3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTuUWX> ]>
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 Activeware port of Perl,
134 will modify the Registry to associate the F<.pl> extension with the perl
135 interpreter. If you install another port of Perl, including the one
136 in the Win32 directory of the Perl distribution, then you'll have to
137 modify the Registry yourself. Note that this means you can no
138 longer tell the difference between an executable Perl program
139 and a Perl library file.
143 A Macintosh perl program will have the appropriate Creator and
144 Type, so that double-clicking them will invoke the perl application.
150 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
151 $ exit++ + ++$status != 0 and $exit = $status = undef;
153 at the top of your program, where B<-mysw> are any command line switches you
154 want to pass to Perl. You can now invoke the program directly, by saying
155 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
156 via F<DCL$PATH> by just using the name of the program).
158 This incantation is a bit much to remember, but Perl will display it for
159 you if you say C<perl "-V:startperl">.
163 Command-interpreters on non-Unix systems have rather different ideas
164 on quoting than Unix shells. You'll need to learn the special
165 characters in your command-interpreter (C<*>, C<\> and C<"> are
166 common) and how to protect whitespace and these characters to run
167 one-liners (see B<-e> below).
169 On some systems, you may have to change single-quotes to double ones,
170 which you must I<not> do on Unix or Plan9 systems. You might also
171 have to change a single % to a %%.
176 perl -e 'print "Hello world\n"'
179 perl -e "print \"Hello world\n\""
182 print "Hello world\n"
183 (then Run "Myscript" or Shift-Command-R)
186 perl -e "print ""Hello world\n"""
188 The problem is that none of this is reliable: it depends on the
189 command and it is entirely possible neither works. If B<4DOS> were
190 the command shell, this would probably work better:
192 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
194 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
195 when nobody was looking, but just try to find documentation for its
198 Under the Macintosh, it depends which environment you are using. The MacPerl
199 shell, or MPW, is much like Unix shells in its support for several
200 quoting variants, except that it makes free use of the Macintosh's non-ASCII
201 characters as control characters.
203 There is no general solution to all of this. It's just a mess.
205 =head2 Location of Perl
207 It may seem obvious to say, but Perl is useful only when users can
208 easily find it. When possible, it's good for both F</usr/bin/perl>
209 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
210 that can't be done, system administrators are strongly encouraged
211 to put (symlinks to) perl and its accompanying utilities into a
212 directory typically found along a user's PATH, or in some other
213 obvious and convenient place.
215 In this documentation, C<#!/usr/bin/perl> on the first line of the program
216 will stand in for whatever method works on your system. You are
217 advised to use a specific path if you care about a specific version.
219 #!/usr/local/bin/perl5.00554
221 or if you just want to be running at least version, place a statement
222 like this at the top of your program:
226 =head2 Command Switches
228 As with all standard commands, a single-character switch may be
229 clustered with the following switch, if any.
231 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
237 =item B<-0>[I<digits>]
239 specifies the input record separator (C<$/>) as an octal number. If there are
240 no digits, the null character is the separator. Other switches may
241 precede or follow the digits. For example, if you have a version of
242 B<find> which can print filenames terminated by the null character, you
245 find . -name '*.orig' -print0 | perl -n0e unlink
247 The special value 00 will cause Perl to slurp files in paragraph mode.
248 The value 0777 will cause Perl to slurp files whole because there is no
249 legal character with that value.
253 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
254 split command to the @F array is done as the first thing inside the
255 implicit while loop produced by the B<-n> or B<-p>.
257 perl -ane 'print pop(@F), "\n";'
266 An alternate delimiter may be specified using B<-F>.
270 causes Perl to check the syntax of the program and then exit without
271 executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
272 because these are considered as occurring outside the execution of
273 your program. C<INIT> blocks, however, will be skipped.
277 runs the program under the Perl debugger. See L<perldebug>.
281 runs the program under the control of a debugging, profiling, or
282 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
283 the program using the Devel::DProf profiler. See L<perldebug>.
285 =item B<-D>I<letters>
289 sets debugging flags. To watch how it executes your program, use
290 B<-Dtls>. (This works only if debugging is compiled into your
291 Perl.) Another nice value is B<-Dx>, which lists your compiled
292 syntax tree. And B<-Dr> displays compiled regular expressions. As an
293 alternative, specify a number instead of list of letters (e.g., B<-D14> is
294 equivalent to B<-Dtls>):
296 1 p Tokenizing and parsing
298 4 l Context (loop) stack processing
300 16 o Method and overloading resolution
301 32 c String/numeric conversions
302 64 P Print preprocessor command for -P
303 128 m Memory allocation
304 256 f Format processing
305 512 r Regular expression parsing and execution
306 1024 x Syntax tree dump
307 2048 u Tainting checks
308 4096 L Memory leaks (needs -DLEAKTEST when compiling Perl)
309 8192 H Hash dump -- usurps values()
310 16384 X Scratchpad allocation
312 65536 S Thread synchronization
314 All these flags require B<-DDEBUGGING> when you compile the Perl
315 executable. See the F<INSTALL> file in the Perl source distribution
316 for how to do this. This flag is automatically set if you include B<-g>
317 option when C<Configure> asks you about optimizer/debugger flags.
