3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-CsTuUWX> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
20 The normal way to run a Perl program is by making it directly
21 executable, or else by passing the name of the source file as an
22 argument on the command line. (An interactive Perl environment
23 is also possible--see L<perldebug> for details on how to do that.)
24 Upon startup, Perl looks for your program in one of the following
31 Specified line by line via B<-e> switches on the command line.
35 Contained in the file specified by the first filename on the command line.
36 (Note that systems supporting the #! notation invoke interpreters this
37 way. See L<Location of Perl>.)
41 Passed in implicitly via standard input. This works only if there are
42 no filename arguments--to pass arguments to a STDIN-read program you
43 must explicitly specify a "-" for the program name.
47 With methods 2 and 3, Perl starts parsing the input file from the
48 beginning, unless you've specified a B<-x> switch, in which case it
49 scans for the first line starting with #! and containing the word
50 "perl", and starts there instead. This is useful for running a program
51 embedded in a larger message. (In this case you would indicate the end
52 of the program using the C<__END__> token.)
54 The #! line is always examined for switches as the line is being
55 parsed. Thus, if you're on a machine that allows only one argument
56 with the #! line, or worse, doesn't even recognize the #! line, you
57 still can get consistent switch behavior regardless of how Perl was
58 invoked, even if B<-x> was used to find the beginning of the program.
60 Because historically some operating systems silently chopped off
61 kernel interpretation of the #! line after 32 characters, some
62 switches may be passed in on the command line, and some may not;
63 you could even get a "-" without its letter, if you're not careful.
64 You probably want to make sure that all your switches fall either
65 before or after that 32-character boundary. Most switches don't
66 actually care if they're processed redundantly, but getting a "-"
67 instead of a complete switch could cause Perl to try to execute
68 standard input instead of your program. And a partial B<-I> switch
69 could also cause odd results.
71 Some switches do care if they are processed twice, for instance
72 combinations of B<-l> and B<-0>. Either put all the switches after
73 the 32-character boundary (if applicable), or replace the use of
74 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
76 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
77 The sequences "-*" and "- " are specifically ignored so that you could,
78 if you were so inclined, say
80 #!/bin/sh -- # -*- perl -*- -p
81 eval 'exec perl -wS $0 ${1+"$@"}'
82 if $running_under_some_shell;
84 to let Perl see the B<-p> switch.
86 A similar trick involves the B<env> program, if you have it.
90 The examples above use a relative path to the perl interpreter,
91 getting whatever version is first in the user's path. If you want
92 a specific version of Perl, say, perl5.005_57, you should place
93 that directly in the #! line's path.
95 If the #! line does not contain the word "perl", the program named after
96 the #! is executed instead of the Perl interpreter. This is slightly
97 bizarre, but it helps people on machines that don't do #!, because they
98 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
99 dispatch the program to the correct interpreter for them.
101 After locating your program, Perl compiles the entire program to an
102 internal form. If there are any compilation errors, execution of the
103 program is not attempted. (This is unlike the typical shell script,
104 which might run part-way through before finding a syntax error.)
106 If the program is syntactically correct, it is executed. If the program
107 runs off the end without hitting an exit() or die() operator, an implicit
108 C<exit(0)> is provided to indicate successful completion.
110 =head2 #! and quoting on non-Unix systems
112 Unix's #! technique can be simulated on other systems:
120 extproc perl -S -your_switches
122 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
127 Create a batch file to run your program, and codify it in
128 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
129 distribution for more information).
133 The Win95/NT installation, when using the ActiveState installer for Perl,
134 will modify the Registry to associate the F<.pl> extension with the perl
135 interpreter. If you install Perl by other means (including building from
136 the sources), you may have to modify the Registry yourself. Note that
137 this means you can no longer tell the difference between an executable
138 Perl program and a Perl library file.
142 A Macintosh perl program will have the appropriate Creator and
143 Type, so that double-clicking them will invoke the perl application.
149 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
150 $ exit++ + ++$status != 0 and $exit = $status = undef;
152 at the top of your program, where B<-mysw> are any command line switches you
153 want to pass to Perl. You can now invoke the program directly, by saying
154 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
155 via F<DCL$PATH> by just using the name of the program).
