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PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 1 PERL(1) USER COMMANDS PERL(1) 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: + .TP 5 -0digits specifies the record separator ($/) as an octal number. If there are no digits, the null character is the separator. Other switches may precede or follow the digits. For example, if you have a version of find which can print filenames terminated by the null character, you can say this: find . -name '*.bak' -print0 | perl -n0e unlink The special value 00 will cause Perl to slurp files in para- graph mode. The value 0777 will cause Perl to slurp files whole since there is no legal character with that value. -a turns on autosplit mode when used with a -n or -p. An implicit split command to the @F array is done as the first thing inside the implicit while loop produced by the -n or -p. perl -ane 'print pop(@F), "\n";' is equivalent to while (<>) { @F = split(' '); print pop(@F), "\n"; } -c causes perl to check the syntax of the script and then exit without executing it. -d runs the script under the perl debugger. See the sec- tion on Debugging. -Dnumber Sun Release 4.1 Last change: 2 PERL(1) USER COMMANDS PERL(1) sets debugging flags. To watch how it executes your script, use -D14. (This only works if debugging is compiled into your perl.) Another nice value is -D1024, which lists your compiled syntax tree. And -D512 displays compiled regular expressions. -e commandline may be used to enter one line of script. Multiple -e commands may be given to build up a multi-line script. If -e is given, perl will not look for a script filename in the argument list. -iextension specifies that files processed by the <> construct are to be edited in-place. It does this by renaming the input file, opening the output file by the same name, and selecting that output file as the default for print statements. The extension, if supplied, is added to the name of the old file to make a backup copy. If no extension is supplied, no backup is made. Saying "perl -p -i.bak -e "s/foo/bar/;" ... " is the same as using the script: #!/usr/bin/perl -pi.bak s/foo/bar/; which is equivalent to #!/usr/bin/perl while (<>) { if ($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). Sun Release 4.1 Last change: 3 PERL(1) USER COMMANDS PERL(1) -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. -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 -ne 'chop;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. Sun Release 4.1 Last change: 4 PERL(1) USER COMMANDS PERL(1) #!/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. Sun Release 4.1 Last change: 5 PERL(1) USER COMMANDS PERL(1) -U allows perl to do unsafe operations. Currently the only "unsafe" operation is the unlinking of directories while running as superuser. -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. Sun Release 4.1 Last change: 6 PERL(1) USER COMMANDS PERL(1) 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 = (); Sun Release 4.1 Last change: 7 PERL(1) USER COMMANDS PERL(1) $#whatever = $[ - 1; If you evaluate an array in a scalar context, it returns the length of the array. The following is always true: @whatever == $#whatever - $[ + 1; 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. 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 Sun Release 4.1 Last change: 8 PERL(1) USER COMMANDS PERL(1) 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 Sun Release 4.1 Last change: 9 PERL(1) USER COMMANDS PERL(1) 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 oth- erwise 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 Sun Release 4.1 Last change: 10 PERL(1) USER COMMANDS PERL(1) 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); Sun Release 4.1 Last change: 11 PERL(1) USER COMMANDS PERL(1) 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: Sun Release 4.1 Last change: 12 PERL(1) USER COMMANDS PERL(1) 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.) Sun Release 4.1 Last change: 13 PERL(1) USER COMMANDS PERL(1) 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>; Sun Release 4.1 Last change: 14 PERL(1) USER COMMANDS PERL(1) 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. Typ- ically 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 Sun Release 4.1 Last change: 15 PERL(1) USER COMMANDS PERL(1) 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++; } Sun Release 4.1 Last change: 16 PERL(1) USER COMMANDS PERL(1) 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; } Sun Release 4.1 Last change: 17 PERL(1) USER COMMANDS PERL(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: Sun Release 4.1 Last change: 18 PERL(1) USER COMMANDS PERL(1) 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 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. Sun Release 4.1 Last change: 19 PERL(1) USER COMMANDS PERL(1) 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. print '-' x 80; # print row of dashes print '-' x80; # illegal, x80 is identifier print "\t" x ($tab/8), ' ' x ($tab%8); # tab over x= The repetition assignment operator. .. 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 Sun Release 4.1 Last change: 20 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 21 PERL(1) USER COMMANDS PERL(1) -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 Sun Release 4.1 Last change: 22 PERL(1) USER COMMANDS PERL(1) 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 Sun Release 4.1 Last change: 23 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 24 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 25 PERL(1) USER COMMANDS PERL(1) 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, Sun Release 4.1 Last change: 26 PERL(1) USER COMMANDS PERL(1) 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; Sun Release 4.1 Last change: 27 PERL(1) USER COMMANDS PERL(1) Here's an example of looking up non-numeric uids: 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 Sun Release 4.1 Last change: 28 PERL(1) USER COMMANDS PERL(1) 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 only have 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 Sun Release 4.1 Last change: 29 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 30 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 31 PERL(1) USER COMMANDS PERL(1) 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.) SUBROUTINE may be a scalar variable, in which case the variable contains the name of the subrou- tine to execute. The parentheses are required to avoid confusion with the "do EXPR" form. As an alternate 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 subroutine. The & form is also used to specify subroutines to the defined and undef operators. 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 Sun Release 4.1 Last change: 32 PERL(1) USER COMMANDS PERL(1) 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 Sun Release 4.1 Last change: 33 PERL(1) USER COMMANDS PERL(1) 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); } } Sun Release 4.1 Last change: 34 PERL(1) USER COMMANDS PERL(1) eval(EXPR) eval EXPR 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. 