319 If you're just trying to get a print out of each line of Perl code
320 as it executes, the way that C<sh -x> provides for shell scripts,
321 you can't use Perl's B<-D> switch. Instead do this
323 # Bourne shell syntax
324 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
327 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
329 See L<perldebug> for details and variations.
331 =item B<-e> I<commandline>
333 may be used to enter one line of program. If B<-e> is given, Perl
334 will not look for a filename in the argument list. Multiple B<-e>
335 commands may be given to build up a multi-line script. Make sure
336 to use semicolons where you would in a normal program.
338 =item B<-F>I<pattern>
340 specifies the pattern to split on if B<-a> is also in effect. The
341 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
342 put in single quotes.
346 prints a summary of the options.
348 =item B<-i>[I<extension>]
350 specifies that files processed by the C<E<lt>E<gt>> construct are to be
351 edited in-place. It does this by renaming the input file, opening the
352 output file by the original name, and selecting that output file as the
353 default for print() statements. The extension, if supplied, is used to
354 modify the name of the old file to make a backup copy, following these
357 If no extension is supplied, no backup is made and the current file is
360 If the extension doesn't contain a C<*>, then it is appended to the
361 end of the current filename as a suffix. If the extension does
362 contain one or more C<*> characters, then each C<*> is replaced
363 with the current filename. In Perl terms, you could think of this
366 ($backup = $extension) =~ s/\*/$file_name/g;
368 This allows you to add a prefix to the backup file, instead of (or in
369 addition to) a suffix:
371 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
373 Or even to place backup copies of the original files into another
374 directory (provided the directory already exists):
376 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
378 These sets of one-liners are equivalent:
380 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
381 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
383 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
384 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
386 From the shell, saying
388 $ perl -p -i.orig -e "s/foo/bar/; ... "
390 is the same as using the program:
392 #!/usr/bin/perl -pi.orig
395 which is equivalent to
398 $extension = '.orig';
400 if ($ARGV ne $oldargv) {
401 if ($extension !~ /\*/) {
402 $backup = $ARGV . $extension;
405 ($backup = $extension) =~ s/\*/$ARGV/g;
407 rename($ARGV, $backup);
408 open(ARGVOUT, ">$ARGV");
415 print; # this prints to original filename
419 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
420 know when the filename has changed. It does, however, use ARGVOUT for
421 the selected filehandle. Note that STDOUT is restored as the default
422 output filehandle after the loop.
424 As shown above, Perl creates the backup file whether or not any output
425 is actually changed. So this is just a fancy way to copy files:
427 $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3...
429 $ perl -p -i '.orig' -e 1 file1 file2 file3...
431 You can use C<eof> without parentheses to locate the end of each input
432 file, in case you want to append to each file, or reset line numbering
433 (see example in L<perlfunc/eof>).
435 If, for a given file, Perl is unable to create the backup file as
436 specified in the extension then it will skip that file and continue on
437 with the next one (if it exists).
439 For a discussion of issues surrounding file permissions and B<-i>,
440 see L<perlfaq5/Why does Perl let me delete read-only files? Why
441 does -i clobber protected files? Isn't this a bug in Perl?>.
443 You cannot use B<-i> to create directories or to strip extensions from
446 Perl does not expand C<~> in filenames, which is good, since some
447 folks use it for their backup files:
449 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
451 Finally, the B<-i> switch does not impede execution when no
452 files are given on the command line. In this case, no backup is made
453 (the original file cannot, of course, be determined) and processing
454 proceeds from STDIN to STDOUT as might be expected.
456 =item B<-I>I<directory>
458 Directories specified by B<-I> are prepended to the search path for
459 modules (C<@INC>), and also tells the C preprocessor where to search for
460 include files. The C preprocessor is invoked with B<-P>; by default it
461 searches /usr/include and /usr/lib/perl.
463 =item B<-l>[I<octnum>]
465 enables automatic line-ending processing. It has two separate
466 effects. First, it automatically chomps C<$/> (the input record
467 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
468 (the output record separator) to have the value of I<octnum> so
469 that any print statements will have that separator added back on.