157 This incantation is a bit much to remember, but Perl will display it for
158 you if you say C<perl "-V:startperl">.
162 Command-interpreters on non-Unix systems have rather different ideas
163 on quoting than Unix shells. You'll need to learn the special
164 characters in your command-interpreter (C<*>, C<\> and C<"> are
165 common) and how to protect whitespace and these characters to run
166 one-liners (see B<-e> below).
168 On some systems, you may have to change single-quotes to double ones,
169 which you must I<not> do on Unix or Plan9 systems. You might also
170 have to change a single % to a %%.
175 perl -e 'print "Hello world\n"'
178 perl -e "print \"Hello world\n\""
181 print "Hello world\n"
182 (then Run "Myscript" or Shift-Command-R)
185 perl -e "print ""Hello world\n"""
187 The problem is that none of this is reliable: it depends on the
188 command and it is entirely possible neither works. If B<4DOS> were
189 the command shell, this would probably work better:
191 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
193 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
194 when nobody was looking, but just try to find documentation for its
197 Under the Macintosh, it depends which environment you are using. The MacPerl
198 shell, or MPW, is much like Unix shells in its support for several
199 quoting variants, except that it makes free use of the Macintosh's non-ASCII
200 characters as control characters.
202 There is no general solution to all of this. It's just a mess.
204 =head2 Location of Perl
206 It may seem obvious to say, but Perl is useful only when users can
207 easily find it. When possible, it's good for both F</usr/bin/perl>
208 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
209 that can't be done, system administrators are strongly encouraged
210 to put (symlinks to) perl and its accompanying utilities into a
211 directory typically found along a user's PATH, or in some other
212 obvious and convenient place.
214 In this documentation, C<#!/usr/bin/perl> on the first line of the program
215 will stand in for whatever method works on your system. You are
216 advised to use a specific path if you care about a specific version.
218 #!/usr/local/bin/perl5.00554
220 or if you just want to be running at least version, place a statement
221 like this at the top of your program:
225 =head2 Command Switches
227 As with all standard commands, a single-character switch may be
228 clustered with the following switch, if any.
230 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
236 =item B<-0>[I<digits>]
238 specifies the input record separator (C<$/>) as an octal number. If there are
239 no digits, the null character is the separator. Other switches may
240 precede or follow the digits. For example, if you have a version of
241 B<find> which can print filenames terminated by the null character, you
244 find . -name '*.orig' -print0 | perl -n0e unlink
246 The special value 00 will cause Perl to slurp files in paragraph mode.
247 The value 0777 will cause Perl to slurp files whole because there is no
248 legal character with that value.
252 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
253 split command to the @F array is done as the first thing inside the
254 implicit while loop produced by the B<-n> or B<-p>.
256 perl -ane 'print pop(@F), "\n";'
265 An alternate delimiter may be specified using B<-F>.
269 enables Perl to use the native wide character APIs on the target system.
270 The magic variable C<${^WIDE_SYSTEM_CALLS}> reflects the state of
271 this switch. See L<perlvar/"${^WIDE_SYSTEM_CALLS}">.
273 This feature is currently only implemented on the Win32 platform.
277 causes Perl to check the syntax of the program and then exit without
278 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
279 C<use> blocks, because these are considered as occurring outside the
280 execution of your program. C<INIT> and C<END> blocks, however, will
285 runs the program under the Perl debugger. See L<perldebug>.
289 runs the program under the control of a debugging, profiling, or
290 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
291 the program using the Devel::DProf profiler. See L<perldebug>.
