechanism,
             where the die operator is used to raise exceptions.

             If the code to be executed doesn't vary, you may use
             the  eval-BLOCK form to trap run-time errors without
             incurring the penalty of recompiling each time.  The
             error,  if any, is still returned in $@.  Evaluating
             a  single-quoted  string  (as  EXPR)  has  the  same
             effect,  except that the eval-EXPR form reports syn-
             tax errors at run time via  $@,  whereas  the  eval-
             BLOCK  form  reports  syntax errors at compile time.
             The eval-EXPR form is optimized  to  eval-BLOCK  the
             first time it succeeds.  (Since the replacement side
             of a  substitution  is  considered  a  single-quoted
             string when you use the e modifier, the same optimi-
             zation occurs there.)  Examples:

                  # make divide-by-zero non-fatal
                  eval { $answer = $a / $b; }; warn $@ if $@;

                  # optimized to same thing after first use
                  eval '$answer = $a / $b'; warn $@ if $@;

                  # a compile-time error
                  eval { $answer = };

                  # a run-time error
                  eval '$answer =';   # sets $@

     exec(LIST)
     exec LIST
             If there is more than one argument in  LIST,  or  if
             LIST  is  an  array  with more than one value, calls
             execvp() with the arguments in LIST.   If  there  is
             only  one  scalar  argument, the argument is checked
             for shell metacharacters.  If  there  are  any,  the
             entire  argument is passed to "/bin/sh -c" for pars-
             ing.  If there are none, the argument is split  into
             words and passed directly to execvp(), which is more
             efficient.  Note: exec (and  system)  do  not  flush
             your  output  buffer,  so  you may need to set $| to
             avoid lost output.  Examples:

                  exec '/bin/echo', 'Your arguments are: ', @ARGV;
                  exec "sort $outfile | uniq";

             If you don't really want to execute the first  argu-
             ment, but want to lie to the program you are execut-
             ing about its own name, you can specify the  program
             you  actually  want  to  run  by assigning that to a
             variable and putting the name  of  the  variable  in
             front  of  the  LIST  without a comma.  (This always
             forces interpretation of the LIST as a  multi-valued
             list,  even  if there is only a single scalar in the
             list.) Example:

                  $shell = '/bin/csh';
                  exec $shell '-sh';       # pretend it's a login shell

     exit EXPR
             Evaluates  EXPR  and  exits  immediately  with  that
             value.  Example:

                  $ans = <STDIN>;
                  exit 0 if $ans =~ /^[Xx]/;

             See also die.  If EXPR  is  omitted,  exits  with  0
             status.

     exp(EXPR)
     exp EXPR
             Returns e to the power of EXPR.  If EXPR is omitted,
             gives exp($_).

     fcntl(FILEHANDLE,FUNCTION,SCALAR)
             Implements the fcntl(2) function.   You'll  probably
             have to say

                  require "fcntl.ph"; # probably /usr/local/lib/perl/fcntl.ph

             first to get the correct function  definitions.   If
             fcntl.ph  doesn't  exist or doesn't have the correct
             definitions you'll have to roll your own,  based  on
             your  C  header files such as <sys/fcntl.h>.  (There
             is a perl script called h2ph  that  comes  with  the
             perl  kit which may help you in this.) Argument pro-
             cessing and  value  return  works  just  like  ioctl
             below.   Note  that fcntl will produce a fatal error
             if  used  on  a  machine  that   doesn't   implement
             fcntl(2).

     fileno(FILEHANDLE)
     fileno FILEHANDLE
             Returns the file descriptor for a filehandle.   Use-
             ful  for  constructing  bitmaps  for  select().   If
             FILEHANDLE is an expression, the value is  taken  as
             the name of the filehandle.

     flock(FILEHANDLE,OPERATION)
             Calls flock(2) on FILEHANDLE.  See manual  page  for
             flock(2)  for definition of OPERATION.  Returns true
             for success, false on failure.  Will produce a fatal
             error  if  used  on a machine that doesn't implement
             flock(2).  Here's a mailbox appender  for  BSD  sys-
             tems.

                  $LOCK_SH = 1;
                  $LOCK_EX = 2;
                  $LOCK_NB = 4;
                  $LOCK_UN = 8;

                  sub lock {
                      flock(MBOX,$LOCK_EX);
                      # and, in case someone appended
                      # while we were waiting...
                      seek(MBOX, 0, 2);
                  }

                  sub unlock {
                      flock(MBOX,$LOCK_UN);
                  }

                  open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
                       || die "Can't open mailbox: $!";

                  do lock();
                  print MBOX $msg,"\n\n";
                  do unlock();

     fork    Does a fork() call.  Returns the child  pid  to  the
             parent  process  and  0 to the child process.  Note:
             unflushed   buffers   remain   unflushed   in   both
             processes,  which  means  you  may need to set $| to
             avoid duplicate output.

     getc(FILEHANDLE)
     getc FILEHANDLE
     getc    Returns the  next  character  from  the  input  file
             attached to FILEHANDLE, or a null string at EOF.  If
             FILEHANDLE is omitted, reads from STDIN.

     getlogin
             Returns the current login from  /etc/utmp,  if  any.
             If null, use getpwuid.

                  $login  =  getlogin  ||  (getpwuid($<))[0]   ||
             "Somebody";

     getpeername(SOCKET)
             Returns the packed sockaddr address of other end  of
             the SOCKET connection.

                  # An internet sockaddr
                  $sockaddr = 'S n a4 x8';
                  $hersockaddr = getpeername(S);
                  ($family, $port, $heraddr) =
                            unpack($sockaddr,$hersockaddr);

     getpgrp(PID)
     getpgrp PID
             Returns the current process group for the  specified
             PID,  0  for  the  current  process.  Will produce a
             fatal error if used on a machine that doesn't imple-
             ment  getpgrp(2).   If EXPR is omitted, returns pro-
             cess group of current process.

     getppid Returns the process id of the parent process.

     getpriority(WHICH,WHO)
             Returns the current priority for a process,  a  pro-
             cess  group,  or a user.  (See getpriority(2).) Will
             produce a fatal error if  used  on  a  machine  that
             doesn't implement getpriority(2).

     getgrnam(NAME)
     gethostbyname(NAME)
     getnetbyname(NAME)
     getprotobyname(NAME)
     getpwuid(UID)
     getgrgid(GID)
     getservbyname(NAME,PROTO)
     gethostbyaddr(ADDR,ADDRTYPE)
     getnetbyaddr(ADDR,ADDRTYPE)
     getprotobynumber(NUMBER)
     getservbyport(PORT,PROTO)
     getpwent
     getgrent
     gethostent
     getnetent
     getprotoent
     getservent
     setpwent
     setgrent
     sethostent(STAYOPEN)
     setnetent(STAYOPEN)
     setprotoent(STAYOPEN)
     setservent(STAYOPEN)
     endpwent
     endgrent
     endhostent
     endnetent
     endprotoent
     endservent
             These routines perform the same functions  as  their
             counterparts  in  the  system  library.   The return
             values from the various get routines are as follows:

                  ($name,$passwd,$uid,$gid,
                     $quota,$comment,$gcos,$dir,$shell) = getpw...
                  ($name,$passwd,$gid,$members) = getgr...
                  ($name,$aliases,$addrtype,$length,@addrs) = gethost...
                  ($name,$aliases,$addrtype,$net) = getnet...
                  ($name,$aliases,$proto) = getproto...
                  ($name,$aliases,$port,$proto) = getserv...

             The $members value returned by getgr... is  a  space
             separated  list of the login names of the members of
             the group.

             The @addrs value returned by  the  gethost...  func-
             tions is a list of the raw addresses returned by the
             corresponding system library call.  In the  Internet
             domain,  each address is four bytes long and you can
             unpack it by saying something like:

                  ($a,$b,$c,$d) = unpack('C4',$addr[0]);

     getsockname(SOCKET)
             Returns the packed sockaddr address of this  end  of
             the SOCKET connection.

                  # An internet sockaddr
                  $sockaddr = 'S n a4 x8';
                  $mysockaddr = getsockname(S);
                  ($family, $port, $myaddr) =
                            unpack($sockaddr,$mysockaddr);

     getsockopt(SOCKET,LEVEL,OPTNAME)
             Returns the socket option requested, or undefined if
             there is an error.

     gmtime(EXPR)
     gmtime EXPR
             Converts a time as returned by the time function  to
             a  9-element  array  with  the time analyzed for the
             Greenwich timezone.  Typically used as follows:

             ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                           gmtime(time);

             All array elements are numeric,  and  come  straight
             out  of  a struct tm.  In particular this means that
             $mon has the range 0..11 and  $wday  has  the  range
             0..6.  If EXPR is omitted, does gmtime(time).

     goto LABEL
             Finds the statement labeled with LABEL  and  resumes
             execution  there.   Currently  you  may  only  go to
             statements in the main body of the program that  are
             not nested inside a do {} construct.  This statement
             is not implemented very  efficiently,  and  is  here
             only  to  make the sed-to-perl translator easier.  I
             may change its semantics  at  any  time,  consistent
             with  support for translated sed scripts.  Use it at
             your own risk.  Better yet, don't use it at all.

     grep(EXPR,LIST)
             Evaluates EXPR for each  element  of  LIST  (locally
             setting  $_  to  each element) and returns the array
             value consisting of those  elements  for  which  the
             expression  evaluated to true.  In a scalar context,
             returns the number of times the expression was true.

                  @foo = grep(!/^#/, @bar);    # weed out comments

             Note that, since $_ is a reference  into  the  array
             value,  it can be used to modify the elements of the
             array.  While this is useful and supported,  it  can
             cause  bizarre  results  if  the LIST is not a named
             array.

     hex(EXPR)
     hex EXPR
             Returns the decimal value of EXPR interpreted as  an
             hex  string.  (To interpret strings that might start
             with 0 or 0x see oct().) If EXPR  is  omitted,  uses
             $_.

     index(STR,SUBSTR,POSITION)
     index(STR,SUBSTR)
             Returns the position  of  the  first  occurrence  of
             SUBSTR  in STR at or after POSITION.  If POSITION is
             omitted, starts searching from the beginning of  the
             string.  The return value is based at 0, or whatever
             you've set the $[ variable to.  If the substring  is
             not  found,  returns  one  less than the base, ordi-
             narily -1.

     int(EXPR)
     int EXPR
             Returns the integer portion of  EXPR.   If  EXPR  is
             omitted, uses $_.

     ioctl(FILEHANDLE,FUNCTION,SCALAR)
             Implements the ioctl(2) function.   You'll  probably
             have to say

                  require "ioctl.ph"; # probably /usr/local/lib/perl/ioctl.ph

             first to get the correct function  definitions.   If
             ioctl.ph  doesn't  exist or doesn't have the correct
             definitions you'll have to roll your own,  based  on
             your  C  header files such as <sys/ioctl.h>.  (There
             is a perl script called h2ph  that  comes  with  the
             perl kit which may help you in this.) SCALAR will be
             read and/or written  depending  on  the  FUNCTION--a
             pointer to the string value of SCALAR will be passed
             as the third argument of the actual ioctl call.  (If
             SCALAR  has  no string value but does have a numeric
             value, that value  will  be  passed  rather  than  a
             pointer  to  the string value.  To guarantee this to
             be true, add a 0 to the scalar before using it.) The
             pack() and unpack() functions are useful for manipu-
             lating the values of  structures  used  by  ioctl().

             The  following  example  sets the erase character to
             DEL.

                  require 'ioctl.ph';
                  $sgttyb_t = "ccccs";          # 4 chars and a short
                  if (ioctl(STDIN,$TIOCGETP,$sgttyb)) {
                       @ary = unpack($sgttyb_t,$sgttyb);
                       $ary[2] = 127;
                       $sgttyb = pack($sgttyb_t,@ary);
                       ioctl(STDIN,$TIOCSETP,$sgttyb)
                            || die "Can't ioctl: $!";
                  }

             The return value of ioctl (and fcntl) is as follows:

                  if OS returns:           perl returns:
                    -1                       undefined value
                    0                        string "0 but true"
                    anything else            that number

             Thus perl returns  true  on  success  and  false  on
             failure,  yet  you  can  still  easily determine the
             actual value returned by the operating system:

                  ($retval = ioctl(...)) || ($retval = -1);
                  printf "System returned %d\n", $retval;

     join(EXPR,LIST)
     join(EXPR,ARRAY)
             Joins the separate strings of LIST or ARRAY  into  a
             single  string with fields separated by the value of
             EXPR, and returns the string.  Example:

             $_ = join(':',
                       $login,$passwd,$uid,$gid,$gcos,$home,$shell);

             See split.

     keys(ASSOC_ARRAY)
     keys ASSOC_ARRAY
             Returns a normal array consisting of all the keys of
             the  named associative array.  The keys are returned
             in an apparently random order, but it  is  the  same
             order as either the values() or each() function pro-
             duces (given that the associative array has not been
             modified).   Here  is  yet another way to print your
             environment:

                  @keys = keys %ENV;
                  @values = values %ENV;
                  while ($#keys >= 0) {
                       print pop(@keys), '=', pop(@values), "\n";
                  }

             or how about sorted by key:

                  foreach $key (sort(keys %ENV)) {
                       print $key, '=', $ENV{$key}, "\n";
                  }

     kill(LIST)
     kill LIST
             Sends a signal to a list of  processes.   The  first
             element  of  the  list  must  be the signal to send.
             Returns the number of  processes  successfully  sig-
             naled.

                  $cnt = kill 1, $child1, $child2;
                  kill 9, @goners;

             If the signal  is  negative,  kills  process  groups
             instead of processes.  (On System V, a negative pro-
             cess number  will  also  kill  process  groups,  but
             that's  not  portable.) You may use a signal name in
             quotes.

     last LABEL
     last    The last command is like the break  statement  in  C
             (as used in loops); it immediately exits the loop in
             question.  If the  LABEL  is  omitted,  the  command
             refers  to  the  innermost enclosing loop.  The con-
             tinue block, if any, is not executed:

                  line: while (<STDIN>) {
                       last line if /^$/;  # exit when done with header
                       ...
                  }

     length(EXPR)
     length EXPR
             Returns the length in characters  of  the  value  of
             EXPR.  If EXPR is omitted, returns length of $_.

     link(OLDFILE,NEWFILE)
             Creates a new filename linked to the  old  filename.

