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PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) NNNNAAAAMMMMEEEE perlvar - Perl predefined variables DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN PPPPrrrreeeeddddeeeeffffiiiinnnneeeedddd NNNNaaaammmmeeeessss The following names have special meaning to Perl. Most of the punctuational names have reasonable mnemonics, or analogues in one of the shells. Nevertheless, if you wish to use the long variable names, you just need to say use English; at the top of your program. This will alias all the short names to the long names in the current package. Some of them even have medium names, generally borrowed from aaaawwwwkkkk. To go a step further, those variables that depend on the currently selected filehandle may instead be set by calling an object method on the FileHandle object. (Summary lines below for this contain the word HANDLE.) First you must say use FileHandle; after which you may use either method HANDLE EXPR or HANDLE->method(EXPR) Each of the methods returns the old value of the FileHandle attribute. The methods each take an optional EXPR, which if supplied specifies the new value for the FileHandle attribute in question. If not supplied, most of the methods do nothing to the current value, except for _a_u_t_o_f_l_u_s_h(), which will assume a 1 for you, just to be different. A few of these variables are considered "read-only". This means that if you try to assign to this variable, either directly or indirectly through a reference. If you attempt to do so, you'll raise a run-time exception. $ARG $_ The default input and pattern-searching space. The following pairs are equivalent: while (<>) {...} # only equivalent in while! while ($_ = <>) {...} Page 1 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) /^Subject:/ $_ =~ /^Subject:/ tr/a-z/A-Z/ $_ =~ tr/a-z/A-Z/ chop chop($_) (Mnemonic: underline is understood in certain operations.) $<_d_i_g_i_t> Contains the subpattern from the corresponding set of parentheses in the last pattern matched, not counting patterns matched in nested blocks that have been exited already. (Mnemonic: like \digit.) These variables are all read-only. $MATCH $& The string matched by the last successful pattern match (not counting any matches hidden within a BLOCK or _e_v_a_l() enclosed by the current BLOCK). (Mnemonic: like & in some editors.) This variable is read-only. $PREMATCH $` The string preceding whatever was matched by the last successful pattern match (not counting any matches hidden within a BLOCK or eval enclosed by the current BLOCK). (Mnemonic: ` often precedes a quoted string.) This variable is read-only. $POSTMATCH $' The string following whatever was matched by the last successful pattern match (not counting any matches hidden within a BLOCK or _e_v_a_l() enclosed by the current BLOCK). (Mnemonic: ' often follows a quoted string.) Example: $_ = 'abcdefghi'; /def/; print "$`:$&:$'\n"; # prints abc:def:ghi This variable is read-only. $LAST_PAREN_MATCH Page 2 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) $+ The last bracket matched by the last search pattern. This is useful if you don't know which of a set of alternative patterns matched. For example: /Version: (.*)|Revision: (.*)/ && ($rev = $+); (Mnemonic: be positive and forward looking.) This variable is read-only. $MULTILINE_MATCHING $* Set to 1 to do multiline matching within a string, 0 to tell Perl that it can assume that strings contain a single line, for the purpose of optimizing pattern matches. Pattern matches on strings containing multiple newlines can produce confusing results when "$*" is 0. Default is 0. (Mnemonic: * matches multiple things.) Note that this variable only influences the interpretation of "^" and "$". A literal newline can be searched for even when $* == 0. Use of "$*" is deprecated in Perl 5. input_line_number HANDLE EXPR $INPUT_LINE_NUMBER $NR $. The current input line number of the last filehandle that was read. This variable should be considered read-only. Remember that only an explicit close on the filehandle resets the line number. Since "<>" never does an explicit close, line numbers increase across ARGV files (but see examples under _e_o_f()). (Mnemonic: many programs use "." to mean the current line number.) input_record_separator HANDLE EXPR $INPUT_RECORD_SEPARATOR $RS $/ The input record separator, newline by default. Works like aaaawwwwkkkk's RS variable, including treating blank lines as