293 =item B<-D>I<letters>
297 sets debugging flags. To watch how it executes your program, use
298 B<-Dtls>. (This works only if debugging is compiled into your
299 Perl.) Another nice value is B<-Dx>, which lists your compiled
300 syntax tree. And B<-Dr> displays compiled regular expressions. As an
301 alternative, specify a number instead of list of letters (e.g., B<-D14> is
302 equivalent to B<-Dtls>):
304 1 p Tokenizing and parsing
306 4 l Context (loop) stack processing
308 16 o Method and overloading resolution
309 32 c String/numeric conversions
310 64 P Print preprocessor command for -P
311 128 m Memory allocation
312 256 f Format processing
313 512 r Regular expression parsing and execution
314 1024 x Syntax tree dump
315 2048 u Tainting checks
316 4096 L Memory leaks (needs -DLEAKTEST when compiling Perl)
317 8192 H Hash dump -- usurps values()
318 16384 X Scratchpad allocation
320 65536 S Thread synchronization
322 All these flags require B<-DDEBUGGING> when you compile the Perl
323 executable. See the F<INSTALL> file in the Perl source distribution
324 for how to do this. This flag is automatically set if you include B<-g>
325 option when C<Configure> asks you about optimizer/debugger flags.
327 If you're just trying to get a print out of each line of Perl code
328 as it executes, the way that C<sh -x> provides for shell scripts,
329 you can't use Perl's B<-D> switch. Instead do this
331 # Bourne shell syntax
332 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
335 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
337 See L<perldebug> for details and variations.
339 =item B<-e> I<commandline>
341 may be used to enter one line of program. If B<-e> is given, Perl
342 will not look for a filename in the argument list. Multiple B<-e>
343 commands may be given to build up a multi-line script. Make sure
344 to use semicolons where you would in a normal program.
346 =item B<-F>I<pattern>
348 specifies the pattern to split on if B<-a> is also in effect. The
349 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
350 put in single quotes.
354 prints a summary of the options.
356 =item B<-i>[I<extension>]
358 specifies that files processed by the C<E<lt>E<gt>> construct are to be
359 edited in-place. It does this by renaming the input file, opening the
360 output file by the original name, and selecting that output file as the
361 default for print() statements. The extension, if supplied, is used to
362 modify the name of the old file to make a backup copy, following these
365 If no extension is supplied, no backup is made and the current file is
368 If the extension doesn't contain a C<*>, then it is appended to the
369 end of the current filename as a suffix. If the extension does
370 contain one or more C<*> characters, then each C<*> is replaced
371 with the current filename. In Perl terms, you could think of this
374 ($backup = $extension) =~ s/\*/$file_name/g;
376 This allows you to add a prefix to the backup file, instead of (or in
377 addition to) a suffix:
379 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
381 Or even to place backup copies of the original files into another
382 directory (provided the directory already exists):
384 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
386 These sets of one-liners are equivalent:
388 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
389 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
391 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
392 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
394 From the shell, saying
396 $ perl -p -i.orig -e "s/foo/bar/; ... "
398 is the same as using the program:
400 #!/usr/bin/perl -pi.orig
403 which is equivalent to
406 $extension = '.orig';
408 if ($ARGV ne $oldargv) {
409 if ($extension !~ /\*/) {
410 $backup = $ARGV . $extension;
413 ($backup = $extension) =~ s/\*/$ARGV/g;
415 rename($ARGV, $backup);
416 open(ARGVOUT, ">$ARGV");
423 print; # this prints to original filename
427 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
428 know when the filename has changed. It does, however, use ARGVOUT for
429 the selected filehandle. Note that STDOUT is restored as the default
430 output filehandle after the loop.
432 As shown above, Perl creates the backup file whether or not any output
433 is actually changed. So this is just a fancy way to copy files:
435 $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3...
437 $ perl -p -i '.orig' -e 1 file1 file2 file3...
439 You can use C<eof> without parentheses to locate the end of each input
440 file, in case you want to append to each file, or reset line numbering
441 (see example in L<perlfunc/eof>).