             Returns 1 for success, 0 otherwise.

     listen(SOCKET,QUEUESIZE)
             Does the same thing  that  the  listen  system  call
             does.   Returns  true  if it succeeded, false other-
             wise.  See example in section on  Interprocess  Com-
             munication.

     local(LIST)
             Declares the listed variables to  be  local  to  the
             enclosing  block, subroutine, eval or "do".  All the
             listed elements must be legal lvalues.  This  opera-
             tor  works  by  saving  the  current values of those
             variables in LIST on a hidden  stack  and  restoring
             them  upon  exiting  the  block, subroutine or eval.
             This means that called subroutines can  also  refer-
             ence  the  local  variable,  but not the global one.
             The LIST may be assigned to if desired, which allows
             you to initialize your local variables.  (If no ini-
             tializer is given for a particular variable,  it  is
             created  with  an undefined value.) Commonly this is
             used to name the parameters to a subroutine.   Exam-
             ples:

                  sub RANGEVAL {
                       local($min, $max, $thunk) = @_;
                       local($result) = '';
                       local($i);

                       # Presumably $thunk makes reference to $i

                       for ($i = $min; $i < $max; $i++) {
                            $result .= eval $thunk;
                       }

                       $result;
                  }

                  if ($sw eq '-v') {
                      # init local array with global array
                      local(@ARGV) = @ARGV;
                      unshift(@ARGV,'echo');
                      system @ARGV;
                  }
                  # @ARGV restored

                  # temporarily add to digits associative array
                  if ($base12) {
                       # (NOTE: not claiming this is efficient!)
                       local(%digits) = (%digits,'t',10,'e',11);
                       do parse_num();
                  }

             Note that local() is a run-time command, and so gets
             executed  every  time  through a loop, using up more
             stack storage each time until it's all  released  at
             once when the loop is exited.

     localtime(EXPR)
     localtime EXPR
             Converts a time as returned by the time function  to
             a  9-element  array  with  the time analyzed for the
             local timezone.  Typically used as follows:

             ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                           localtime(time);

             All array elements are numeric,  and  come  straight
             out  of  a struct tm.  In particular this means that
             $mon has the range 0..11 and  $wday  has  the  range
             0..6.  If EXPR is omitted, does localtime(time).

     log(EXPR)
     log EXPR
             Returns logarithm (base e)  of  EXPR.   If  EXPR  is
             omitted, returns log of $_.

     lstat(FILEHANDLE)
     lstat FILEHANDLE
     lstat(EXPR)
     lstat SCALARVARIABLE
             Does the same thing  as  the  stat()  function,  but
             stats  a  symbolic link instead of the file the sym-
             bolic link points to.  If symbolic links  are  unim-
             plemented on your system, a normal stat is done.

     m/PATTERN/gio
     /PATTERN/gio
             Searches a string for a pattern match,  and  returns
             true  (1)  or false ('').  If no string is specified
             via  the  =~  or  !~  operator,  the  $_  string  is
             searched.  (The string specified with =~ need not be
             an lvalue--it may be the  result  of  an  expression
             evaluation,   but   remember  the  =~  binds  rather
             tightly.) See also the section  on  Regular  Expres-
             sions.

             If / is  the  delimiter  then  the  initial  'm'  is
             optional.   With  the  'm'  you  can use any pair of
             non-alphanumeric characters as delimiters.  This  is
             particularly  useful  for  matching  Unix path names
             that contain '/'.  If the final  delimiter  is  fol-
             lowed  by  the  optional letter 'i', the matching is
             done in a case-insensitive manner.  PATTERN may con-
             tain  references  to scalar variables, which will be
             interpolated (and the pattern recompiled) every time
             the  pattern search is evaluated.  (Note that $) and
             $| may not be interpolated because  they  look  like
             end-of-string  tests.) If you want such a pattern to
             be compiled only once, add an "o" after the trailing
             delimiter.   This avoids expensive run-time recompi-
             lations, and is useful when the value you are inter-
             polating  won't  change over the life of the script.
             If the PATTERN evaluates to a null string, the  most
             recent   successful   regular   expression  is  used
             instead.

             If used in a context that requires an array value, a
             pattern  match  returns  an  array consisting of the
             subexpressions matched by  the  parentheses  in  the
             pattern, i.e. ($1, $2, $3...).  It does NOT actually
             set $1, $2, etc. in this case, nor does it  set  $+,
             $`,  $&  or $'.  If the match fails, a null array is
             returned.  If the match succeeds, but there were  no
             parentheses, an array value of (1) is returned.

             Examples:

                 open(tty, '/dev/tty');
                 <tty> =~ /^y/i && do foo();    # do foo if desired

                 if (/Version: *([0-9.]*)/) { $version = $1; }

                 next if m#^/usr/spool/uucp#;

                 # poor man's grep
                 $arg = shift;
                 while (<>) {
                      print if /$arg/o;    # compile only once
                 }

                 if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))

             This last example splits $foo  into  the  first  two
             words  and  the  remainder  of the line, and assigns
             those three fields to $F1, $F2 and $Etc.  The condi-
             tional  is true if any variables were assigned, i.e.
             if the pattern matched.

             The   "g"   modifier   specifies   global    pattern
             matching--that   is,   matching  as  many  times  as
             possible within the string.  How it behaves  depends
             on  the  context.  In an array context, it returns a
             list of  all  the  substrings  matched  by  all  the
             parentheses in the regular expression.  If there are
             no parentheses, it returns a list of all the matched
             strings,  as  if  there  were parentheses around the
             whole pattern.  In a  scalar  context,  it  iterates
             through  the  string,  returning  TRUE  each time it
             matches, and FALSE when it eventually  runs  out  of
             matches.   (In  other  words,  it remembers where it
             left off last time and restarts the search  at  that
             point.)   It presumes that you have not modified the
             string since the last match.  Modifying  the  string
             between  matches  may  result in undefined behavior.
             (You can actually get away with  in-place  modifica-
             tions  via substr() that do not change the length of
             the entire string.  In general, however, you  should
             be using s///g for such modifications.)  Examples:

                  # array context
                  ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g);

                  # scalar context
                  $/ = 1; $* = 1;
                  while ($paragraph = <>) {
                      while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) {
                       $sentences++;
                      }
                  }
                  print "$sentences\n";

     mkdir(FILENAME,MODE)
             Creates the directory specified  by  FILENAME,  with
             permissions   specified  by  MODE  (as  modified  by
             umask).  If it succeeds it returns 1,  otherwise  it
             returns 0 and sets $! (errno).

     msgctl(ID,CMD,ARG)
             Calls the System V IPC function msgctl.  If  CMD  is
             &IPC_STAT,  then  ARG  must be a variable which will
             hold the returned msqid_ds structure.  Returns  like
             ioctl:  the  undefined value for error, "0 but true"
             for zero, or the actual return value otherwise.

     msgget(KEY,FLAGS)
             Calls the System V IPC function msgget.  Returns the
             message queue id, or the undefined value if there is
             an error.

     msgsnd(ID,MSG,FLAGS)
             Calls the System V IPC function msgsnd to  send  the
             message MSG to the message queue ID.  MSG must begin
             with the long integer message  type,  which  may  be
             created with pack("L", $type).  Returns true if suc-
             cessful, or false if there is an error.

     msgrcv(ID,VAR,SIZE,TYPE,FLAGS)
             Calls the System V IPC function msgrcv to receive  a
             message from message queue ID into variable VAR with
             a maximum message size of SIZE.  Note that if a mes-
             sage is received, the message type will be the first
             thing in VAR, and the maximum length of VAR is  SIZE
             plus  the size of the message type.  Returns true if
             successful, or false if there is an error.

     next LABEL
     next    The next command is like the continue  statement  in
             C; it starts the next iteration of the loop:

                  line: while (<STDIN>) {
                       next line if /^#/;  # discard comments
                       ...
                  }

             Note that if there were  a  continue  block  on  the
             above,  it  would  get  executed  even  on discarded
             lines.  If the LABEL is omitted, the command  refers
             to the innermost enclosing loop.

     oct(EXPR)
     oct EXPR
             Returns the decimal value of EXPR interpreted as  an
             octal  string.   (If  EXPR happens to start off with
             0x, interprets it as a hex string instead.) The fol-
             lowing  will  handle  decimal,  octal and hex in the
             standard notation:

                  $val = oct($val) if $val =~ /^0/;

             If EXPR is omitted, uses $_.

     open(FILEHANDLE,EXPR)
     open(FILEHANDLE)
     open FILEHANDLE
             Opens the file whose filename is given by EXPR,  and
             associates  it with FILEHANDLE.  If FILEHANDLE is an
             expression, its value is used as  the  name  of  the
             real  filehandle  wanted.   If  EXPR is omitted, the
             scalar variable of the same name as  the  FILEHANDLE
             contains  the filename.  If the filename begins with
             "<" or nothing, the file is opened  for  input.   If
             the filename begins with ">", the file is opened for
             output.  If the filename begins with ">>", the  file
             is  opened  for  appending.   (You  can put a '+' in
             front of the '>' or '<' to indicate  that  you  want
             both  read  and  write  access  to the file.) If the
             filename begins with "|",  the  filename  is  inter-
             preted  as a command to which output is to be piped,
             and if the filename ends with a "|", the filename is
             interpreted  as  command  which  pipes  input to us.
             (You may not have a command that pipes both  in  and
             out.) Opening '-' opens STDIN and opening '>-' opens
             STDOUT.  Open returns  non-zero  upon  success,  the
             undefined  value  otherwise.  If the open involved a
             pipe, the return value happens to be the pid of  the
             subprocess.  Examples:

                  $article = 100;
                  open article || die "Can't find article $article: $!\n";
                  while (<article>) {...

                  open(LOG, '>>/usr/spool/news/twitlog');
                                      # (log is reserved)

                  open(article, "caesar <$article |");
                                      # decrypt article

                  open(extract, "|sort >/tmp/Tmp$$");
                                      # $$ is our process#

                  # process argument list of files along with any includes

                  foreach $file (@ARGV) {
                       do process($file, 'fh00');    # no pun intended
                  }

                  sub process {
                       local($filename, $input) = @_;
                       $input++;      # this is a string increment
                       unless (open($input, $filename)) {
                            print STDERR "Can't open $filename: $!\n";
                            return;
                       }
                       while (<$input>) {       # note use of indirection
                            if (/^#include "(.*)"/) {
                                 do process($1, $input);
                                 next;
                            }
                            ...       # whatever

                       }
                  }

             You may also, in the Bourne shell tradition, specify
             an  EXPR beginning with ">&", in which case the rest
             of the string  is  interpreted  as  the  name  of  a
             filehandle (or file descriptor, if numeric) which is
             to be duped and opened.  You may use & after >,  >>,
             <,  +>,  +>>  and  +<.   The mode you specify should
             match the mode of the original filehandle.  Here  is
             a  script that saves, redirects, and restores STDOUT
             and STDERR:

                  #!/usr/bin/perl
                  open(SAVEOUT, ">&STDOUT");
                  open(SAVEERR, ">&STDERR");

                  open(STDOUT, ">foo.out") || die "Can't redirect stdout";
                  open(STDERR, ">&STDOUT") || die "Can't dup stdout";

                  select(STDERR); $| = 1;       # make unbuffered
                  select(STDOUT); $| = 1;       # make unbuffered

                  print STDOUT "stdout 1\n";    # this works for
                  print STDERR "stderr 1\n";    # subprocesses too

                  close(STDOUT);
                  close(STDERR);

                  open(STDOUT, ">&SAVEOUT");
                  open(STDERR, ">&SAVEERR");

                  print STDOUT "stdout 2\n";
                  print STDERR "stderr 2\n";

             If you open a pipe on the command "-",  i.e.  either
             "|-"  or  "-|", then there is an implicit fork done,
             and the return value of open is the pid of the child
             within  the  parent  process, and 0 within the child
             process.  (Use defined($pid)  to  determine  if  the
             open  was  successful.)  The filehandle behaves nor-
             mally for the parent, but i/o to that filehandle  is
             piped from/to the STDOUT/STDIN of the child process.
             In the child process the filehandle  isn't  opened--
             i/o  happens from/to the new STDOUT or STDIN.  Typi-
             cally this is used like the normal piped  open  when
             you  want to exercise more control over just how the
             pipe command gets executed, such  as  when  you  are
             running setuid, and don't want to have to scan shell
             commands for metacharacters.   The  following  pairs
             are more or less equivalent:

                  open(FOO, "|tr '[a-z]' '[A-Z]'");
                  open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';

                  open(FOO, "cat -n '$file'|");
                  open(FOO, "-|") || exec 'cat', '-n', $file;

             Explicitly closing any piped filehandle  causes  the
             parent  process to wait for the child to finish, and
             returns the status value in $?.  Note: on any opera-
             tion  which  may do a fork, unflushed buffers remain
             unflushed in both processes,  which  means  you  may
             need to set $| to avoid duplicate output.

             The filename that is passed to open will have  lead-
             ing  and  trailing  whitespace deleted.  In order to
             open a file with arbitrary weird characters  in  it,
             it's  necessary  to protect any leading and trailing
             whitespace thusly:

                     $file =~ s#^(\s)#./$1#;
                     open(FOO, "< $file\0");

     opendir(DIRHANDLE,EXPR)
             Opens a directory named EXPR for processing by read-
             dir(),   telldir(),   seekdir(),   rewinddir()   and
             closedir().  Returns true if successful.  DIRHANDLEs
             have their own namespace separate from FILEHANDLEs.

     ord(EXPR)
     ord EXPR
             Returns the numeric ascii value of the first charac-
             ter of EXPR.  If EXPR is omitted, uses $_.

     pack(TEMPLATE,LIST)
             Takes an array or list of values and packs it into a
             binary  structure,  returning  the string containing
             the structure.  The TEMPLATE is a sequence of  char-
             acters  that  give  the order and type of values, as
             follows:

                  A    An ascii string, will be space padded.
                  a    An ascii string, will be null padded.
                  c    A signed char value.
                  C    An unsigned char value.
                  s    A signed short value.
                  S    An unsigned short value.
                  i    A signed integer value.
                  I    An unsigned integer value.
                  l    A signed long value.
                  L    An unsigned long value.
                  n    A short in "network" order.
                  N    A long in "network" order.
                  f    A single-precision float in the native format.
                  d    A double-precision float in the native format.
                  p    A pointer to a string.
                  v    A short in "VAX" (little-endian) order.
                  V    A long in "VAX" (little-endian) order.
                  x    A null byte.
                  X    Back up a byte.
                  @    Null fill to absolute position.
                  u    A uuencoded string.
                  b    A bit string (ascending bit order, like vec()).
                  B    A bit string (descending bit order).
                  h    A hex string (low nybble first).
                  H    A hex string (high nybble first).