delimiters if set to the null string. You may set it to a multicharacter string to match a multi-character delimiter. Note that setting it to "\n\n" means something slightly different than setting it to "", if the file contains consecutive Page 3 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) blank lines. Setting it to "" will treat two or more consecutive blank lines as a single blank line. Setting it to "\n\n" will blindly assume that the next input character belongs to the next paragraph, even if it's a newline. (Mnemonic: / is used to delimit line boundaries when quoting poetry.) undef $/; $_ = <FH>; # whole file now here s/\n[ \t]+/ /g; autoflush HANDLE EXPR $OUTPUT_AUTOFLUSH $| If set to nonzero, forces a flush after every write or print on the currently selected output channel. Default is 0. Note that STDOUT will typically be line buffered if output is to the terminal and block buffered otherwise. Setting this variable is useful primarily when you are outputting to a pipe, such as when you are running a Perl script under rsh and want to see the output as it's happening. (Mnemonic: when you want your pipes to be piping hot.) output_field_separator HANDLE EXPR $OUTPUT_FIELD_SEPARATOR $OFS $, The output field separator for the print operator. Ordinarily the print operator simply prints out the comma separated fields you specify. In order to get behavior more like aaaawwwwkkkk, set this variable as you would set aaaawwwwkkkk's OFS variable to specify what is printed between fields. (Mnemonic: what is printed when there is a , in your print statement.) output_record_separator HANDLE EXPR $OUTPUT_RECORD_SEPARATOR $ORS $\ The output record separator for the print operator. Ordinarily the print operator simply prints out the comma separated fields you specify, with no trailing newline or record separator assumed. In order to get behavior more like aaaawwwwkkkk, set this variable as you Page 4 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) would set aaaawwwwkkkk's ORS variable to specify what is printed at the end of the print. (Mnemonic: you set "$\" instead of adding \n at the end of the print. Also, it's just like /, but it's what you get "back" from Perl.) $LIST_SEPARATOR $ This is like "$," except that it applies to array values interpolated into a double-quoted string (or similar interpreted string). Default is a space. (Mnemonic: obvious, I think.) $SUBSCRIPT_SEPARATOR $SUBSEP $; The subscript separator for multi-dimensional array emulation. If you refer to a hash element as $foo{$a,$b,$c} it really means $foo{join($;, $a, $b, $c)} But don't put @foo{$a,$b,$c} # a slice--note the @ which means ($foo{$a},$foo{$b},$foo{$c}) Default is "\034", the same as SUBSEP in aaaawwwwkkkk. Note that if your keys contain binary data there might not be any safe value for "$;". (Mnemonic: comma (the syntactic subscript separator) is a semi- semicolon. Yeah, I know, it's pretty lame, but "$," is already taken for something more important.) Consider using "real" multi-dimensional arrays in Perl 5. $OFMT $# The output format for printed numbers. This variable is a half-hearted attempt to emulate aaaawwwwkkkk's OFMT variable. There are times, however, when aaaawwwwkkkk and Perl have differing notions of what is in fact numeric. Also, the initial value is %.20g rather Page 5 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) than %.6g, so you need to set "$#" explicitly to get aaaawwwwkkkk's value. (Mnemonic: # is the number sign.) Use of "$#" is deprecated in Perl 5. format_page_number HANDLE EXPR $FORMAT_PAGE_NUMBER $% The current page number of the currently selected output channel. (Mnemonic: % is page number in nnnnrrrrooooffffffff.) format_lines_per_page HANDLE EXPR $FORMAT_LINES_PER_PAGE $= The current page length (printable lines) of the currently selected output channel. Default is 60. (Mnemonic: = has horizontal lines.) format_lines_left HANDLE EXPR $FORMAT_LINES_LEFT $- The number of lines left on the page of the currently selected output channel. (Mnemonic: lines_on_page - lines_printed.) format_name HANDLE EXPR $FORMAT_NAME $~ The name of the current report format for the currently selected output channel. Default is name of the filehandle. (Mnemonic: brother to "$^".) format_top_name HANDLE EXPR $FORMAT_TOP_NAME $^ The name of the current top-of-page format for the currently selected output channel. Default is name of the filehandle with _TOP appended. (Mnemonic: points to top of