443 If, for a given file, Perl is unable to create the backup file as
444 specified in the extension then it will skip that file and continue on
445 with the next one (if it exists).
447 For a discussion of issues surrounding file permissions and B<-i>,
448 see L<perlfaq5/Why does Perl let me delete read-only files? Why
449 does -i clobber protected files? Isn't this a bug in Perl?>.
451 You cannot use B<-i> to create directories or to strip extensions from
454 Perl does not expand C<~> in filenames, which is good, since some
455 folks use it for their backup files:
457 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
459 Finally, the B<-i> switch does not impede execution when no
460 files are given on the command line. In this case, no backup is made
461 (the original file cannot, of course, be determined) and processing
462 proceeds from STDIN to STDOUT as might be expected.
464 =item B<-I>I<directory>
466 Directories specified by B<-I> are prepended to the search path for
467 modules (C<@INC>), and also tells the C preprocessor where to search for
468 include files. The C preprocessor is invoked with B<-P>; by default it
469 searches /usr/include and /usr/lib/perl.
471 =item B<-l>[I<octnum>]
473 enables automatic line-ending processing. It has two separate
474 effects. First, it automatically chomps C<$/> (the input record
475 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
476 (the output record separator) to have the value of I<octnum> so
477 that any print statements will have that separator added back on.
478 If I<octnum> is omitted, sets C<$\> to the current value of
479 C<$/>. For instance, to trim lines to 80 columns:
481 perl -lpe 'substr($_, 80) = ""'
483 Note that the assignment C<$\ = $/> is done when the switch is processed,
484 so the input record separator can be different than the output record
485 separator if the B<-l> switch is followed by a B<-0> switch:
487 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
489 This sets C<$\> to newline and then sets C<$/> to the null character.
491 =item B<-m>[B<->]I<module>
493 =item B<-M>[B<->]I<module>
495 =item B<-M>[B<->]I<'module ...'>
497 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
499 B<-m>I<module> executes C<use> I<module> C<();> before executing your
502 B<-M>I<module> executes C<use> I<module> C<;> before executing your
503 program. You can use quotes to add extra code after the module name,
504 e.g., C<'-Mmodule qw(foo bar)'>.
506 If the first character after the B<-M> or B<-m> is a dash (C<->)
507 then the 'use' is replaced with 'no'.
509 A little builtin syntactic sugar means you can also say
510 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
511 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
512 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
513 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
514 removes the distinction between B<-m> and B<-M>.
518 causes Perl to assume the following loop around your program, which
519 makes it iterate over filename arguments somewhat like B<sed -n> or
524 ... # your program goes here
527 Note that the lines are not printed by default. See B<-p> to have
528 lines printed. If a file named by an argument cannot be opened for
529 some reason, Perl warns you about it and moves on to the next file.
531 Here is an efficient way to delete all files older than a week:
533 find . -mtime +7 -print | perl -nle unlink
535 This is faster than using the B<-exec> switch of B<find> because you don't
536 have to start a process on every filename found. It does suffer from
537 the bug of mishandling newlines in pathnames, which you can fix if
540 C<BEGIN> and C<END> blocks may be used to capture control before or after
541 the implicit program loop, just as in B<awk>.
545 causes Perl to assume the following loop around your program, which
546 makes it iterate over filename arguments somewhat like B<sed>:
551 ... # your program goes here
553 print or die "-p destination: $!\n";
556 If a file named by an argument cannot be opened for some reason, Perl
557 warns you about it, and moves on to the next file. Note that the
558 lines are printed automatically. An error occurring during printing is
559 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
560 overrides a B<-n> switch.
562 C<BEGIN> and C<END> blocks may be used to capture control before or after
563 the implicit loop, just as in B<awk>.
567 causes your program to be run through the C preprocessor before
568 compilation by Perl. (Because both comments and B<cpp> directives begin
569 with the # character, you should avoid starting comments with any words
570 recognized by the C preprocessor such as "if", "else", or "define".)