             Each letter may optionally be followed by  a  number
             which  gives  a repeat count.  With all types except
             "a", "A", "b", "B", "h" and "H", the  pack  function
             will  gobble up that many values from the LIST.  A *
             for the repeat count means to use however many items
             are  left.   The  "a"  and "A" types gobble just one
             value, but pack it as a string of length count, pad-
             ding  with  nulls  or  spaces  as  necessary.  (When
             unpacking, "A" strips trailing spaces and nulls, but
             "a" does not.) Likewise, the "b" and "B" fields pack
             a string that many  bits  long.   The  "h"  and  "H"
             fields  pack  a string that many nybbles long.  Real
             numbers (floats  and  doubles)  are  in  the  native
             machine  format  only;  due  to  the multiplicity of
             floating formats around, and the lack of a  standard
             "network"  representation,  no  facility  for inter-
             change has been made.  This means that packed float-
             ing  point  data  written  on one machine may not be
             readable on another - even if both use IEEE floating
             point  arithmetic  (as the endian-ness of the memory
             representation is not part of the IEEE spec).   Note
             that  perl  uses  doubles internally for all numeric
             calculation, and converting from double -> float  ->
             double   will   lose   precision  (i.e.  unpack("f",
             pack("f", $foo)) will not in general equal $foo).
             Examples:

                  $foo = pack("cccc",65,66,67,68);
                  # foo eq "ABCD"
                  $foo = pack("c4",65,66,67,68);
                  # same thing

                  $foo = pack("ccxxcc",65,66,67,68);
                  # foo eq "AB\0\0CD"

                  $foo = pack("s2",1,2);

                  # "\1\0\2\0" on little-endian
                  # "\0\1\0\2" on big-endian

                  $foo = pack("a4","abcd","x","y","z");
                  # "abcd"

                  $foo = pack("aaaa","abcd","x","y","z");
                  # "axyz"

                  $foo = pack("a14","abcdefg");
                  # "abcdefg\0\0\0\0\0\0\0"

                  $foo = pack("i9pl", gmtime);
                  # a real struct tm (on my system anyway)

                  sub bintodec {
                      unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
                  }
             The same template may generally also be used in  the
             unpack function.

     pipe(READHANDLE,WRITEHANDLE)
             Opens a pair of connected pipes like the correspond-
             ing  system call.  Note that if you set up a loop of
             piped processes, deadlock can occur unless  you  are
             very  careful.   In addition, note that perl's pipes
             use stdio buffering, so you may need to  set  $|  to
             flush your WRITEHANDLE after each command, depending
             on   the   application.    [Requires   version   3.0
             patchlevel 9.]

     pop(ARRAY)
     pop ARRAY
             Pops and returns the last value of the array,  shor-
             tening the array by 1.  Has the same effect as

                  $tmp = $ARRAY[$#ARRAY--];

             If there are no elements in the array,  returns  the
             undefined value.

     print(FILEHANDLE LIST)
     print(LIST)
     print FILEHANDLE LIST
     print LIST
     print   Prints  a  string  or  a  comma-separated  list   of
             strings.     Returns    non-zero    if   successful.
             FILEHANDLE may be a scalar variable name,  in  which
             case  the variable contains the name of the filehan-
             dle, thus  introducing  one  level  of  indirection.
             (NOTE:  If  FILEHANDLE  is  a  variable and the next
             token is a term, it  may  be  misinterpreted  as  an
             operator  unless  you  interpose  a  + or put parens
             around the arguments.)  If  FILEHANDLE  is  omitted,
             prints by default to standard output (or to the last
             selected output channel--see select()).  If LIST  is
             also  omitted,  prints  $_  to  STDOUT.   To set the
             default  output  channel  to  something  other  than
             STDOUT use the select operation.  Note that, because
             print  takes  a  LIST,  anything  in  the  LIST   is
             evaluated  in  an  array context, and any subroutine
             that you call will have one or more of  its  expres-
             sions  evaluated in an array context.  Also be care-
             ful not to follow the  print  keyword  with  a  left
             parenthesis  unless you want the corresponding right
             parenthesis  to  terminate  the  arguments  to   the
             print--interpose  a  +  or put parens around all the
             arguments.

     printf(FILEHANDLE LIST)
     printf(LIST)
     printf FILEHANDLE LIST
     printf LIST
             Equivalent to a "print FILEHANDLE sprintf(LIST)".

     push(ARRAY,LIST)
             Treats ARRAY (@ is optional) as a stack, and  pushes
             the  values  of  LIST  onto  the  end of ARRAY.  The
             length of ARRAY increases by  the  length  of  LIST.
             Has the same effect as

                 for $value (LIST) {
                      $ARRAY[++$#ARRAY] = $value;
                 }

             but is more efficient.

     q/STRING/
     qq/STRING/
     qx/STRING/
             These are not really functions, but simply syntactic
             sugar  to let you avoid putting too many backslashes
             into quoted strings.  The q operator is  a  general-
             ized single quote, and the qq operator a generalized
             double quote.  The  qx  operator  is  a  generalized
             backquote.   Any  non-alphanumeric  delimiter can be
             used in place of /, including newline.  If the  del-
             imiter  is  an  opening  bracket or parenthesis, the
             final delimiter will be  the  corresponding  closing
             bracket  or  parenthesis.   (Embedded occurrences of
             the  closing  bracket  need  to  be  backslashed  as
             usual.) Examples:

                  $foo = q!I said, "You said, 'She said it.'"!;
                  $bar = q('This is it.');
                  $today = qx{ date };
                  $_ .= qq
             *** The previous line contains the naughty word "$&".\n
                       if /(ibm|apple|awk)/;      # :-)

     rand(EXPR)
     rand EXPR
     rand    Returns a random fractional number between 0 and the
             value  of  EXPR.  (EXPR should be positive.) If EXPR
             is omitted, returns a value between 0  and  1.   See
             also srand().

     read(FILEHANDLE,SCALAR,LENGTH,OFFSET)
     read(FILEHANDLE,SCALAR,LENGTH)
             Attempts to read LENGTH bytes of data into  variable
             SCALAR  from  the specified FILEHANDLE.  Returns the
             number of bytes actually read, or undef if there was
             an  error.   SCALAR  will  be grown or shrunk to the
             length actually read.  An OFFSET may be specified to
             place  the  read  data  at some other place than the
             beginning of the  string.   This  call  is  actually
             implemented  in terms of stdio's fread call.  To get
             a true read system call, see sysread.

     readdir(DIRHANDLE)
     readdir DIRHANDLE
             Returns the next directory  entry  for  a  directory
             opened  by  opendir().  If used in an array context,
             returns all the rest of the entries  in  the  direc-
             tory.   If  there  are  no  more entries, returns an
             undefined value in a scalar context or a  null  list
             in an array context.

     readlink(EXPR)
     readlink EXPR
             Returns the value of a symbolic  link,  if  symbolic
             links are implemented.  If not, gives a fatal error.
             If there is some system error, returns the undefined
             value and sets $! (errno).  If EXPR is omitted, uses
             $_.

     recv(SOCKET,SCALAR,LEN,FLAGS)
             Receives a message on a socket.  Attempts to receive
             LENGTH  bytes  of data into variable SCALAR from the
             specified SOCKET filehandle.  Returns the address of
             the  sender,  or  the  undefined value if there's an
             error.  SCALAR will be grown or shrunk to the length
             actually  read.   Takes the same flags as the system
             call of the same name.

     redo LABEL
     redo    The redo command restarts  the  loop  block  without
             evaluating  the  conditional  again.   The  continue
             block, if any, is not executed.   If  the  LABEL  is
             omitted, the command refers to the innermost enclos-
             ing loop.  This command is normally used by programs
             that  want  to lie to themselves about what was just
             input:

                  # a simpleminded Pascal comment stripper
                  # (warning: assumes no { or } in strings)
                  line: while (<STDIN>) {
                       while (s|({.*}.*){.*}|$1 |) {}
                       s|{.*}| |;
                       if (s|{.*| |) {
                            $front = $_;
                            while (<STDIN>) {
                                 if (/}/) {     # end of comment?
                                      s|^|$front{|;
                                      redo line;
                                 }
                            }
                       }
                       print;
                  }

     rename(OLDNAME,NEWNAME)
             Changes the name of a file.  Returns 1 for  success,
             0  otherwise.  Will not work across filesystem boun-
             daries.

     require(EXPR)
     require EXPR
     require Includes the library file specified by EXPR,  or  by
             $_  if  EXPR is not supplied.  Has semantics similar
             to the following subroutine:

                  sub require {
                      local($filename) = @_;
                      return 1 if $INC{$filename};
                      local($realfilename,$result);
                      ITER: {
                       foreach $prefix (@INC) {
                           $realfilename = "$prefix/$filename";
                           if (-f $realfilename) {
                            $result = do $realfilename;
                            last ITER;
                           }
                       }
                       die "Can't find $filename in \@INC";
                      }
                      die $@ if $@;
                      die "$filename did not return true value" unless $result;
                      $INC{$filename} = $realfilename;
                      $result;
                  }

             Note that the file will not be included twice  under
             the same specified name.

     reset(EXPR)
     reset EXPR
     reset   Generally used in a continue block at the end  of  a
             loop  to  clear  variables  and reset ?? searches so
             that they work again.  The expression is interpreted
             as  a list of single characters (hyphens allowed for
             ranges).  All variables and  arrays  beginning  with
             one  of  those  letters  are reset to their pristine
             state.  If  the  expression  is  omitted,  one-match
             searches (?pattern?) are reset to match again.  Only
             resets variables or searches in the current package.
             Always returns 1.  Examples:

                 reset 'X';      # reset all X variables
                 reset 'a-z';    # reset lower case variables
                 reset;          # just reset ?? searches

             Note:  resetting  "A-Z"  is  not  recommended  since
             you'll wipe out your ARGV and ENV arrays.

             The use of reset on dbm associative arrays does  not
             change  the  dbm file.  (It does, however, flush any
             entries cached by perl, which may be useful  if  you
             are sharing the dbm file.  Then again, maybe not.)

     return LIST
             Returns from a subroutine with the value  specified.
             (Note that a subroutine can automatically return the
             value of the last expression evaluated.  That's  the
             preferred method--use of an explicit return is a bit
             slower.)

     reverse(LIST)
     reverse LIST
             In an array context, returns an array value consist-
             ing  of  the elements of LIST in the opposite order.
             In a scalar context, returns a string value consist-
             ing of the bytes of the first element of LIST in the
             opposite order.

     rewinddir(DIRHANDLE)
     rewinddir DIRHANDLE
             Sets the current position to the  beginning  of  the
             directory for the readdir() routine on DIRHANDLE.

     rindex(STR,SUBSTR,POSITION)
     rindex(STR,SUBSTR)
             Works just like index except  that  it  returns  the
             position  of  the  LAST occurrence of SUBSTR in STR.
             If  POSITION  is   specified,   returns   the   last
             occurrence at or before that position.

     rmdir(FILENAME)
     rmdir FILENAME
             Deletes the directory specified by FILENAME if it is
             empty.   If  it  succeeds it returns 1, otherwise it
             returns 0 and sets $! (errno).  If FILENAME is omit-
             ted, uses $_.

     s/PATTERN/REPLACEMENT/gieo
             Searches a string  for  a  pattern,  and  if  found,
             replaces  that pattern with the replacement text and
             returns the number of substitutions made.  Otherwise
             it  returns  false (0).  The "g" is optional, and if
             present, indicates that all occurrences of the  pat-
             tern  are to be replaced.  The "i" is also optional,
             and if present, indicates that  matching  is  to  be
             done  in  a  case-insensitive  manner.   The  "e" is
             likewise optional, and if  present,  indicates  that
             the  replacement  string  is  to  be evaluated as an
             expression  rather  than  just  as  a  double-quoted
             string.   Any non-alphanumeric delimiter may replace
             the slashes; if single quotes are used, no interpre-
             tation  is  done  on  the  replacement string (the e
             modifier overrides this, however); if backquotes are
             used, the replacement string is a command to execute
             whose output will be used as the actual  replacement
             text.   If  no  string is specified via the =~ or !~
             operator, the $_ string is  searched  and  modified.
             (The string specified with =~ must be a scalar vari-
             able, an array element, or an assignment to  one  of
             those,  i.e. an lvalue.) If the pattern contains a $
             that looks like a variable rather  than  an  end-of-
             string  test, the variable will be interpolated into
             the pattern at run-time.  If you only want the  pat-
             tern  compiled  once  the first time the variable is
             interpolated, add an "o" at the end.  If the PATTERN
             evaluates to a null string, the most recent success-
             ful regular expression is used  instead.   See  also
             the section on regular expressions.  Examples:

                 s/\bgreen\b/mauve/g;      # don't change wintergreen

                 $path =~ s|/usr/bin|/usr/local/bin|;

                 s/Login: $foo/Login: $bar/; # run-time pattern

                 ($foo = $bar) =~ s/bar/foo/;

                 $_ = 'abc123xyz';
                 s/\d+/$&*2/e;        # yields 'abc246xyz'
                 s/\d+/sprintf("%5d",$&)/e;     # yields 'abc  246xyz'
                 s/\w/$& x 2/eg;      # yields 'aabbcc  224466xxyyzz'

                 s/([^ ]*) *([^ ]*)/$2 $1/;     # reverse 1st two fields

             (Note the use of $ instead of \ in the last example.
             See section on Regular Expressions.)

     scalar(EXPR)
             Forces EXPR to be interpreted in  a  scalar  context
             and returns the value of EXPR.

     seek(FILEHANDLE,POSITION,WHENCE)
             Randomly positions the file pointer for  FILEHANDLE,
             just like the fseek() call of stdio.  FILEHANDLE may
             be an expression whose value gives the name  of  the
             filehandle.  Returns 1 upon success, 0 otherwise.

     seekdir(DIRHANDLE,POS)
             Sets the current position for the readdir()  routine
             on  DIRHANDLE.   POS  must  be  a  value returned by
             telldir().  Has  the  same  caveats  about  possible
             directory  compaction  as  the  corresponding system
             library routine.

     select(FILEHANDLE)
     select  Returns the currently selected filehandle.  Sets the
             current default filehandle for output, if FILEHANDLE
             is supplied.  This has two effects: first,  a  write
             or a print without a filehandle will default to this
             FILEHANDLE.  Second, references to variables related
             to  output  will  refer to this output channel.  For
             example, if you have to set the top of  form  format
             for  more  than one output channel, you might do the
             following:

                  select(REPORT1);
                  $^ = 'report1_top';
                  select(REPORT2);
                  $^ = 'report2_top';

             FILEHANDLE may be an expression  whose  value  gives
             the name of the actual filehandle.  Thus:

                  $oldfh = select(STDERR); $| = 1; select($oldfh);

     select(RBITS,WBITS,EBITS,TIMEOUT)
             This calls the select system call with the  bitmasks
             specified,  which  can be constructed using fileno()
             and vec(), along these lines:

                  $rin = $win = $ein = '';
                  vec($rin,fileno(STDIN),1) = 1;
                  vec($win,fileno(STDOUT),1) = 1;
                  $ein = $rin | $win;

             If you want to select on many filehandles you  might
             wish to write a subroutine:

                  sub fhbits {
                      local(@fhlist) = split(' ',$_[0]);
                      local($bits);
                      for (@fhlist) {
                       vec($bits,fileno($_),1) = 1;
                      }
                      $bits;
                  }
                  $rin = &fhbits('STDIN TTY SOCK');

             The usual idiom is:

                  ($nfound,$timeleft) =
                    select($rout=$rin, $wout=$win, $eout=$ein, $timeout);

             or to block until something becomes ready:

                  $nfound = select($rout=$rin, $wout=$win,
                                 $eout=$ein, undef);

             Any of the bitmasks can also be undef.  The timeout,
             if  specified,  is  in  seconds,  which may be frac-
             tional.  NOTE: not all implementations  are  capable
             of  returning  the  $timeleft.   If not, they always
             return $timeleft equal to the supplied $timeout.

     semctl(ID,SEMNUM,CMD,ARG)
             Calls the System V IPC function semctl.  If  CMD  is
             &IPC_STAT  or  &GETALL,  then ARG must be a variable
             which will hold the returned semid_ds  structure  or
             semaphore  value  array.   Returns  like  ioctl: the
             undefined value for error, "0 but true" for zero, or
             the actual return value otherwise.

     semget(KEY,NSEMS,SIZE,FLAGS)
             Calls the System V IPC function semget.  Returns the
             semaphore  id, or the undefined value if there is an
             error.

     semop(KEY,OPSTRING)
             Calls the System V IPC  function  semop  to  perform
             semaphore  operations such as signaling and waiting.
             OPSTRING must be a packed array of semop structures.
             Each   semop   structure   can   be  generated  with
             'pack("sss",  $semnum,  $semop,   $semflag)'.    The
             number  of  semaphore  operations  is implied by the
             length of OPSTRING.  Returns true if successful,  or
             false if there is an error.  As an example, the fol-
             lowing code waits on semaphore $semnum of  semaphore
             id $semid:

                  $semop = pack("sss", $semnum, -1, 0);
                  die "Semaphore trouble: $!\n" unless semop($semid, $semop);

             To signal the semaphore, replace "-1" with "1".

     send(SOCKET,MSG,FLAGS,TO)
     send(SOCKET,MSG,FLAGS)
             Sends a message on a socket.  Takes the  same  flags
             as the system call of the same name.  On unconnected
             sockets you must specify a destination to  send  TO.
             Returns  the number of characters sent, or the unde-
             fined value if there is an error.

     setpgrp(PID,PGRP)
             Sets the current process  group  for  the  specified
             PID,  0  for  the  current  process.  Will produce a
             fatal error if used on a machine that doesn't imple-
             ment setpgrp(2).

     setpriority(WHICH,WHO,PRIORITY)
             Sets the current priority for a process,  a  process
             group,  or  a user.  (See setpriority(2).) Will pro-
             duce a fatal error if used on a machine that doesn't
             implement setpriority(2).

     setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)
             Sets the socket option requested.  Returns undefined
             if  there  is  an error.  OPTVAL may be specified as
             undef if you don't want to pass an argument.

     shift(ARRAY)
     shift ARRAY
     shift   Shifts the first value of the array off and  returns
             it,  shortening the array by 1 and moving everything
             down.  If  there  are  no  elements  in  the  array,
             returns  the  undefined value.  If ARRAY is omitted,
             shifts the @ARGV array in the main program, and  the
             @_  array in subroutines.  (This is determined lexi-
             cally.)  See  also  unshift(),  push()  and   pop().
             Shift()  and unshift() do the same thing to the left
             end of an array that push()  and  pop()  do  to  the
             right end.

     shmctl(ID,CMD,ARG)
             Calls the System V IPC function shmctl.  If  CMD  is
             &IPC_STAT,  then  ARG  must be a variable which will
             hold the returned shmid_ds structure.  Returns  like
             ioctl:  the  undefined value for error, "0 but true"
             for zero, or the actual return value otherwise.

     shmget(KEY,SIZE,FLAGS)
             Calls the System V IPC function shmget.  Returns the
             shared  memory segment id, or the undefined value if
             there is an error.

     shmread(ID,VAR,POS,SIZE)
     shmwrite(ID,STRING,POS,SIZE)
             Reads or writes the System V shared  memory  segment
             ID  starting  at  position  POS  for  size  SIZE  by
             attaching to it, copying in/out, and detaching  from
             it.  When reading, VAR must be a variable which will
             hold the data read.  When writing, if STRING is  too
             long,  only  SIZE  bytes  are used; if STRING is too
             short, nulls are written to  fill  out  SIZE  bytes.
             Return  true  if successful, or false if there is an
             error.

     shutdown(SOCKET,HOW)
             Shuts down a socket connection in the  manner  indi-
             cated  by  HOW, which has the same interpretation as
             in the system call of the same name.

     sin(EXPR)
     sin EXPR
             Returns the sine of EXPR (expressed in radians).  If
             EXPR is omitted, returns sine of $_.

     sleep(EXPR)
     sleep EXPR
     sleep   Causes the script to sleep for EXPR seconds, or for-
             ever  if no EXPR.  May be interrupted by sending the
             process a SIGALRM.  Returns the  number  of  seconds
             actually slept.  You probably cannot mix alarm() and
             sleep() calls, since sleep()  is  often  implemented
             using alarm().

     socket(SOCKET,DOMAIN,TYPE,PROTOCOL)
             Opens a socket of the specified kind and attaches it
             to filehandle SOCKET.  DOMAIN, TYPE and PROTOCOL are
             specified the same as for the  system  call  of  the
             same name.  You may need to run h2ph on sys/socket.h
             to get the proper values handy  in  a  perl  library
             file.   Return  true if successful.  See the example
             in the section on Interprocess Communication.

     socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)
             Creates an unnamed pair of sockets in the  specified
             domain,  of  the  specified  type.  DOMAIN, TYPE and
             PROTOCOL are specified the same as  for  the  system
             call  of  the same name.  If unimplemented, yields a
             fatal error.  Return true if successful.

     sort(SUBROUTINE LIST)
     sort(LIST)
     sort SUBROUTINE LIST
     sort BLOCK LIST
     sort LIST
             Sorts the LIST and returns the sorted  array  value.
             Nonexistent  values  of arrays are stripped out.  If
             SUBROUTINE or BLOCK is omitted,  sorts  in  standard
             string  comparison  order.   If SUBROUTINE is speci-
             fied, gives the name of a subroutine that returns an
             integer  less  than,  equal  to,  or greater than 0,
             depending on how the elements of the array are to be
             ordered.   (The  <=> and cmp operators are extremely
             useful in such routines.) SUBROUTINE may be a scalar
             variable  name, in which case the value provides the
             name of the subroutine to use.  In place of  a  SUB-
             ROUTINE   name,  you  can  provide  a  BLOCK  as  an
             anonymous, in-line sort subroutine.

             In the interests of efficiency  the  normal  calling
             code for subroutines is bypassed, with the following
             effects: the subroutine may not be a recursive  sub-
             routine,  and  the  two  elements to be compared are
             passed into the subroutine not via @_ but as $a  and
             $b  (see  example below).  They are passed by refer-
             ence so don't modify $a and $b.

             Examples:

                  # sort lexically
                  @articles = sort @files;

                  # same thing, but with explicit sort routine
                  @articles = sort {$a cmp $b;} @files;

                  # same thing in reversed order
                  @articles = sort {$b cmp $a;} @files;

                  # sort numerically ascending
                  @articles = sort {$a <=> $b;} @files;

                  # sort numerically descending
                  @articles = sort {$b <=> $a;} @files;

                  # sort using explicit subroutine name
                  sub byage {
                      $age{$a} <=> $age{$b};    # presuming integers
                  }
                  @sortedclass = sort byage @class;

                  sub reverse { $b cmp $a; }
                  @harry = ('dog','cat','x','Cain','Abel');
                  @george = ('gone','chased','yz','Punished','Axed');
                  print sort @harry;
                       # prints AbelCaincatdogx
                  print sort reverse @harry;
                       # prints xdogcatCainAbel
                  print sort @george, 'to', @harry;
                       # prints AbelAxedCainPunishedcatchaseddoggonetoxyz

     splice(ARRAY,OFFSET,LENGTH,LIST)
     splice(ARRAY,OFFSET,LENGTH)
     splice(ARRAY,OFFSET)
             Removes the elements designated by OFFSET and LENGTH
             from  an  array, and replaces them with the elements
             of LIST, if any.  Returns the elements removed  from
             the array.  The array grows or shrinks as necessary.
             If LENGTH is omitted, removes everything from OFFSET
             onward.   The following equivalencies hold (assuming
             $[ == 0):

                  push(@a,$x,$y)                splice(@a,$#a+1,0,$x,$y)
                  pop(@a)                       splice(@a,-1)
                  shift(@a)                     splice(@a,0,1)
                  unshift(@a,$x,$y)             splice(@a,0,0,$x,$y)
                  $a[$x] = $y                   splice(@a,$x,1,$y);

             Example, assuming array lengths are passed before arrays:

                  sub aeq { # compare two array values
                       local(@a) = splice(@_,0,shift);
                       local(@b) = splice(@_,0,shift);
                       return 0 unless @a == @b;     # same len?
                       while (@a) {
                           return 0 if pop(@a) ne pop(@b);
                       }
                       return 1;
                  }
                  if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }

     split(/PATTERN/,EXPR,LIMIT)
     split(/PATTERN/,EXPR)
     split(/PATTERN/)
     split   Splits a  string  into  an  array  of  strings,  and
             returns  it.   (If  not in an array context, returns
             the number of fields found and splits  into  the  @_
             array.   (In  an  array  context,  you can force the
             split into @_ by using ?? as the pattern delimiters,
             but  it  still returns the array value.)) If EXPR is
             omitted, splits the $_ string.  If PATTERN  is  also
             omitted,  splits  on  whitespace (/[ \t\n]+/).  Any-
             thing matching PATTERN is taken to  be  a  delimiter
             separating the fields.  (Note that the delimiter may
             be longer than one character.) If  LIMIT  is  speci-
             fied,  splits  into  no  more  than that many fields
             (though it may  split  into  fewer).   If  LIMIT  is
             unspecified,   trailing  null  fields  are  stripped
             (which potential users of pop()  would  do  well  to
             remember).   A pattern matching the null string (not
             to be confused with a null pattern //, which is just
             one  member  of  the set of patterns matching a null
             string) will split the value of EXPR  into  separate
             characters  at  each point it matches that way.  For
             example:

                  print join(':', split(/ */, 'hi there'));

             produces the output 'h:i:t:h:e:r:e'.

             The LIMIT parameter can be used to partially split a
             line

                  ($login, $passwd, $remainder) = split(/:/, $_, 3);

             (When assigning to a list, if LIMIT is omitted, perl
             supplies a LIMIT one larger than the number of vari-
             ables in the list, to avoid unnecessary  work.   For
             the  list  above LIMIT would have been 4 by default.
             In time critical applications it behooves you not to
             split into more fields than you really need.)

             If  the  PATTERN  contains  parentheses,  additional
             array  elements  are created from each matching sub-
             string in the delimiter.

                  split(/([,-])/,"1-10,20");

             produces the array value

                  (1,'-',10,',',20)

             The  pattern  /PATTERN/  may  be  replaced  with  an
             expression to specify patterns that vary at runtime.
             (To  do   runtime   compilation   only   once,   use
             /$variable/o.) As a special case, specifying a space
             (' ') will split on white space just as  split  with
             no  arguments does, but leading white space does NOT
             produce a null first field.  Thus, split(' ') can be
             used  to  emulate  awk's  default  behavior, whereas
             split(/ /) will give you as many null initial fields
             as there are leading spaces.

             Example:

                  open(passwd, '/etc/passwd');
                  while (<passwd>) {
                       ($login, $passwd, $uid, $gid, $gcos, $home, $shell)
                            = split(/:/);
                       ...
                  }

             (Note that $shell above will still have a newline on
             it.  See chop().) See also join.

     sprintf(FORMAT,LIST)
             Returns a string formatted by the usual printf  con-
             ventions.  The * character is not supported.

     sqrt(EXPR)
     sqrt EXPR
             Return the square root of EXPR.  If EXPR is omitted,
             returns square root of $_.

     srand(EXPR)
     srand EXPR
             Sets the random number seed for the  rand  operator.
             If EXPR is omitted, does srand(time).

     stat(FILEHANDLE)
     stat FILEHANDLE
     stat(EXPR)
     stat SCALARVARIABLE
             Returns a 13-element array giving the statistics for
             a  file,  either  the file opened via FILEHANDLE, or
             named by EXPR.  Typically used as follows:

                 ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
                    $atime,$mtime,$ctime,$blksize,$blocks)
                        = stat($filename);

             If stat is passed the special filehandle  consisting
             of  an  underline,  no stat is done, but the current
             contents of the stat structure from the last stat or
             filetest are returned.  Example:

                  if (-x $file && (($d) = stat(_)) && $d < 0) {
                       print "$file is executable NFS file\n";
                  }

             (This only works on machines for  which  the  device
             number is negative under NFS.)

     study(SCALAR)
     study SCALAR
     study   Takes extra time to study SCALAR ($_ if unspecified)
             in anticipation of doing many pattern matches on the
             string before it is next modified.  This may or  may
             not save time, depending on the nature and number of
             patterns you are searching on, and on the  distribu-
             tion  of  character  frequencies in the string to be
             searched--you probably want to compare runtimes with
             and  without  it  to  see  which runs faster.  Those
             loops which scan for  many  short  constant  strings
             (including  the  constant parts of more complex pat-
             terns) will benefit most.  You  may  have  only  one
             study  active  at  a  time--if you study a different
             scalar the first is  "unstudied".   (The  way  study
             works  is  this: a linked list of every character in
             the string to be searched is made, so we  know,  for
             example,  where  all  the  'k' characters are.  From
             each  search  string,  the   rarest   character   is
             selected, based on some static frequency tables con-
             structed from some  C  programs  and  English  text.
             Only those places that contain this "rarest" charac-
             ter are examined.)

             For example, here is a loop which inserts index pro-
             ducing  entries before any line containing a certain
             pattern:

                  while (<>) {
                       study;
                       print ".IX foo\n" if /\bfoo\b/;
                       print ".IX bar\n" if /\bbar\b/;
                       print ".IX blurfl\n" if /\bblurfl\b/;
                       ...
                       print;
                  }

             In searching for /\bfoo\b/, only those locations  in
             $_  that  contain 'f' will be looked at, because 'f'
             is rarer than 'o'.  In general, this is  a  big  win
             except  in pathological cases.  The only question is
             whether it saves you more time than it took to build
             the linked list in the first place.

             Note that if you have to look for strings  that  you
             don't  know  till  runtime,  you can build an entire
             loop as a string and eval that to avoid  recompiling
             all your patterns all the time.  Together with unde-
             fining $/ to input entire files as one record,  this
             can be very fast, often faster than specialized pro-
             grams like fgrep.  The following  scans  a  list  of
             files  (@files)  for  a  list of words (@words), and
             prints out the names of those files that  contain  a
             match:

                  $search = 'while (<>) { study;';
                  foreach $word (@words) {
                      $search .= "++\$seen{\$ARGV} if /\b$word\b/;\n";
                  }
                  $search .= "}";
                  @ARGV = @files;
                  undef $/;
                  eval $search;       # this screams
                  $/ = "\n";          # put back to normal input delim
                  foreach $file (sort keys(%seen)) {
                      print $file, "\n";
                  }

     substr(EXPR,OFFSET,LEN)
     substr(EXPR,OFFSET)
             Extracts a substring out of  EXPR  and  returns  it.
             First  character  is at offset 0, or whatever you've
             set $[ to.  If OFFSET is negative, starts  that  far
             from  the  end  of  the  string.  If LEN is omitted,
             returns everything to the end of  the  string.   You
             can use the substr() function as an lvalue, in which
             case EXPR must be an lvalue.  If  you  assign  some-
             thing  shorter than LEN, the string will shrink, and
             if you assign something longer than LEN, the  string
             will grow to accommodate it.  To keep the string the
             same length you may need to pad or chop  your  value
             using sprintf().

     symlink(OLDFILE,NEWFILE)
             Creates a new filename symbolically  linked  to  the
             old  filename.   Returns 1 for success, 0 otherwise.
             On systems that don't support symbolic  links,  pro-
             duces a fatal error at run time.  To check for that,
             use eval:

                  $symlink_exists = (eval 'symlink("","");', $@ eq '');

     syscall(LIST)
     syscall LIST
             Calls the system call specified as the first element
             of the list, passing the remaining elements as argu-
             ments to the system call.   If  unimplemented,  pro-
             duces  a fatal error.  The arguments are interpreted
             as follows: if a  given  argument  is  numeric,  the
             argument  is  passed as an int.  If not, the pointer
             to the string value is passed.  You are  responsible
             to make sure a string is pre-extended long enough to
             receive any result that  might  be  written  into  a
             string.   If your integer arguments are not literals
             and have never been interpreted in  a  numeric  con-
             text, you may need to add 0 to them to force them to
             look like numbers.