page.) format_line_break_characters HANDLE EXPR $FORMAT_LINE_BREAK_CHARACTERS $: The current set of characters after which a string may be broken to fill continuation fields (starting Page 6 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) with ^) in a format. Default is " \n-", to break on whitespace or hyphens. (Mnemonic: a "colon" in poetry is a part of a line.) format_formfeed HANDLE EXPR $FORMAT_FORMFEED $^L What formats output to perform a formfeed. Default is \f. $ACCUMULATOR $^A The current value of the _w_r_i_t_e() accumulator for _f_o_r_m_a_t() lines. A format contains _f_o_r_m_l_i_n_e() commands that put their result into $^A. After calling its format, _w_r_i_t_e() prints out the contents of $^A and empties. So you never actually see the contents of $^A unless you call _f_o_r_m_l_i_n_e() yourself and then look at it. See the _p_e_r_l_f_o_r_m manpage and the formline() entry in the _p_e_r_l_f_u_n_c manpage. $CHILD_ERROR $? The status returned by the last pipe close, backtick (``) command, or _s_y_s_t_e_m() operator. Note that this is the status word returned by the _w_a_i_t() system call, so the exit value of the subprocess is actually ($? >> 8). Thus on many systems, $? & 255 gives which signal, if any, the process died from, and whether there was a core dump. (Mnemonic: similar to sssshhhh and kkkksssshhhh.) $OS_ERROR $ERRNO $! If used in a numeric context, yields the current value of errno, with all the usual caveats. (This means that you shouldn't depend on the value of "$!" to be anything in particular unless you've gotten a specific error return indicating a system error.) If used in a string context, yields the corresponding system error string. You can assign to "$!" in order to set _e_r_r_n_o if, for instance, you want "$!" to return the string for error _n, or you want to set the exit value for the _d_i_e() operator. (Mnemonic: What just went bang?) $EVAL_ERROR Page 7 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) $@ The Perl syntax error message from the last _e_v_a_l() command. If null, the last _e_v_a_l() parsed and executed correctly (although the operations you invoked may have failed in the normal fashion). (Mnemonic: Where was the syntax error "at"?) $PROCESS_ID $PID $$ The process number of the Perl running this script. (Mnemonic: same as shells.) $REAL_USER_ID $UID $< The real uid of this process. (Mnemonic: it's the uid you came _F_R_O_M, if you're running setuid.) $EFFECTIVE_USER_ID $EUID $> The effective uid of this process. Example: $< = $>; # set real to effective uid ($<,$>) = ($>,$<); # swap real and effective uid (Mnemonic: it's the uid you went _T_O, if you're running setuid.) Note: "$<" and "$>" can only be swapped on machines supporting _s_e_t_r_e_u_i_d(). $REAL_GROUP_ID $GID $( The real gid of this process. If you are on a machine that supports membership in multiple groups simultaneously, gives a space separated list of groups you are in. The first number is the one returned by _g_e_t_g_i_d(), and the subsequent ones by _g_e_t_g_r_o_u_p_s(), one of which may be the same as the first number. (Mnemonic: parentheses are used to _G_R_O_U_P things. The real gid is the group you _L_E_F_T, if you're running setgid.) $EFFECTIVE_GROUP_ID $EGID Page 8 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) $) The effective gid of this process. If you are on a machine that supports membership in multiple groups simultaneously, gives a space separated list of groups you are in. The first number is the one returned by _g_e_t_e_g_i_d(), and the subsequent ones by _g_e_t_g_r_o_u_p_s(), one of which may be the same as the first number. (Mnemonic: parentheses are used to _G_R_O_U_P things. The effective gid is the group that's _R_I_G_H_T for you, if you're running setgid.) Note: "$<", "$>", "$(" and "$)" can only be set on machines that support the corresponding _s_e_t[_r_e][_u_g]_i_d() routine. "$(" and "$)" can only be swapped on machines supporting _s_e_t_r_e_g_i_d(). $PROGRAM_NAME $0 Contains the name of the file containing the Perl script being executed. Assigning to "$0" modifies the argument area that the _p_s(1) program sees. This is more useful as a way of indicating the current program state than it is for hiding the program you're running. (Mnemonic: same as sssshhhh and kkkksssshhhh.) $[ The index of the first element in an array, and of the first character in a substring. Default is 0, but you could set it to 1 to make Perl behave more like aaaawwwwkkkk (or