574 enables rudimentary switch parsing for switches on the command
575 line after the program name but before any filename arguments (or before
576 a B<-->). Any switch found there is removed from @ARGV and sets the
577 corresponding variable in the Perl program. The following program
578 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
579 if it is invoked with B<-xyz=abc>.
582 if ($xyz) { print "$xyz\n" }
586 makes Perl use the PATH environment variable to search for the
587 program (unless the name of the program contains directory separators).
589 On some platforms, this also makes Perl append suffixes to the
590 filename while searching for it. For example, on Win32 platforms,
591 the ".bat" and ".cmd" suffixes are appended if a lookup for the
592 original name fails, and if the name does not already end in one
593 of those suffixes. If your Perl was compiled with DEBUGGING turned
594 on, using the -Dp switch to Perl shows how the search progresses.
596 Typically this is used to emulate #! startup on platforms that
597 don't support #!. This example works on many platforms that
598 have a shell compatible with Bourne shell:
601 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
602 if $running_under_some_shell;
604 The system ignores the first line and feeds the program to F</bin/sh>,
605 which proceeds to try to execute the Perl program as a shell script.
606 The shell executes the second line as a normal shell command, and thus
607 starts up the Perl interpreter. On some systems $0 doesn't always
608 contain the full pathname, so the B<-S> tells Perl to search for the
609 program if necessary. After Perl locates the program, it parses the
610 lines and ignores them because the variable $running_under_some_shell
611 is never true. If the program will be interpreted by csh, you will need
612 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
613 embedded spaces (and such) in the argument list. To start up sh rather
614 than csh, some systems may have to replace the #! line with a line
615 containing just a colon, which will be politely ignored by Perl. Other
616 systems can't control that, and need a totally devious construct that
617 will work under any of B<csh>, B<sh>, or Perl, such as the following:
619 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
620 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
621 if $running_under_some_shell;
623 If the filename supplied contains directory separators (i.e., is an
624 absolute or relative pathname), and if that file is not found,
625 platforms that append file extensions will do so and try to look
626 for the file with those extensions added, one by one.
628 On DOS-like platforms, if the program does not contain directory
629 separators, it will first be searched for in the current directory
630 before being searched for on the PATH. On Unix platforms, the
631 program will be searched for strictly on the PATH.
635 forces "taint" checks to be turned on so you can test them. Ordinarily
636 these checks are done only when running setuid or setgid. It's a
637 good idea to turn them on explicitly for programs that run on behalf
638 of someone else whom you might not necessarily trust, such as CGI
639 programs or any internet servers you might write in Perl. See
640 L<perlsec> for details. For security reasons, this option must be
641 seen by Perl quite early; usually this means it must appear early
642 on the command line or in the #! line for systems which support
647 This obsolete switch causes Perl to dump core after compiling your
648 program. You can then in theory take this core dump and turn it
649 into an executable file by using the B<undump> program (not supplied).
650 This speeds startup at the expense of some disk space (which you
651 can minimize by stripping the executable). (Still, a "hello world"
652 executable comes out to about 200K on my machine.) If you want to
653 execute a portion of your program before dumping, use the dump()
654 operator instead. Note: availability of B<undump> is platform
655 specific and may not be available for a specific port of Perl.
657 This switch has been superseded in favor of the new Perl code
658 generator backends to the compiler. See L<B> and L<B::Bytecode>
663 allows Perl to do unsafe operations. Currently the only "unsafe"
664 operations are the unlinking of directories while running as superuser,
665 and running setuid programs with fatal taint checks turned into
666 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
667 be used along with this option to actually I<generate> the
668 taint-check warnings.
672 prints the version and patchlevel of your perl executable.
676 prints summary of the major perl configuration values and the current
681 Prints to STDOUT the value of the named configuration variable.
686 will provide strong clues about what your MANPATH variable should
687 be set to in order to access the Perl documentation.