                  require 'syscall.ph';         # may need to run h2ph
                  syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9);

     sysread(FILEHANDLE,SCALAR,LENGTH,OFFSET)
     sysread(FILEHANDLE,SCALAR,LENGTH)
             Attempts to read LENGTH bytes of data into  variable
             SCALAR from the specified FILEHANDLE, using the sys-
             tem call read(2).  It bypasses stdio, so mixing this
             with  other  kinds  of  reads  may  cause confusion.
             Returns the number of bytes actually read, or  undef
             if  there  was  an  error.   SCALAR will be grown or
             shrunk to the length actually read.  An  OFFSET  may
             be  specified  to  place the read data at some other
             place than the beginning of the string.

     system(LIST)
     system LIST
             Does exactly the same thing as  "exec  LIST"  except
             that  a  fork  is done first, and the parent process
             waits for the child process to complete.  Note  that
             argument  processing  varies depending on the number
             of arguments.  The return value is the  exit  status
             of  the  program as returned by the wait() call.  To
             get the actual exit value divide by 256.   See  also
             exec.

     syswrite(FILEHANDLE,SCALAR,LENGTH,OFFSET)
     syswrite(FILEHANDLE,SCALAR,LENGTH)
             Attempts to write LENGTH bytes of data from variable
             SCALAR to the specified FILEHANDLE, using the system
             call write(2).  It bypasses stdio,  so  mixing  this
             with prints may cause confusion.  Returns the number
             of bytes actually written, or undef if there was  an
             error.  An OFFSET may be specified to place the read
             data at some other place than the beginning  of  the
             string.

     tell(FILEHANDLE)
     tell FILEHANDLE
     tell    Returns the current file  position  for  FILEHANDLE.
             FILEHANDLE  may  be  an expression whose value gives
             the name of the actual filehandle.  If FILEHANDLE is
             omitted, assumes the file last read.

     telldir(DIRHANDLE)
     telldir DIRHANDLE
             Returns the current position of the  readdir()  rou-
             tines on DIRHANDLE.  Value may be given to seekdir()
             to access a particular location in a directory.  Has
             the same caveats about possible directory compaction
             as the corresponding system library routine.

     time    Returns  the  number  of  non-leap   seconds   since
             00:00:00 UTC, January 1, 1970.  Suitable for feeding
             to gmtime() and localtime().

     times   Returns a four-element array  giving  the  user  and
             system  times,  in seconds, for this process and the
             children of this process.

                 ($user,$system,$cuser,$csystem) = times;

     tr/SEARCHLIST/REPLACEMENTLIST/cds
     y/SEARCHLIST/REPLACEMENTLIST/cds
             Translates all occurrences of the  characters  found
             in  the search list with the corresponding character
             in the replacement list.  It returns the  number  of
             characters  replaced  or  deleted.   If no string is
             specified via the =~ or !~ operator, the  $_  string
             is  translated.   (The string specified with =~ must
             be a  scalar  variable,  an  array  element,  or  an
             assignment to one of those, i.e. an lvalue.) For sed
             devotees, y is provided as a synonym for tr.

             If the c modifier is specified, the SEARCHLIST char-
             acter  set  is  complemented.   If the d modifier is
             specified, any characters  specified  by  SEARCHLIST
             that  are  not found in REPLACEMENTLIST are deleted.
             (Note that this is slightly more flexible  than  the
             behavior  of some tr programs, which delete anything
             they find in  the  SEARCHLIST,  period.)  If  the  s
             modifier  is specified, sequences of characters that
             were translated to the same character  are  squashed
             down to 1 instance of the character.

             If the d modifier was used, the  REPLACEMENTLIST  is
             always interpreted exactly as specified.  Otherwise,
             if the REPLACEMENTLIST is  shorter  than  the  SEAR-
             CHLIST, the final character is replicated till it is
             long enough.  If the REPLACEMENTLIST  is  null,  the
             SEARCHLIST is replicated.  This latter is useful for
             counting characters in a  class,  or  for  squashing
             character sequences in a class.

             Examples:

                 $ARGV[1] =~ y/A-Z/a-z/;   # canonicalize to lower case

                 $cnt = tr/*/*/;           # count the stars in $_

                 $cnt = tr/0-9//;          # count the digits in $_

                 tr/a-zA-Z//s;             # bookkeeper -> bokeper

                 ($HOST = $host) =~ tr/a-z/A-Z/;

                 y/a-zA-Z/ /cs;            # change non-alphas to single space

                 tr/\200-\377/\0-\177/;    # delete 8th bit

     truncate(FILEHANDLE,LENGTH)
     truncate(EXPR,LENGTH)
             Truncates the file opened on FILEHANDLE, or named by
             EXPR,  to  the  specified  length.  Produces a fatal
             error if truncate isn't implemented on your system.

     umask(EXPR)
     umask EXPR
     umask   Sets the umask for the process and returns  the  old
             one.   If  EXPR  is  omitted, merely returns current
             umask.

     undef(EXPR)
     undef EXPR
     undef   Undefines the  value  of  EXPR,  which  must  be  an
             lvalue.   Use  only  on  a  scalar  value, an entire
             array, or a subroutine name (using &).  (Undef  will
             probably  not  do what you expect on most predefined
             variables or dbm array values.) Always  returns  the
             undefined  value.   You  can omit the EXPR, in which
             case nothing is undefined,  but  you  still  get  an
             undefined value that you could, for instance, return
             from a subroutine.  Examples:

                  undef $foo;
                  undef $bar{'blurfl'};
                  undef @ary;
                  undef %assoc;
                  undef &mysub;
                  return (wantarray ? () : undef) if $they_blew_it;

     unlink(LIST)
     unlink LIST
             Deletes a list of  files.   Returns  the  number  of
             files successfully deleted.

                  $cnt = unlink 'a', 'b', 'c';
                  unlink @goners;
                  unlink <*.bak>;

             Note: unlink will not delete directories unless  you
             are  superuser  and the -U flag is supplied to perl.
             Even if these conditions are  met,  be  warned  that
             unlinking  a  directory  can  inflict damage on your
             filesystem.  Use rmdir instead.

     unpack(TEMPLATE,EXPR)
             Unpack does the reverse of pack: it takes  a  string
             representing  a structure and expands it out into an
             array value,  returning  the  array  value.   (In  a
             scalar  context,  it  merely returns the first value
             produced.) The TEMPLATE has the same  format  as  in
             the  pack  function.   Here's a subroutine that does
             substring:

                  sub substr {
                       local($what,$where,$howmuch) = @_;
                       unpack("x$where a$howmuch", $what);
                  }

             and then there's

                  sub ord { unpack("c",$_[0]); }

             In addition, you may prefix a field with a %<number>
             to indicate that you want a <number>-bit checksum of
             the items instead of the items themselves.   Default
             is  a  16-bit  checksum.  For example, the following
             computes the same number as the System  V  sum  pro-
             gram:

                  while (<>) {
                      $checksum += unpack("%16C*", $_);
                  }
                  $checksum %= 65536;

     unshift(ARRAY,LIST)
             Does the opposite of a shift.  Or the opposite of  a
             push,  depending  on  how  you look at it.  Prepends
             list to the front of  the  array,  and  returns  the
             number of elements in the new array.

                  unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;

     utime(LIST)
     utime LIST
             Changes the access and modification  times  on  each
             file  of a list of files.  The first two elements of
             the list must be the NUMERICAL access and  modifica-
             tion  times,  in  that order.  Returns the number of
             files successfully changed.  The inode  modification
             time of each file is set to the current time.  Exam-
             ple of a "touch" command:

                  #!/usr/bin/perl
                  $now = time;
                  utime $now, $now, @ARGV;

     values(ASSOC_ARRAY)
     values ASSOC_ARRAY
             Returns a normal array consisting of all the  values
             of  the  named  associative  array.   The values are
             returned in an apparently random order,  but  it  is
             the  same order as either the keys() or each() func-
             tion would produce on  the  same  array.   See  also
             keys() and each().

     vec(EXPR,OFFSET,BITS)
             Treats a string as a vector  of  unsigned  integers,
             and  returns  the  value  of the bitfield specified.
             May also be assigned to.  BITS must be  a  power  of
             two from 1 to 32.

             Vectors created with vec() can also  be  manipulated
             with  the  logical  operators |, & and ^, which will
             assume a bit vector operation is desired  when  both
             operands  are  strings.   This interpretation is not
             enabled unless there is at least one vec()  in  your
             program, to protect older programs.

             To transform a bit vector into a string or array  of
             0's and 1's, use these:

                  $bits = unpack("b*", $vector);
                  @bits = split(//, unpack("b*", $vector));

             If you know the exact length in bits, it can be used
             in place of the *.

     wait    Waits for a child process to terminate  and  returns
             the  pid of the deceased process, or -1 if there are
             no child processes.  The status is returned in $?.

     waitpid(PID,FLAGS)
             Waits for a particular child  process  to  terminate
             and  returns  the pid of the deceased process, or -1
             if there is no such child process.   The  status  is
             returned in $?.  If you say

                  require "sys/wait.h";
                  ...
                  waitpid(-1,&WNOHANG);

             then you can do a non-blocking wait for any process.

             Non-blocking wait is only available on machines sup-
             porting either the waitpid (2) or wait4  (2)  system
             calls.   However,  waiting for a particular pid with
             FLAGS of 0 is implemented  everywhere.   (Perl  emu-
             lates  the  system  call  by  remembering the status
             values of processes that have exited  but  have  not
             been harvested by the Perl script yet.)

     wantarray
             Returns true if the context of the currently execut-
             ing  subroutine  is  looking  for  an  array  value.
             Returns false  if  the  context  is  looking  for  a
             scalar.

                  return wantarray ? () : undef;

     warn(LIST)
     warn LIST
             Produces a message on STDERR just  like  "die",  but
             doesn't exit.

     write(FILEHANDLE)
     write(EXPR)
     write   Writes a formatted record (possibly  multi-line)  to
             the specified file, using the format associated with
             that file.  By default the format for a file is  the
             one  having the same name is the filehandle, but the
             format for the current output channel  (see  select)
             may  be  set explicitly by assigning the name of the
             format to the $~ variable.

             Top of form processing is handled automatically:  if
             there  is  insufficient room on the current page for
             the formatted record, the page is advanced by  writ-
             ing  a  form  feed,  a special top-of-page format is
             used to format the new page  header,  and  then  the
             record  is written.  By default the top-of-page for-
             mat is  the  name  of  the  filehandle  with  "_TOP"
             appended, but it may be dynamicallly set to the for-
             mat of your choice by assigning the name to  the  $^
             variable  while  the  filehandle  is  selected.  The
             number of lines remaining on the current page is  in
             variable  $-,  which  can be set to 0 to force a new
             page.

             If FILEHANDLE is unspecified,  output  goes  to  the
             current  default output channel, which starts out as
             STDOUT but may be changed by  the  select  operator.

             If the FILEHANDLE is an EXPR, then the expression is
             evaluated and the resulting string is used  to  look
             up the name of the FILEHANDLE at run time.  For more
             on formats, see the section on Formats later on.

             Note that write is NOT the opposite of read.

==
     Precedence

     Perl operators have the  following  associativity  and  pre-
     cedence:

     nonassoc  print printf exec system sort reverse
                    chmod chown kill unlink utime die return
     left      ,
     right     = += -= *= etc.
     right     ?:
     nonassoc  ..
     left      ||
     left      &&
     left      | ^
     left      &
     nonassoc  == != <=> eq ne cmp
     nonassoc  < > <= >= lt gt le ge
     nonassoc  chdir exit eval reset sleep rand umask
     nonassoc  -r -w -x etc.
     left      << >>
     left      + - .
     left      * / % x
     left      =~ !~
     right     ! ~ and unary minus
     right     **
     nonassoc  ++ --
     left      '('

     As mentioned earlier, if any list operator (print, etc.)  or
     any  unary  operator  (chdir,  etc.)  is  followed by a left
     parenthesis as the next token on the same line, the operator
     and  arguments within parentheses are taken to be of highest
     precedence, just like a normal function call.  Examples:

          chdir $foo || die;       # (chdir $foo) || die
          chdir($foo) || die;      # (chdir $foo) || die
          chdir ($foo) || die;     # (chdir $foo) || die
          chdir +($foo) || die;    # (chdir $foo) || die

     but, because * is higher precedence than ||:

          chdir $foo * 20;         # chdir ($foo * 20)
          chdir($foo) * 20;        # (chdir $foo) * 20
          chdir ($foo) * 20;       # (chdir $foo) * 20
          chdir +($foo) * 20;      # chdir ($foo * 20)

          rand 10 * 20;            # rand (10 * 20)
          rand(10) * 20;           # (rand 10) * 20
          rand (10) * 20;          # (rand 10) * 20
          rand +(10) * 20;         # rand (10 * 20)

     In the absence of parentheses, the precedence of list opera-
     tors  such  as  print,  sort or chmod is either very high or
     very low depending on whether you look at the left  side  of
     operator or the right side of it.  For example, in

          @ary = (1, 3, sort 4, 2);
          print @ary;         # prints 1324

     the commas on the right of the sort are evaluated before the
     sort,  but  the  commas on the left are evaluated after.  In
     other words, list operators tend to gobble up all the  argu-
     ments that follow them, and then act like a simple term with
     regard to the preceding expression.  Note that you  have  to
     be careful with parens:

          # These evaluate exit before doing the print:
          print($foo, exit);  # Obviously not what you want.
          print $foo, exit;   # Nor is this.

          # These do the print before evaluating exit:
          (print $foo), exit; # This is what you want.
          print($foo), exit;  # Or this.
          print ($foo), exit; # Or even this.

     Also note that

          print ($foo & 255) + 1, "\n";

     probably doesn't do what you expect at first glance.

     Subroutines

     A subroutine may be declared as follows:

         sub NAME BLOCK

     Any arguments passed to the routine come  in  as  array  @_,
     that is ($_[0], $_[1], ...).  The array @_ is a local array,
     but its values are references to the actual  scalar  parame-
     ters.   The  return  value of the subroutine is the value of
     the last expression evaluated, and can be  either  an  array
     value  or  a  scalar value.  Alternately, a return statement
     may be used to specify the returned value and exit the  sub-
     routine.  To create local variables see the local operator.

     A subroutine is called using the do operator or the & opera-
     tor.

     Example:

          sub MAX {
               local($max) = pop(@_);
               foreach $foo (@_) {
                    $max = $foo if $max < $foo;
               }
               $max;
          }

          ...
          $bestday = &MAX($mon,$tue,$wed,$thu,$fri);

     Example:

          # get a line, combining continuation lines
          #  that start with whitespace
          sub get_line {
               $thisline = $lookahead;
               line: while ($lookahead = <STDIN>) {
                    if ($lookahead =~ /^[ \t]/) {
                         $thisline .= $lookahead;
                    }
                    else {
                         last line;
                    }
               }
               $thisline;
          }

          $lookahead = <STDIN>;    # get first line
          while ($_ = do get_line()) {
               ...
          }

     Use array assignment to a local list to name your formal arguments:

          sub maybeset {
               local($key, $value) = @_;
               $foo{$key} = $value unless $foo{$key};
          }

     This also has the effect of turning  call-by-reference  into
     call-by-value, since the assignment copies the values.