470 If I<octnum> is omitted, sets C<$\> to the current value of
471 C<$/>. For instance, to trim lines to 80 columns:
473 perl -lpe 'substr($_, 80) = ""'
475 Note that the assignment C<$\ = $/> is done when the switch is processed,
476 so the input record separator can be different than the output record
477 separator if the B<-l> switch is followed by a B<-0> switch:
479 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
481 This sets C<$\> to newline and then sets C<$/> to the null character.
483 =item B<-m>[B<->]I<module>
485 =item B<-M>[B<->]I<module>
487 =item B<-M>[B<->]I<'module ...'>
489 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
491 B<-m>I<module> executes C<use> I<module> C<();> before executing your
494 B<-M>I<module> executes C<use> I<module> C<;> before executing your
495 program. You can use quotes to add extra code after the module name,
496 e.g., C<'-Mmodule qw(foo bar)'>.
498 If the first character after the B<-M> or B<-m> is a dash (C<->)
499 then the 'use' is replaced with 'no'.
501 A little builtin syntactic sugar means you can also say
502 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
503 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
504 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
505 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
506 removes the distinction between B<-m> and B<-M>.
510 causes Perl to assume the following loop around your program, which
511 makes it iterate over filename arguments somewhat like B<sed -n> or
516 ... # your program goes here
519 Note that the lines are not printed by default. See B<-p> to have
520 lines printed. If a file named by an argument cannot be opened for
521 some reason, Perl warns you about it and moves on to the next file.
523 Here is an efficient way to delete all files older than a week:
525 find . -mtime +7 -print | perl -nle unlink
527 This is faster than using the B<-exec> switch of B<find> because you don't
528 have to start a process on every filename found. It does suffer from
529 the bug of mishandling newlines in pathnames, which you can fix if
532 C<BEGIN> and C<END> blocks may be used to capture control before or after
533 the implicit program loop, just as in B<awk>.
537 causes Perl to assume the following loop around your program, which
538 makes it iterate over filename arguments somewhat like B<sed>:
543 ... # your program goes here
545 print or die "-p destination: $!\n";
548 If a file named by an argument cannot be opened for some reason, Perl
549 warns you about it, and moves on to the next file. Note that the
550 lines are printed automatically. An error occurring during printing is
551 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
552 overrides a B<-n> switch.
554 C<BEGIN> and C<END> blocks may be used to capture control before or after
555 the implicit loop, just as in B<awk>.
559 causes your program to be run through the C preprocessor before
560 compilation by Perl. (Because both comments and B<cpp> directives begin
561 with the # character, you should avoid starting comments with any words
562 recognized by the C preprocessor such as "if", "else", or "define".)
566 enables rudimentary switch parsing for switches on the command
567 line after the program name but before any filename arguments (or before
568 a B<-->). Any switch found there is removed from @ARGV and sets the
569 corresponding variable in the Perl program. The following program
570 prints "true" if and only if the program is invoked with a B<-xyz> switch.
573 if ($xyz) { print "true\n" }
577 makes Perl use the PATH environment variable to search for the
578 program (unless the name of the program contains directory separators).
580 On some platforms, this also makes Perl append suffixes to the
581 filename while searching for it. For example, on Win32 platforms,
582 the ".bat" and ".cmd" suffixes are appended if a lookup for the
583 original name fails, and if the name does not already end in one
584 of those suffixes. If your Perl was compiled with DEBUGGING turned
585 on, using the -Dp switch to Perl shows how the search progresses.
587 Typically this is used to emulate #! startup on platforms that
588 don't support #!. This example works on many platforms that
589 have a shell compatible with Bourne shell:
592 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
593 if $running_under_some_shell;
595 The system ignores the first line and feeds the program to F</bin/sh>,
596 which proceeds to try to execute the Perl program as a shell script.
597 The shell executes the second line as a normal shell command, and thus
598 starts up the Perl interpreter. On some systems $0 doesn't always
599 contain the full pathname, so the B<-S> tells Perl to search for the
600 program if necessary. After Perl locates the program, it parses the
601 lines and ignores them because the variable $running_under_some_shell
602 is never true. If the program will be interpreted by csh, you will need
603 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
604 embedded spaces (and such) in the argument list. To start up sh rather
605 than csh, some systems may have to replace the #! line with a line
606 containing just a colon, which will be politely ignored by Perl. Other
607 systems can't control that, and need a totally devious construct that
608 will work under any of B<csh>, B<sh>, or Perl, such as the following:
610 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
611 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
612 if $running_under_some_shell;
614 If the filename supplied contains directory separators (i.e., is an
615 absolute or relative pathname), and if that file is not found,
616 platforms that append file extensions will do so and try to look
617 for the file with those extensions added, one by one.
619 On DOS-like platforms, if the program does not contain directory
620 separators, it will first be searched for in the current directory
621 before being searched for on the PATH. On Unix platforms, the
622 program will be searched for strictly on the PATH.