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: Sun Release 4.1 Last change: 35 PERL(1) USER COMMANDS PERL(1) $shell = '/bin/csh'; exec $shell '-sh'; # pretend it's a login shell exit(EXPR) 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 Sun Release 4.1 Last change: 36 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 37 PERL(1) USER COMMANDS PERL(1) # 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). getpwnam(NAME) 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 Sun Release 4.1 Last change: 38 PERL(1) USER COMMANDS PERL(1) 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: Sun Release 4.1 Last change: 39 PERL(1) USER COMMANDS PERL(1) ($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 Sun Release 4.1 Last change: 40 PERL(1) USER COMMANDS PERL(1) 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(). Sun Release 4.1 Last change: 41 PERL(1) USER COMMANDS PERL(1) 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: Sun Release 4.1 Last change: 42 PERL(1) USER COMMANDS PERL(1) @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. Sun Release 4.1 Last change: 43 PERL(1) USER COMMANDS PERL(1) 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(); } Sun Release 4.1 Last change: 44 PERL(1) USER COMMANDS PERL(1) 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/io /PATTERN/io 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 Sun Release 4.1 Last change: 45 PERL(1) USER COMMANDS PERL(1) 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 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. 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). Sun Release 4.1 Last change: 46 PERL(1) USER COMMANDS PERL(1) 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: Sun Release 4.1 Last change: 47 PERL(1) USER COMMANDS PERL(1) $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 { Sun Release 4.1 Last change: 48 PERL(1) USER COMMANDS PERL(1) 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 Sun Release 4.1 Last change: 49 PERL(1) USER COMMANDS PERL(1) 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 Sun Release 4.1 Last change: 50 PERL(1) USER COMMANDS PERL(1) 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. 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: Sun Release 4.1 Last change: 51 PERL(1) USER COMMANDS PERL(1) $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. Sun Release 4.1 Last change: 52 PERL(1) USER COMMANDS PERL(1) 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. FILEHAN- DLE may be a scalar variable name, in which case the variable contains the name of the filehandle, 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 argu- ments.) 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 expressions evaluated in an array context. Also be careful 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. Sun Release 4.1 Last change: 53 PERL(1) USER COMMANDS PERL(1) q/STRING/ qq/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. 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.'); $_ .= qq *** The previous line contains the naughty word "$&".\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 Sun Release 4.1 Last change: 54 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 55 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 56 PERL(1) USER COMMANDS PERL(1) 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 Sun Release 4.1 Last change: 57 PERL(1) USER COMMANDS PERL(1) 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. 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 Sun Release 4.1 Last change: 58 PERL(1) USER COMMANDS PERL(1) 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; } $rin = &fhbits('STDIN TTY SOCK'); The usual idiom is: Sun Release 4.1 Last change: 59 PERL(1) USER COMMANDS PERL(1) ($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. Sun Release 4.1 Last change: 60 PERL(1) USER COMMANDS PERL(1) 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 attach- ing 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, Sun Release 4.1 Last change: 61 PERL(1) USER COMMANDS PERL(1) 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 SIGALARM. Returns the number of seconds actually slept. 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 LIST Sorts the LIST and returns the sorted array value. Nonexistent values of arrays are stripped out. If SUBROUTINE is omitted, sorts in standard string com- parison order. If SUBROUTINE is specified, gives the name of a subroutine that returns an integer Sun Release 4.1 Last change: 62 PERL(1) USER COMMANDS PERL(1) less than, equal to, or greater than 0, depending on how the elements of the array are to be ordered. 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. SUBROUTINE may be a scalar variable name, in which case the value pro- vides the name of the subroutine to use. Examples: sub byage { $age{$a} - $age{$b}; # presuming integers } @sortedclass = sort byage @class; sub reverse { $a lt $b ? 1 : $a gt $b ? -1 : 0; } @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,$y); Example, assuming array lengths are passed before arrays: sub aeq { # compare two array values local(@a) = splice(@_,0,shift); local(@b) = splice(@_,0,shift); Sun Release 4.1 Last change: 63 PERL(1) USER COMMANDS PERL(1) return 0 unless @a == @b; # same len? while (@a) { return 0 if pop(@a) ne pop(@b); } return 1; } if (&aeq($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(/:/, $_, 3); (When assigning to a list, if LIMIT is omitted, perl supplies a LIMIT one larger than the number of vari- ables in the list, to avoid unnecessary work. For the list above LIMIT would have been 4 by default. In time critical applications it behooves you not to split into more fields than you really need.) Sun Release 4.1 Last change: 64 PERL(1) USER COMMANDS PERL(1) If the PATTERN contains parentheses, additional array elements are created from each matching sub- string in the delimiter. split(/([,-])/,"1-10,20"); produces the array value (1,'-',10,',',20) The pattern /PATTERN/ may be replaced with an expression to specify patterns that vary at runtime. (To do runtime compilation only once, use /$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 $_. srand(EXPR) srand EXPR Sets the random number seed for the rand operator. If EXPR is omitted, does srand(time). Sun Release 4.1 Last change: 65 PERL(1) USER COMMANDS PERL(1) stat(FILEHANDLE) stat FILEHANDLE stat(EXPR) stat SCALARVARIABLE Returns a 13-element array giving the statistics for a file, either the file opened via FILEHANDLE, or named by EXPR. Typically used as follows: ($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"; } 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 Sun Release 4.1 Last change: 66 PERL(1) USER COMMANDS PERL(1) producing entries before any line containing a cer- tain 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 set- ting $/ 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; $/ = "\177"; # something that doesn't occur 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 Sun Release 4.1 Last change: 67 PERL(1) USER COMMANDS PERL(1) 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. Sun Release 4.1 Last change: 68 PERL(1) USER COMMANDS PERL(1) 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; Sun Release 4.1 Last change: 69 PERL(1) USER COMMANDS PERL(1) 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