     Subroutines may be called recursively.  If a  subroutine  is
     called  using the & form, the argument list is optional.  If
     omitted, no @_ array is set up for the  subroutine;  the  @_
     array  at  the  time  of  the  call is visible to subroutine
     instead.

          do foo(1,2,3);      # pass three arguments
          &foo(1,2,3);        # the same

          do foo();      # pass a null list
          &foo();             # the same
          &foo;               # pass no arguments--more efficient

     Passing By Reference

     Sometimes you don't want to pass the value of an array to  a
     subroutine but rather the name of it, so that the subroutine
     can modify the global copy of it rather than working with  a
     local  copy.   In perl you can refer to all the objects of a
     particular name by prefixing the name  with  a  star:  *foo.
     When  evaluated,  it produces a scalar value that represents
     all the objects of that name, including any filehandle, for-
     mat or subroutine.  When assigned to within a local() opera-
     tion, it causes the name mentioned to refer  to  whatever  *
     value was assigned to it.  Example:

          sub doubleary {
              local(*someary) = @_;
              foreach $elem (@someary) {
               $elem *= 2;
              }
          }
          do doubleary(*foo);
          do doubleary(*bar);

     Assignment to *name is currently recommended only  inside  a
     local().  You can actually assign to *name anywhere, but the
     previous referent of *name may be  stranded  forever.   This
     may or may not bother you.

     Note that scalars are already passed by  reference,  so  you
     can  modify scalar arguments without using this mechanism by
     referring explicitly to the $_[nnn] in  question.   You  can
     modify  all the elements of an array by passing all the ele-
     ments as scalars, but you have to use  the  *  mechanism  to
     push,  pop  or change the size of an array.  The * mechanism
     will probably be more efficient in any case.

     Since a *name value contains unprintable binary data, if  it
     is  used as an argument in a print, or as a %s argument in a
     printf or sprintf, it then has the value '*name', just so it
     prints out pretty.

     Even if you don't want to modify an array, this mechanism is
     useful  for  passing multiple arrays in a single LIST, since
     normally the LIST mechanism will merge all the array  values
     so that you can't extract out the individual arrays.

     Regular Expressions

     The patterns used in pattern matching  are  regular  expres-
     sions  such  as  those supplied in the Version 8 regexp rou-
     tines.  (In  fact,  the  routines  are  derived  from  Henry
     Spencer's  freely redistributable reimplementation of the V8
     routines.) In addition, \w matches an alphanumeric character
     (including  "_")  and \W a nonalphanumeric.  Word boundaries
     may be matched by \b, and  non-boundaries  by  \B.   A  whi-
     tespace character is matched by \s, non-whitespace by \S.  A
     numeric character is matched by \d, non-numeric by \D.   You
     may  use  \w, \s and \d within character classes.  Also, \n,
     \r, \f, \t  and  \NNN  have  their  normal  interpretations.
     Within character classes \b represents backspace rather than
     a word boundary.  Alternatives may be separated by  |.   The
     bracketing construct ( ... ) may also be used, in which case
     \<digit> matches the digit'th substring.   (Outside  of  the
     pattern,  always  use  $ instead of \ in front of the digit.
     The scope of $<digit> (and $`, $& and $') extends to the end
     of  the  enclosing BLOCK or eval string, or to the next pat-
     tern match with subexpressions.  The \<digit> notation some-
     times  works  outside the current pattern, but should not be
     relied upon.) You may have as many parentheses as you  wish.
     If  you have more than 9 substrings, the variables $10, $11,
     ... refer to the corresponding substring.  Within  the  pat-
     tern,  \10, \11, etc. refer back to substrings if there have
     been at least that many left parens  before  the  backrefer-
     ence.  Otherwise (for backward compatibilty) \10 is the same
     as \010, a backspace, and \11 the same as \011, a tab.   And
     so on.  (\1 through \9 are always backreferences.)

     $+ returns whatever the  last  bracket  match  matched.   $&
     returns  the  entire matched string.  ($0 used to return the
     same thing, but not any more.) $` returns everything  before
     the matched string.  $' returns everything after the matched
     string.  Examples:

          s/^([^ ]*) *([^ ]*)/$2 $1/;   # swap first two words

          if (/Time: (..):(..):(..)/) {
               $hours = $1;
               $minutes = $2;
               $seconds = $3;
          }

     By default, the ^ character is only guaranteed to  match  at
     the beginning of the string, the $ character only at the end
     (or before the newline at the end)  and  perl  does  certain
     optimizations  with  the assumption that the string contains
     only one line.  The behavior of ^ and $ on embedded newlines
     will  be  inconsistent.   You  may, however, wish to treat a
     string as a multi-line buffer, such that the  ^  will  match
     after any newline within the string, and $ will match before
     any newline.  At the cost of a little more overhead, you can
     do this by setting the variable $* to 1.  Setting it back to
     0 makes perl revert to its old behavior.

     To facilitate  multi-line  substitutions,  the  .  character
     never matches a newline (even when $* is 0).  In particular,
     the following leaves a newline on the $_ string:

          $_ = <STDIN>;
          s/.*(some_string).*/$1/;

     If the newline is unwanted, try one of

          s/.*(some_string).*\n/$1/;
          s/.*(some_string)[^\000]*/$1/;
          s/.*(some_string)(.|\n)*/$1/;
          chop; s/.*(some_string).*/$1/;
          /(some_string)/ && ($_ = $1);

     Any item of a regular expression may be followed with digits
     in  curly  brackets  of  the  form  {n,m}, where n gives the
     minimum number of times to match the item and  m  gives  the
     maximum.   The  form  {n} is equivalent to {n,n} and matches
     exactly n times.  The form {n,} matches  n  or  more  times.
     (If  a  curly  bracket  occurs  in  any other context, it is
     treated  as  a  regular  character.)  The  *   modifier   is
     equivalent  to {0,}, the + modifier to {1,} and the ? modif-
     ier to {0,1}.  There is no limit to the size of n or m,  but
     large numbers will chew up more memory.

     You will note that all backslashed  metacharacters  in  perl
     are  alphanumeric,  such  as  \b, \w, \n.  Unlike some other
     regular expression languages, there are no backslashed  sym-
     bols  that aren't alphanumeric.  So anything that looks like
     \\, \(, \), \<, \>, \{, or \} is  always  interpreted  as  a
     literal  character, not a metacharacter.  This makes it sim-
     ple to quote a string that you want to use for a pattern but
     that  you  are  afraid might contain metacharacters.  Simply
     quote all the non-alphanumeric characters:

          $pattern =~ s/(\W)/\\$1/g;

     Formats

     Output record formats for use with the  write  operator  may
     declared as follows:

         format NAME =
         FORMLIST
         .

     If name is omitted, format "STDOUT"  is  defined.   FORMLIST
     consists of a sequence of lines, each of which may be of one
     of three types:

     1.  A comment.

     2.  A "picture" line giving the format for one output line.

     3.  An argument line supplying values to plug into a picture
         line.

     Picture lines are printed exactly as they look,  except  for
     certain  fields  that substitute values into the line.  Each
     picture field starts with either @ or ^.  The @  field  (not
     to  be confused with the array marker @) is the normal case;
     ^ fields are used to do rudimentary  multi-line  text  block
     filling.  The length of the field is supplied by padding out
     the field with multiple <, >, or |  characters  to  specify,
     respectively,  left  justification,  right justification, or
     centering.  As an alternate form of right justification, you
     may  also use # characters (with an optional .) to specify a
     numeric field.  (Use of ^ instead of @ causes the  field  to
     be  blanked if undefined.) If any of the values supplied for
     these fields contains a newline, only the  text  up  to  the
     newline  is  printed.   The special field @* can be used for
     printing multi-line values.  It should appear by itself on a
     line.

     The values are specified on the following line, in the  same
     order as the picture fields.  The values should be separated
     by commas.

     Picture fields that begin with ^ rather than @  are  treated
     specially.   The  value  supplied  must be a scalar variable
     name which contains a text string.  Perl puts as  much  text
     as  it  can  into the field, and then chops off the front of
     the string so that the next time the variable is referenced,
     more  of  the text can be printed.  Normally you would use a
     sequence of fields in a vertical stack to print out a  block
     of text.  If you like, you can end the final field with ...,
     which will appear in the output if the text was too long  to
     appear in its entirety.  You can change which characters are
     legal to break on by changing the variable $: to a  list  of
     the desired characters.

     Since use of ^ fields can produce variable length records if
     the  text  to  be formatted is short, you can suppress blank
     lines by putting the tilde (~)  character  anywhere  in  the
     line.  (Normally you should put it in the front if possible,
     for visibility.) The tilde will be  translated  to  a  space
     upon  output.   If  you put a second tilde contiguous to the
     first, the line will be repeated until all the fields on the
     line  are  exhausted.  (If you use a field of the @ variety,
     the expression you supply had better not give the same value
     every time forever!)

     Examples:

     # a report on the /etc/passwd file
     format STDOUT_TOP =
                             Passwd File
     Name                Login    Office   Uid   Gid Home
     ------------------------------------------------------------------
     .
     format STDOUT =
     @<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
     $name,              $login,  $office,$uid,$gid, $home
     .

     # a report from a bug report form
     format STDOUT_TOP =
                             Bug Reports
     @<<<<<<<<<<<<<<<<<<<<<<<     @|||         @>>>>>>>>>>>>>>>>>>>>>>>
     $system,                      $%,         $date
     ------------------------------------------------------------------
     .
     format STDOUT =
     Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
              $subject
     Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
            $index,                       $description
     Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
               $priority,        $date,   $description
     From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
           $from,                         $description
     Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                  $programmer,            $description
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                          $description
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                          $description
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                          $description
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                          $description
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<...
                                          $description
     .

     It is possible to intermix prints with writes  on  the  same
     output  channel, but you'll have to handle $- (lines left on
     the page) yourself.

     If you are printing lots of fields that are  usually  blank,
     you   should  consider  using  the  reset  operator  between
     records.  Not only is it more efficient, but it can  prevent
     the bug of adding another field and forgetting to zero it.

     Interprocess Communication

     The IPC facilities of perl are built on the Berkeley  socket
     mechanism.   If  you don't have sockets, you can ignore this
     section.  The calls have the same names as the corresponding
     system calls, but the arguments tend to differ, for two rea-
     sons.  First, perl file handles work differently than C file
     descriptors.   Second,  perl already knows the length of its
     strings, so you don't need to pass that  information.   Here
     is a sample client (untested):

          ($them,$port) = @ARGV;
          $port = 2345 unless $port;
          $them = 'localhost' unless $them;

          $SIG{'INT'} = 'dokill';
          sub dokill { kill 9,$child if $child; }

          require 'sys/socket.ph';

          $sockaddr = 'S n a4 x8';
          chop($hostname = `hostname`);

          ($name, $aliases, $proto) = getprotobyname('tcp');
          ($name, $aliases, $port) = getservbyname($port, 'tcp')
               unless $port =~ /^\d+$/;
          ($name, $aliases, $type, $len, $thisaddr) =
                              gethostbyname($hostname);
          ($name, $aliases, $type, $len, $thataddr) = gethostbyname($them);

          $this = pack($sockaddr, &AF_INET, 0, $thisaddr);
          $that = pack($sockaddr, &AF_INET, $port, $thataddr);

          socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
          bind(S, $this) || die "bind: $!";
          connect(S, $that) || die "connect: $!";

          select(S); $| = 1; select(stdout);

          if ($child = fork) {
               while (<>) {
                    print S;
               }
               sleep 3;

               do dokill();
          }
          else {
               while (<S>) {
                    print;
               }
          }

     And here's a server:

          ($port) = @ARGV;
          $port = 2345 unless $port;

          require 'sys/socket.ph';

          $sockaddr = 'S n a4 x8';

          ($name, $aliases, $proto) = getprotobyname('tcp');
          ($name, $aliases, $port) = getservbyname($port, 'tcp')
               unless $port =~ /^\d+$/;

          $this = pack($sockaddr, &AF_INET, $port, "\0\0\0\0");

          select(NS); $| = 1; select(stdout);

          socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
          bind(S, $this) || die "bind: $!";
          listen(S, 5) || die "connect: $!";

          select(S); $| = 1; select(stdout);

          for (;;) {
               print "Listening again\n";
               ($addr = accept(NS,S)) || die $!;
               print "accept ok\n";

               ($af,$port,$inetaddr) = unpack($sockaddr,$addr);
               @inetaddr = unpack('C4',$inetaddr);
               print "$af $port @inetaddr\n";

               while (<NS>) {
                    print;
                    print NS;
               }
          }

     Predefined Names

     The following names have special meaning to perl.   I  could
     have used alphabetic symbols for some of these, but I didn't
     want to  take  the  chance  that  someone  would  say  reset
     "a-zA-Z"  and wipe them all out.  You'll just have to suffer
     along with these silly symbols.  Most of them  have  reason-
     able mnemonics, or analogues in one of the shells.

     $_      The default input and pattern-searching space.   The
             following pairs are equivalent:

                  while (<>) {...     # only equivalent in while!
                  while ($_ = <>) {...

                  /^Subject:/
                  $_ =~ /^Subject:/

                  y/a-z/A-Z/
                  $_ =~ y/a-z/A-Z/

                  chop
                  chop($_)

             (Mnemonic: underline is understood in certain opera-
             tions.)

     $.      The current input line number of the last filehandle
             that  was  read.   Readonly.   Remember that only an
             explicit close on the  filehandle  resets  the  line
             number.  Since <> never does an explicit close, line
             numbers increase across ARGV files (but see examples
             under  eof).  (Mnemonic: many programs use . to mean
             the current line number.)

     $/      The input  record  separator,  newline  by  default.
             Works  like  awk's  RS  variable, including treating
             blank lines as delimiters if set to the null string.
             You may set it to a multicharacter string to match a
             multi-character delimiter.  (Mnemonic: / is used  to
             delimit line boundaries when quoting poetry.)

     $,      The output field separator for the  print  operator.
             Ordinarily  the print operator simply prints out the
             comma separated fields you specify.  In order to get
             behavior  more  like  awk,  set this variable as you
             would set awk's OFS  variable  to  specify  what  is
             printed  between fields.  (Mnemonic: what is printed
             when there is a , in your print statement.)

     $"      This is like $, except  that  it  applies  to  array
             values  interpolated into a double-quoted string (or
             similar interpreted string).  Default  is  a  space.
             (Mnemonic: obvious, I think.)

     $\      The output record separator for the print  operator.
             Ordinarily  the print operator simply prints out the
             comma separated fields you specify, with no trailing
             newline  or  record  separator assumed.  In order to
             get behavior more like awk, set this variable as you
             would  set  awk's  ORS  variable  to specify what is
             printed at the end of the print.  (Mnemonic: you set
             $\  instead  of  adding  \n at the end of the print.
             Also, it's just like /, but it's what you get "back"
             from perl.)

     $#      The output format for printed numbers.   This  vari-
             able is a half-hearted attempt to emulate awk's OFMT
             variable.  There are times, however,  when  awk  and
             perl  have  differing  notions  of  what  is in fact
             numeric.  Also, the initial value  is  %.20g  rather
             than  %.6g,  so you need to set $# explicitly to get
             awk's value.  (Mnemonic: # is the number sign.)