691 prints warnings about dubious constructs, such as variable names
692 that are mentioned only once and scalar variables that are used
693 before being set, redefined subroutines, references to undefined
694 filehandles or filehandles opened read-only that you are attempting
695 to write on, values used as a number that doesn't look like numbers,
696 using an array as though it were a scalar, if your subroutines
697 recurse more than 100 deep, and innumerable other things.
699 This switch really just enables the internal C<^$W> variable. You
700 can disable or promote into fatal errors specific warnings using
701 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
702 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
703 facility is also available if you want to manipulate entire classes
704 of warnings; see L<warnings> or L<perllexwarn>.
708 Enables all warnings regardless of C<no warnings> or C<$^W>.
713 Disables all warnings regardless of C<use warnings> or C<$^W>.
716 =item B<-x> I<directory>
718 tells Perl that the program is embedded in a larger chunk of unrelated
719 ASCII text, such as in a mail message. Leading garbage will be
720 discarded until the first line that starts with #! and contains the
721 string "perl". Any meaningful switches on that line will be applied.
722 If a directory name is specified, Perl will switch to that directory
723 before running the program. The B<-x> switch controls only the
724 disposal of leading garbage. The program must be terminated with
725 C<__END__> if there is trailing garbage to be ignored (the program
726 can process any or all of the trailing garbage via the DATA filehandle
737 Used if chdir has no argument.
741 Used if chdir has no argument and HOME is not set.
745 Used in executing subprocesses, and in finding the program if B<-S> is
750 A colon-separated list of directories in which to look for Perl library
751 files before looking in the standard library and the current
752 directory. Any architecture-specific directories under the specified
753 locations are automatically included if they exist. If PERL5LIB is not
754 defined, PERLLIB is used.
756 When running taint checks (either because the program was running setuid
757 or setgid, or the B<-T> switch was used), neither variable is used.
758 The program should instead say:
760 use lib "/my/directory";
764 Command-line options (switches). Switches in this variable are taken
765 as if they were on every Perl command line. Only the B<-[DIMUdmw]>
766 switches are allowed. When running taint checks (because the program
767 was running setuid or setgid, or the B<-T> switch was used), this
768 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
769 enabled, and any subsequent options ignored.
773 A colon-separated list of directories in which to look for Perl library
774 files before looking in the standard library and the current directory.
775 If PERL5LIB is defined, PERLLIB is not used.
779 The command used to load the debugger code. The default is:
781 BEGIN { require 'perl5db.pl' }
783 =item PERL5SHELL (specific to the Win32 port)
785 May be set to an alternative shell that perl must use internally for
786 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
787 on WindowsNT and C<command.com /c> on Windows95. The value is considered
788 to be space-separated. Precede any character that needs to be protected
789 (like a space or backslash) with a backslash.
791 Note that Perl doesn't use COMSPEC for this purpose because
792 COMSPEC has a high degree of variability among users, leading to
793 portability concerns. Besides, perl can use a shell that may not be
794 fit for interactive use, and setting COMSPEC to such a shell may
795 interfere with the proper functioning of other programs (which usually
796 look in COMSPEC to find a shell fit for interactive use).
798 =item PERL_DEBUG_MSTATS
800 Relevant only if perl is compiled with the malloc included with the perl
801 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
802 If set, this causes memory statistics to be dumped after execution. If set
803 to an integer greater than one, also causes memory statistics to be dumped
806 =item PERL_DESTRUCT_LEVEL
808 Relevant only if your perl executable was built with B<-DDEBUGGING>,
809 this controls the behavior of global destruction of objects and other
814 Perl also has environment variables that control how Perl handles data
815 specific to particular natural languages. See L<perllocale>.
817 Apart from these, Perl uses no other environment variables, except
818 to make them available to the program being executed, and to child
819 processes. However, programs running setuid would do well to execute
820 the following lines before doing anything else, just to keep people
823 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
824 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
825 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};