Fortran) when subscripting and when evaluating the _i_n_d_e_x() and _s_u_b_s_t_r() functions. (Mnemonic: [ begins subscripts.) As of Perl 5, assignment to "$[" is treated as a compiler directive, and cannot influence the behavior of any other file. Its use is discouraged. $PERL_VERSION $] The string printed out when you say perl -v. It can be used to determine at the beginning of a script whether the perl interpreter executing the script is in the right range of versions. If used in a numeric context, returns the version + patchlevel / 1000. Example: # see if getc is available ($version,$patchlevel) = $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/; print STDERR "(No filename completion available.)\n" if $version * 1000 + $patchlevel < 2016; or, used numerically, Page 9 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) warn "No checksumming!\n" if $] < 3.019; (Mnemonic: Is this version of perl in the right bracket?) $DEBUGGING $^D The current value of the debugging flags. (Mnemonic: value of ----DDDD switch.) $SYSTEM_FD_MAX $^F The maximum system file descriptor, ordinarily 2. System file descriptors are passed to _e_x_e_c()ed processes, while higher file descriptors are not. Also, during an _o_p_e_n(), system file descriptors are preserved even if the _o_p_e_n() fails. (Ordinary file descriptors are closed before the _o_p_e_n() is attempted.) Note that the close-on-exec status of a file descriptor will be decided according to the value of $^F at the time of the open, not the time of the exec. $INPLACE_EDIT $^I The current value of the inplace-edit extension. Use undef to disable inplace editing. (Mnemonic: value of ----iiii switch.) $PERLDB $^P The internal flag that the debugger clears so that it doesn't debug itself. You could conceivable disable debugging yourself by clearing it. $BASETIME $^T The time at which the script began running, in seconds since the epoch (beginning of 1970). The values returned by the ----MMMM, ----AAAA and ----CCCC filetests are based on this value. $WARNING $^W The current value of the warning switch, either TRUE or FALSE. (Mnemonic: related to the ----wwww switch.) $EXECUTABLE_NAME $^X The name that the Perl binary itself was executed as, from C's argv[0]. Page 10 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) $ARGV contains the name of the current file when reading from <>. @ARGV The array @ARGV contains the command line arguments intended for the script. Note that $#ARGV is the generally number of arguments minus one, since $ARGV[0] is the first argument, _N_O_T the command name. See "$0" for the command name. @INC The array @INC contains the list of places to look for Perl scripts to be evaluated by the do EXPR, require, or use constructs. It initially consists of the arguments to any ----IIII command line switches, followed by the default Perl library, probably "/usr/local/lib/perl", followed by ".", to represent the current directory. %INC The hash %INC contains entries for each filename that has been included via do or require. The key is the filename you specified, and the value is the location of the file actually found. The require command uses this array to determine whether a given file has already been included. $ENV{expr} The hash %ENV contains your current environment. Setting a value in ENV changes the environment for child processes. $SIG{expr} The hash %SIG is used to set signal handlers for various signals. Example: sub handler { # 1st argument is signal name local($sig) = @_; print "Caught a SIG$sig--shutting down\n"; close(LOG); exit(0); } $SIG{'INT'} = 'handler'; $SIG{'QUIT'} = 'handler'; ... $SIG{'INT'} = 'DEFAULT'; # restore default action $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT The %SIG array only contains values for the signals actually set within the Perl script. Here are some other examples: Page 11 (printed 6/30/95) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLVVVVAAAARRRR((((1111)))) $SIG{PIPE} = Plumber; # SCARY!! $SIG{"PIPE"} = "Plumber"; # just fine, assumes main::Plumber $SIG{"PIPE"} = \&Plumber; # just fine; assume current Plumber $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return?? The one marked scary is problematic because it's a bareword, which means sometimes it's a string representing the function, and sometimes it's going to call the subroutine call right then and there! Best to be sure and quote it or take a reference to it. *Plumber works too. See <perlsubs>. Page 12 (printed 6/30/95)