     $%      The current page number of  the  currently  selected
             output  channel.   (Mnemonic:  %  is  page number in
             nroff.)

     $=      The current page length  (printable  lines)  of  the
             currently  selected  output channel.  Default is 60.
             (Mnemonic: = has horizontal lines.)

     $-      The  number  of  lines  left  on  the  page  of  the
             currently   selected   output  channel.   (Mnemonic:
             lines_on_page - lines_printed.)

     $~      The name  of  the  current  report  format  for  the
             currently  selected output channel.  Default is name
             of the filehandle.  (Mnemonic: brother to $^.)

     $^      The name of the current top-of-page format  for  the
             currently  selected output channel.  Default is name
             of the filehandle with "_TOP" appended.   (Mnemonic:
             points to top of page.)

     $|      If set to nonzero, forces a flush after every  write
             or  print  on the currently selected output channel.
             Default is 0.  Note that STDOUT  will  typically  be
             line buffered if output is to the terminal and block
             buffered otherwise.  Setting this variable is useful
             primarily when you are outputting to a pipe, such as
             when you are running a perl  script  under  rsh  and
             want   to   see   the   output  as  it's  happening.
             (Mnemonic: when you want your  pipes  to  be  piping
             hot.)

     $$      The process number of the perl running this  script.
             (Mnemonic: same as shells.)

     $?      The status returned by the last pipe close, backtick
             (``)  command or system operator.  Note that this is
             the status word returned by the wait() system  call,
             so  the exit value of the subprocess is actually ($?
             >> 8).  $? & 255 gives which  signal,  if  any,  the
             process  died  from,  and  whether  there was a core
             dump.  (Mnemonic: similar to sh and ksh.)

     $&      The string matched by the last  pattern  match  (not
             counting  any  matches hidden within a BLOCK or eval
             enclosed by the current BLOCK).  (Mnemonic:  like  &
             in some editors.)

     $`      The string preceding whatever  was  matched  by  the
             last  pattern match (not counting any matches hidden
             within a BLOCK  or  eval  enclosed  by  the  current
             BLOCK).    (Mnemonic:  `  often  precedes  a  quoted
             string.)

     $'      The string following whatever  was  matched  by  the
             last  pattern match (not counting any matches hidden
             within a BLOCK  or  eval  enclosed  by  the  current
             BLOCK).    (Mnemonic:   '  often  follows  a  quoted
             string.) Example:

                  $_ = 'abcdefghi';
                  /def/;
                  print "$`:$&:$'\n";      # prints abc:def:ghi

     $+      The last bracket matched by the last search pattern.
             This  is  useful if you don't know which of a set of
             alternative patterns matched.  For example:

                 /Version: (.*)|Revision: (.*)/ && ($rev = $+);

             (Mnemonic: be positive and forward looking.)

     $*      Set to 1 to do multiline matching within a string, 0
             to tell perl that it can assume that strings contain
             a single line, for the purpose of optimizing pattern
             matches.  Pattern matches on strings containing mul-
             tiple newlines can produce confusing results when $*
             is  0.  Default is 0.  (Mnemonic: * matches multiple
             things.) Note that this variable only influences the
             interpretation of ^ and $.  A literal newline can be
             searched for even when $* == 0.

     $0      Contains the name of the file  containing  the  perl
             script being executed.  Assigning to $0 modifies the
             argument  area  that   the   ps(1)   program   sees.
             (Mnemonic: same as sh and ksh.)

     $<digit>
             Contains the subpattern from the  corresponding  set
             of  parentheses  in  the  last  pattern matched, not
             counting patterns matched in nested blocks that have
             been exited already.  (Mnemonic: like \digit.)

     $[      The index of the first element in an array,  and  of
             the  first  character in a substring.  Default is 0,
             but you could set it to 1 to make perl  behave  more
             like  awk  (or  Fortran)  when subscripting and when
             evaluating  the  index()  and  substr()   functions.
             (Mnemonic: [ begins subscripts.)

     $]      The string printed out when you say "perl  -v".   It
             can  be  used  to  determine  at  the beginning of a
             script whether the perl  interpreter  executing  the
             script  is  in the right range of versions.  If used
             in  a  numeric  context,  returns  the   version   +
             patchlevel / 1000.  Example:

                  # see if getc is available
                     ($version,$patchlevel) =
                        $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;
                     print STDERR "(No filename completion available.)\n"
                        if $version * 1000 + $patchlevel < 2016;

             or, used numerically,

                  warn "No checksumming!\n" if $] < 3.019;

             (Mnemonic: Is this version  of  perl  in  the  right
             bracket?)

     $;      The subscript separator for multi-dimensional  array
             emulation.   If  you  refer  to an associative array
             element as
                  $foo{$a,$b,$c}

             it really means

                  $foo{join($;, $a, $b, $c)}

             But don't put

                  @foo{$a,$b,$c}      # a slice--note the @

             which means

                  ($foo{$a},$foo{$b},$foo{$c})

             Default is "\034", the same as SUBSEP in awk.   Note
             that  if  your  keys contain binary data there might
             not be any safe value for $;.  (Mnemonic: comma (the
             syntactic  subscript separator) is a semi-semicolon.
             Yeah, I know, it's pretty lame, but  $,  is  already
             taken for something more important.)

     $!      If used in a numeric  context,  yields  the  current
             value  of  errno, with all the usual caveats.  (This
             means that you shouldn't depend on the value  of  $!
             to  be anything in particular unless you've gotten a
             specific error return indicating a system error.) If
             used  in  a string context, yields the corresponding
             system error string.  You can assign to $! in  order
             to set errno if, for instance, you want $! to return
             the string for error n, or you want to set the  exit
             value  for  the  die operator.  (Mnemonic: What just
             went bang?)

     $@      The perl syntax error message  from  the  last  eval
             command.  If null, the last eval parsed and executed
             correctly (although the operations you  invoked  may
             have  failed  in  the  normal  fashion).  (Mnemonic:
             Where was the syntax error "at"?)

     $<      The real uid of this process.  (Mnemonic:  it's  the
             uid you came FROM, if you're running setuid.)

     $>      The effective uid of this process.  Example:

                  $< = $>;  # set real uid to the effective uid
                  ($<,$>) = ($>,$<);  # swap real and effective uid

             (Mnemonic: it's the uid you went TO, if you're  run-
             ning setuid.) Note: $< and $> can only be swapped on
             machines supporting setreuid().

     $(      The real gid of this  process.   If  you  are  on  a
             machine  that supports membership in multiple groups
             simultaneously, gives  a  space  separated  list  of
             groups  you  are  in.   The  first number is the one
             returned by getgid(), and  the  subsequent  ones  by
             getgroups(),  one  of  which  may be the same as the
             first number.  (Mnemonic: parentheses  are  used  to
             GROUP  things.   The real gid is the group you LEFT,
             if you're running setgid.)

     $)      The effective gid of this process.  If you are on  a
             machine  that supports membership in multiple groups
             simultaneously, gives  a  space  separated  list  of
             groups  you  are  in.   The  first number is the one
             returned by getegid(), and the  subsequent  ones  by
             getgroups(),  one  of  which  may be the same as the
             first number.  (Mnemonic: parentheses  are  used  to
             GROUP things.  The effective gid is the group that's
             RIGHT for you, if you're running setgid.)

             Note: $<, $>, $( and $) can only be set on  machines
             that  support the corresponding set[re][ug]id() rou-
             tine.  $( and $) can only  be  swapped  on  machines
             supporting setregid().

     $:      The current set of characters after which  a  string
             may  be broken to fill continuation fields (starting
             with ^) in a format.  Default is " \n-", to break on
             whitespace or hyphens.  (Mnemonic: a "colon" in poe-
             try is a part of a line.)

     $^D     The  current   value   of   the   debugging   flags.
             (Mnemonic: value of -D switch.)

     $^F     The maximum system file  descriptor,  ordinarily  2.
             System  file descriptors are passed to subprocesses,
             while higher file descriptors are  not.   During  an
             open,  system file descriptors are preserved even if
             the  open  fails.   Ordinary  file  descriptors  are
             closed before the open is attempted.

     $^I     The current value  of  the  inplace-edit  extension.
             Use  undef  to  disable inplace editing.  (Mnemonic:
             value of -i switch.)

     $^P     The internal flag that the debugger clears  so  that
             it doesn't debug itself.  You could conceivable dis-
             able debugging yourself by clearing it.

     $^T     The time at  which  the  script  began  running,  in
             seconds since the epoch.  The values returned by the
             -M , -A and -C filetests are based on this value.

     $^W     The current value of the warning switch.  (Mnemonic:
             related to the -w switch.)

     $^X     The name that Perl  itself  was  executed  as,  from
             argv[0].

     $ARGV   contains the name of the current file  when  reading
             from <>.

     @ARGV   The array ARGV contains the command  line  arguments
             intended  for  the  script.  Note that $#ARGV is the
             generally  number  of  arguments  minus  one,  since
             $ARGV[0]  is  the  first  argument,  NOT the command
             name.  See $0 for the command name.

     @INC    The array INC contains the list of  places  to  look
             for  perl  scripts  to be evaluated by the "do EXPR"
             command or the "require" command.  It initially con-
             sists  of  the  arguments  to  any  -I  command line
             switches, followed  by  the  default  perl  library,
             probably  "/usr/local/lib/perl", followed by ".", to
             represent the current directory.

     %INC    The associative array INC contains entries for  each
             filename   that   has  been  included  via  "do"  or
             "require".  The key is the filename  you  specified,
             and  the  value is the location of the file actually
             found.  The "require" command  uses  this  array  to
             determine  whether  a  given  file  has already been
             included.

     $ENV{expr}
             The associative  array  ENV  contains  your  current
             environment.   Setting  a  value  in ENV changes the
             environment for child processes.

     $SIG{expr}
             The associative array SIG  is  used  to  set  signal
             handlers for various signals.  Example:

                  sub handler {  # 1st argument is signal name
                       local($sig) = @_;
                       print "Caught a SIG$sig--shutting down\n";
                       close(LOG);
                       exit(0);
                  }

                  $SIG{'INT'} = 'handler';
                  $SIG{'QUIT'} = 'handler';
                  ...
                  $SIG{'INT'} = 'DEFAULT'; # restore default action
                  $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT

             The SIG array only contains values for  the  signals
             actually set within the perl script.

     Packages

     Perl provides a mechanism for alternate namespaces  to  pro-
     tect  packages  from  stomping on each others variables.  By
     default, a perl script starts  compiling  into  the  package
     known as "main".  By use of the package declaration, you can
     switch namespaces.  The scope of the package declaration  is
     from  the  declaration  itself  to  the end of the enclosing
     block (the same scope as the local()  operator).   Typically
     it  would  be the first declaration in a file to be included
     by the "require" operator.  You can switch into a package in
     more than one place; it merely influences which symbol table
     is used by the compiler for the rest of that block.  You can
     refer to variables and filehandles in other packages by pre-
     fixing the identifier with the package  name  and  a  single
     quote.   If  the package name is null, the "main" package as
     assumed.

     Only identifiers starting with letters  are  stored  in  the
     packages  symbol table.  All other symbols are kept in pack-
     age "main".  In addition,  the  identifiers  STDIN,  STDOUT,
     STDERR,  ARGV, ARGVOUT, ENV, INC and SIG are forced to be in
     package "main", even when used for other purposes than their
     built-in  one.  Note also that, if you have a package called
     "m", "s" or "y", the you can't use the qualified form of  an
     identifier since it will be interpreted instead as a pattern
     match, a substitution or a translation.

     Eval'ed strings are compiled in the  package  in  which  the
     eval  was  compiled  in.   (Assignments  to $SIG{}, however,
     assume the signal handler specified is in the main  package.
     Qualify the signal handler name if you wish to have a signal
     handler in a package.) For an example, examine perldb.pl  in
     the  perl  library.  It initially switches to the DB package
     so that the debugger doesn't interfere with variables in the
     script you are trying to debug.  At various points, however,
     it temporarily switches back to the main package to evaluate
     various expressions in the context of the main package.

     The symbol table for a package happens to be stored  in  the
     associative array of that name prepended with an underscore.
     The value in each entry of the associative array is what you
     are  referring to when you use the *name notation.  In fact,
     the following have the same effect (in  package  main,  any-
     way), though the first is more efficient because it does the
     symbol table lookups at compile time:

          local(*foo) = *bar;
          local($_main{'foo'}) = $_main{'bar'};

     You can use this to print out all the variables in  a  pack-
     age,  for  instance.   Here  is  dumpvar.pl  from  the  perl
     library:

          package dumpvar;

          sub main'dumpvar {
              ($package) = @_;
              local(*stab) = eval("*_$package");
              while (($key,$val) = each(%stab)) {
                  {
                      local(*entry) = $val;
                      if (defined $entry) {
                          print "\$$key = '$entry'\n";
                      }
                      if (defined @entry) {
                          print "\@$key = (\n";
                          foreach $num ($[ .. $#entry) {
                              print "  $num\t'",$entry[$num],"'\n";
                          }
                          print ")\n";
                      }
                      if ($key ne "_$package" && defined %entry) {
                          print "\%$key = (\n";
                          foreach $key (sort keys(%entry)) {
                              print "  $key\t'",$entry{$key},"'\n";
                          }
                          print ")\n";
                      }
                  }
              }
          }

     Note that, even though the subroutine is compiled in package
     dumpvar, the name of the subroutine is qualified so that its
     name is inserted into package "main".

     Style

     Each programmer will, of course, have his or her own prefer-
     ences  in  regards to formatting, but there are some general
     guidelines that will make your programs easier to read.

     1.  Just because you  CAN  do  something  a  particular  way
         doesn't  mean  that  you SHOULD do it that way.  Perl is
         designed to give you several ways  to  do  anything,  so
         consider picking the most readable one.  For instance

              open(FOO,$foo) || die "Can't open $foo: $!";

         is better than

              die "Can't open $foo: $!" unless open(FOO,$foo);

         because the second way  hides  the  main  point  of  the
         statement in a modifier.  On the other hand

              print "Starting analysis\n" if $verbose;

         is better than

              $verbose && print "Starting analysis\n";

         since the main point isn't whether the user typed -v  or
         not.

         Similarly, just because  an  operator  lets  you  assume
         default arguments doesn't mean that you have to make use
         of the defaults.  The defaults are there for  lazy  sys-
         tems programmers writing one-shot programs.  If you want
         your program to  be  readable,  consider  supplying  the
         argument.

         Along  the  same  lines,  just  because  you  can   omit
         parentheses  in  many places doesn't mean that you ought
         to:

              return print reverse sort num values array;
              return print(reverse(sort num (values(%array))));

         When in doubt, parenthesize.  At the very least it  will
         let some poor schmuck bounce on the % key in vi.

         Even if you aren't in doubt, consider the mental welfare
         of  the  person  who has to maintain the code after you,
         and who will probably put parens in the wrong place.

     2.  Don't go through silly contortions to exit a loop at the
         top  or the bottom, when perl provides the "last" opera-
         tor so you can exit in the middle.  Just  outdent  it  a
         little to make it more visible:

             line:
              for (;;) {
                  statements;
              last line if $foo;
                  next line if /^#/;
                  statements;
              }

     3.  Don't be afraid to use  loop  labels--they're  there  to
         enhance readability as well as to allow multi-level loop
         breaks.  See last example.

     4.  For portability, when using features  that  may  not  be
         implemented  on  every machine, test the construct in an
         eval to see if it fails.  If you know  what  version  or
         patchlevel a particular feature was implemented, you can
         test $] to see if it will be there.

     5.  Choose mnemonic identifiers.

     6.  Be consistent.

     Debugging

     If you invoke perl with a -d switch, your script will be run
     under  a  debugging  monitor.  It will halt before the first
     executable statement and ask you for a command, such as:

     h           Prints out a help message.

     T           Stack trace.

     s           Single step.   Executes  until  it  reaches  the
                 beginning of another statement.

     n           Next.  Executes over subroutine calls, until  it
                 reaches the beginning of the next statement.

     f           Finish.  Executes statements until it  has  fin-
                 ished the current subroutine.

     c           Continue.  Executes until the next breakpoint is
                 reached.

     c line      Continue to the specified line.  Inserts a  one-
                 time-only breakpoint at the specified line.

     <CR>        Repeat last n or s.

     l min+incr  List incr+1 lines starting at min.   If  min  is
                 omitted, starts where last listing left off.  If
                 incr is omitted, previous value of incr is used.

     l min-max   List lines in the indicated range.

     l line      List just the indicated line.

     l           List next window.

     -           List previous window.

     w line      List window around line.

     l subname   List subroutine.  If it's a long  subroutine  it
                 just lists the beginning.  Use "l" to list more.

     /pattern/   Regular expression search forward  for  pattern;
                 the final / is optional.

     ?pattern?   Regular expression search backward for  pattern;
                 the final ? is optional.

     L           List lines that have breakpoints or actions.

     S           Lists the names of all subroutines.

     t           Toggle trace mode on or off.

     b line condition
                 Set a breakpoint.  If line is  omitted,  sets  a
                 breakpoint  on the line that is about to be exe-
                 cuted.  If  a  condition  is  specified,  it  is
                 evaluated each time the statement is reached and
                 a breakpoint is taken only if the  condition  is
                 true.  Breakpoints may only be set on lines that
                 begin an executable statement.

     b subname condition
                 Set breakpoint at first executable line of  sub-
                 routine.

     d line      Delete breakpoint.  If line is omitted,  deletes
                 the  breakpoint  on the line that is about to be
                 executed.

     D           Delete all breakpoints.

     a line command
                 Set an action for line.   A  multi-line  command
                 may be entered by backslashing the newlines.

     A           Delete all line actions.

     < command   Set an action to happen  before  every  debugger
                 prompt.   A multi-line command may be entered by
                 backslashing the newlines.

     > command   Set an action to happen after  the  prompt  when
                 you've just given a command to return to execut-
                 ing the script.  A  multi-line  command  may  be
                 entered by backslashing the newlines.

     V package   List all variables in package.  Default is  main
                 package.

     ! number    Redo a debugging command.  If number is omitted,
                 redoes the previous command.

     ! -number   Redo the command that  was  that  many  commands
                 ago.

     H -number   Display last n commands.  Only  commands  longer
                 than  one  character  are  listed.  If number is
                 omitted, lists them all.

     q or ^D     Quit.

     command     Execute command as a perl statement.  A  missing
                 semicolon will be supplied.

     p expr      Same  as  "print  DB'OUT  expr".    The   DB'OUT
                 filehandle  is opened to /dev/tty, regardless of
                 where STDOUT may be redirected to.

     If you want to modify the debugger, copy perldb.pl from  the
     perl  library  to  your  current  directory and modify it as
     necessary.  (You'll also have to put  -I.  on  your  command
     line.) You can do some customization by setting up a .perldb
     file which contains initialization code.  For instance,  you
     could make aliases like these:

         $DB'alias{'len'} = 's/^len(.*)/p length($1)/';
         $DB'alias{'stop'} = 's/^stop (at|in)/b/';
         $DB'alias{'.'} =
           's/^\./p "\$DB\'sub(\$DB\'line):\t",\$DB\'line[\$DB\'line]/';

     Setuid Scripts

     Perl is designed to make it easy to write secure setuid  and
     setgid  scripts.  Unlike shells, which are based on multiple
     substitution passes on each line of the script, perl uses  a
     more   conventional  evaluation  scheme  with  fewer  hidden
     "gotchas".   Additionally,  since  the  language  has   more
     built-in  functionality,  it  has to rely less upon external
     (and possibly untrustworthy) programs to accomplish its pur-
     poses.

     In an unpatched 4.2 or 4.3bsd  kernel,  setuid  scripts  are
     intrinsically  insecure, but this kernel feature can be dis-
     abled.  If it is, perl can emulate  the  setuid  and  setgid
     mechanism  when  it notices the otherwise useless setuid/gid
     bits on perl scripts.  If the kernel feature isn't disabled,
     perl  will  complain  loudly  that  your  setuid  script  is
     insecure.  You'll need to either disable the  kernel  setuid
     script feature, or put a C wrapper around the script.

     When perl is executing a setuid  script,  it  takes  special
     precautions  to  prevent  you  from falling into any obvious
     traps.  (In some ways, a perl script is more secure than the
     corresponding   C   program.)  Any  command  line  argument,
     environment variable, or input is marked as  "tainted",  and
     may not be used, directly or indirectly, in any command that
     invokes a subshell, or in any command that  modifies  files,
     directories  or  processes.  Any variable that is set within
     an expression that has previously referenced a tainted value
     also becomes tainted (even if it is logically impossible for
     the tainted value to influence the variable).  For example:

          $foo = shift;            # $foo is tainted
          $bar = $foo,'bar';       # $bar is also tainted
          $xxx = <>;               # Tainted
          $path = $ENV{'PATH'};    # Tainted, but see below
          $abc = 'abc';            # Not tainted

          system "echo $foo";      # Insecure
          system "/bin/echo", $foo;     # Secure (doesn't use sh)
          system "echo $bar";      # Insecure
          system "echo $abc";      # Insecure until PATH set

          $ENV{'PATH'} = '/bin:/usr/bin';
          $ENV{'IFS'} = '' if $ENV{'IFS'} ne '';

          $path = $ENV{'PATH'};    # Not tainted
          system "echo $abc";      # Is secure now!

          open(FOO,"$foo");        # OK
          open(FOO,">$foo");       # Not OK

          open(FOO,"echo $foo|");  # Not OK, but...
          open(FOO,"-|") || exec 'echo', $foo;    # OK

          $zzz = `echo $foo`;      # Insecure, zzz tainted

          unlink $abc,$foo;        # Insecure
          umask $foo;              # Insecure

          exec "echo $foo";        # Insecure
          exec "echo", $foo;       # Secure (doesn't use sh)
          exec "sh", '-c', $foo;   # Considered secure, alas

     The taintedness is associated with  each  scalar  value,  so
     some elements of an array can be tainted, and others not.

     If you try to do something insecure, you will  get  a  fatal
     error   saying   something  like  "Insecure  dependency"  or
     "Insecure PATH".  Note that you can still write an  insecure
     system  call or exec, but only by explicitly doing something
     like the last example above.  You can also bypass the taint-
     ing mechanism by referencing subpatterns--perl presumes that
     if you reference a substring using $1,  $2,  etc,  you  knew
     what you were doing when you wrote the pattern:

          $ARGV[0] =~ /^-P(\w+)$/;
          $printer = $1;      # Not tainted

     This is fairly secure since \w+ doesn't  match  shell  meta-
     characters.   Use  of  .+ would have been insecure, but perl
     doesn't check for that, so you must  be  careful  with  your
     patterns.   This  is  the ONLY mechanism for untainting user
     supplied filenames if you want to do file operations on them
     (unless you make $> equal to $<).

     It's also possible to get into trouble with other operations
     that don't care whether they use tainted values.  Make judi-
     cious use of the  file  tests  in  dealing  with  any  user-
     supplied  filenames.  When possible, do opens and such after
     setting $> = $<.  Perl  doesn't  prevent  you  from  opening
     tainted  filenames for reading, so be careful what you print
     out.  The tainting mechanism is intended to  prevent  stupid
     mistakes, not to remove the need for thought.

ENVIRONMENT
     Perl uses PATH in executing subprocesses, and in finding the
     script  if -S is used.  HOME or LOGDIR are used if chdir has
     no argument.

     Apart from these, perl uses no environment variables, except
     to  make them available to the script being executed, and to
     child processes.  However, scripts running setuid  would  do
     well  to  execute  the following lines before doing anything
     else, just to keep people honest:

         $ENV{'PATH'} = '/bin:/usr/bin';    # or whatever you need
         $ENV{'SHELL'} = '/bin/sh' if $ENV{'SHELL'} ne '';
         $ENV{'IFS'} = '' if $ENV{'IFS'} ne '';

AUTHOR
     Larry Wall <[e-mail]>
     MS-DOS port by Diomidis Spinellis <[e-mail]>
     Macintosh port by Matthias Neeracher <[e-mail]>

FILES
     /tmp/perl-eXXXXXX   temporary file for -e commands.

SEE ALSO
     a2p  awk to perl translator
     s2p  sed to perl translator

DIAGNOSTICS
     Compilation errors will tell you  the  line  number  of  the
     error,  with  an  indication of the next token or token type
     that was to be examined.  (In the case of a script passed to
     perl via -e switches, each -e is counted as one line.)

     Setuid scripts have additional constraints that can  produce
     error  messages such as "Insecure dependency".  See the sec-
     tion on setuid scripts.

TRAPS
     Accustomed awk users should take special note of the follow-
     ing:

     *   Semicolons are required after all simple  statements  in
         perl.  Newline is not a statement delimiter.

     *   Curly brackets are required on ifs and whiles.

     *   Variables begin with $ or @ in perl.

     *   Arrays index from 0 unless you set $[.  Likewise  string
         positions in substr() and index().

     *   You have to decide whether your  array  has  numeric  or
         string indices.

     *   Associative array values do not  spring  into  existence
         upon mere reference.

     *   You have to decide whether you want  to  use  string  or
         numeric comparisons.

     *   Reading an input line does not split it  for  you.   You
         get  to  split  it  yourself to an array.  And the split
         operator has different arguments.

     *   The current input line is normally in $_,  not  $0.   It
         generally  does  not  have the newline stripped.  ($0 is
         the name of the program executed.)

     *   $<digit> does not refer to  fields--it  refers  to  sub-
         strings matched by the last match pattern.

     *   The print  statement  does  not  add  field  and  record
         separators unless you set $, and $\.

     *   You must open your files before you print to them.

     *   The range operator  is  "..",  not  comma.   (The  comma
         operator works as in C.)

     *   The match operator is "=~", not "~".  ("~" is the  one's
         complement operator, as in C.)

     *   The exponentiation operator is "**", not "^".   ("^"  is
         the XOR operator, as in C.)

     *   The concatenation operator is ".", not the null  string.
         (Using  the  null  string  would  render  "/pat/  /pat/"
         unparsable, since the third slash would  be  interpreted
         as  a division operator--the tokener is in fact slightly
         context sensitive for operators like /, ?, and  <.   And
         in fact, . itself can be the beginning of a number.)

     *   Next, exit and continue work differently.

     *   The following variables work differently

                Awk               Perl
                ARGC              $#ARGV
                ARGV[0]           $0
                FILENAME          $ARGV
                FNR               $. - something
                FS                (whatever you like)
                NF                $#Fld, or some such
                NR                $.
                OFMT              $#
                OFS               $,
                ORS               $\
                RLENGTH           length($&)
                RS                $/
                RSTART            length($`)
                SUBSEP            $;

     *   When in doubt, run the awk construct through a2p and see
         what it gives you.

     Cerebral C programmers should take note of the following:

     *   Curly brackets are required on ifs and whiles.

     *   You should use "elsif" rather than "else if"

     *   Break and continue become last and next, respectively.

     *   There's no switch statement.

     *   Variables begin with $ or @ in perl.

     *   Printf does not implement *.

     *   Comments begin with #, not /*.

     *   You can't take the address of anything.

     *   ARGV must be capitalized.

     *   The "system" calls link,  unlink,  rename,  etc.  return
         nonzero for success, not 0.

     *   Signal handlers deal with signal names, not numbers.

     Seasoned sed programmers should take note of the following:

     *   Backreferences in substitutions use $ rather than \.

     *   The pattern matching metacharacters (, ), and |  do  not
         have backslashes in front.

     *   The range operator is .. rather than comma.

     Sharp shell programmers should take note of the following:

     *   The  backtick  operator  does  variable   interpretation
         without  regard  to the presence of single quotes in the
         command.

     *   The backtick operator does no translation of the  return
         value, unlike csh.

     *   Shells (especially csh) do several levels  of  substitu-
         tion  on each command line.  Perl does substitution only
         in certain constructs such as double quotes,  backticks,
         angle brackets and search patterns.

     *   Shells interpret scripts a little bit at a  time.   Perl
         compiles the whole program before executing it.

     *   The arguments are available via @ARGV, not $1, $2, etc.

     *   The environment is not automatically made  available  as
         variables.

ERRATA AND ADDENDA
     The Perl book, Programming Perl , has  the  following  omis-
     sions and goofs.

     On page 5, the examples which read

          eval "/usr/bin/perl

     should read

          eval "exec /usr/bin/perl

     On page 195, the equivalent to the System V sum program only
     works for very small files.  To do larger files, use

          undef $/;

          $checksum = unpack("%32C*",<>) % 32767;

     The  descriptions  of  alarm  and  sleep  refer  to   signal
     SIGALARM.  These should refer to SIGALRM.

     The -0 switch to set the initial value of $/  was  added  to
     Perl after the book went to press.

     The -l switch now does automatic line ending processing.

     The qx// construct is now a synonym for backticks.

     $0 may now be assigned to set the argument displayed  by  ps
     (1).

     The new @###.## format was  omitted  accidentally  from  the
     description on formats.

     It wasn't known at press time that  s///ee  caused  multiple
     evaluations  of  the  replacement expression.  This is to be
     construed as a feature.

     (LIST) x $count now does array replication.

     There is now no limit on the number of parentheses in a reg-
     ular expression.

     In double-quote context, more escapes are supported: \e, \a,
     \x1b,  \c[,  \l,  \L,  \u,  \U, \E.  The latter five control
     up/lower case translation.

     The $/ variable may now be set to a  multi-character  delim-
     iter.

     There is now a g modifier on ordinary pattern matching  that
     causes  it  to  iterate  through  a  string finding multiple
     matches.

     All of the $^X variables are new except for $^T.

     The  default  top-of-form  format  for  FILEHANDLE  is   now
     FILEHANDLE_TOP rather than top.

     The eval {} and sort {} constructs  were  added  in  version
     4.018.

     The v and V (little-endian) template options  for  pack  and
     unpack were added in 4.019.

BUGS
     Perl is at the mercy of your machine's definitions of  vari-
     ous operations such as type casting, atof() and sprintf().

     If your stdio requires an seek  or  eof  between  reads  and
     writes  on a particular stream, so does perl.  (This doesn't
     apply to sysread() and syswrite().)

     While none of the built-in data  types  have  any  arbitrary
     size  limits (apart from memory size), there are still a few
     arbitrary limits: a given identifier may not be longer  than
     255  characters, and no component of your PATH may be longer
     than 255 if you use -S.

     Perl actually stands  for  Pathologically  Eclectic  Rubbish
     Lister, but don't tell anyone I said that.