626 forces "taint" checks to be turned on so you can test them. Ordinarily
627 these checks are done only when running setuid or setgid. It's a
628 good idea to turn them on explicitly for programs that run on behalf
629 of someone else whom you might not necessarily trust, such as CGI
630 programs or any internet servers you might write in Perl. See
631 L<perlsec> for details. For security reasons, this option must be
632 seen by Perl quite early; usually this means it must appear early
633 on the command line or in the #! line for systems which support
638 This obsolete switch causes Perl to dump core after compiling your
639 program. You can then in theory take this core dump and turn it
640 into an executable file by using the B<undump> program (not supplied).
641 This speeds startup at the expense of some disk space (which you
642 can minimize by stripping the executable). (Still, a "hello world"
643 executable comes out to about 200K on my machine.) If you want to
644 execute a portion of your program before dumping, use the dump()
645 operator instead. Note: availability of B<undump> is platform
646 specific and may not be available for a specific port of Perl.
648 This switch has been superseded in favor of the new Perl code
649 generator backends to the compiler. See L<B> and L<B::Bytecode>
654 allows Perl to do unsafe operations. Currently the only "unsafe"
655 operations are the unlinking of directories while running as superuser,
656 and running setuid programs with fatal taint checks turned into
657 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
658 be used along with this option to actually I<generate> the
659 taint-check warnings.
663 prints the version and patchlevel of your perl executable.
667 prints summary of the major perl configuration values and the current
672 Prints to STDOUT the value of the named configuration variable.
677 will provide strong clues about what your MANPATH variable should
678 be set to in order to access the Perl documentation.
682 prints warnings about dubious constructs, such as variable names
683 that are mentioned only once and scalar variables that are used
684 before being set, redefined subroutines, references to undefined
685 filehandles or filehandles opened read-only that you are attempting
686 to write on, values used as a number that doesn't look like numbers,
687 using an array as though it were a scalar, if your subroutines
688 recurse more than 100 deep, and innumerable other things.
690 This switch really just enables the internal C<^$W> variable. You
691 can disable or promote into fatal errors specific warnings using
692 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
693 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
694 facility is also available if you want to manipulate entire classes
695 of warnings; see L<warnings> (or better yet, its source code) about
700 Enables all warnings regardless of
705 Disables all warnings regardless of
708 =item B<-x> I<directory>
710 tells Perl that the program is embedded in a larger chunk of unrelated
711 ASCII text, such as in a mail message. Leading garbage will be
712 discarded until the first line that starts with #! and contains the
713 string "perl". Any meaningful switches on that line will be applied.
714 If a directory name is specified, Perl will switch to that directory
715 before running the program. The B<-x> switch controls only the
716 disposal of leading garbage. The program must be terminated with
717 C<__END__> if there is trailing garbage to be ignored (the program
718 can process any or all of the trailing garbage via the DATA filehandle
729 Used if chdir has no argument.
733 Used if chdir has no argument and HOME is not set.
737 Used in executing subprocesses, and in finding the program if B<-S> is
742 A colon-separated list of directories in which to look for Perl library
743 files before looking in the standard library and the current
744 directory. If PERL5LIB is not defined, PERLLIB is used. When running
745 taint checks (because the program was running setuid or setgid, or the
746 B<-T> switch was used), neither variable is used. The program should
749 use lib "/my/directory";
753 Command-line options (switches). Switches in this variable are taken
754 as if they were on every Perl command line. Only the B<-[DIMUdmw]>
755 switches are allowed. When running taint checks (because the program
756 was running setuid or setgid, or the B<-T> switch was used), this
757 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
758 enabled, and any subsequent options ignored.
762 A colon-separated list of directories in which to look for Perl library
763 files before looking in the standard library and the current directory.
764 If PERL5LIB is defined, PERLLIB is not used.
768 The command used to load the debugger code. The default is:
770 BEGIN { require 'perl5db.pl' }
772 =item PERL5SHELL (specific to the Win32 port)
774 May be set to an alternative shell that perl must use internally for
775 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
776 on WindowsNT and C<command.com /c> on Windows95. The value is considered
777 to be space-separated. Precede any character that needs to be protected
778 (like a space or backslash) with a backslash.
780 Note that Perl doesn't use COMSPEC for this purpose because
781 COMSPEC has a high degree of variability among users, leading to
782 portability concerns. Besides, perl can use a shell that may not be
783 fit for interactive use, and setting COMSPEC to such a shell may
784 interfere with the proper functioning of other programs (which usually
785 look in COMSPEC to find a shell fit for interactive use).
787 =item PERL_DEBUG_MSTATS
789 Relevant only if perl is compiled with the malloc included with the perl
790 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
791 If set, this causes memory statistics to be dumped after execution. If set
792 to an integer greater than one, also causes memory statistics to be dumped
795 =item PERL_DESTRUCT_LEVEL
797 Relevant only if your perl executable was built with B<-DDEBUGGING>,
798 this controls the behavior of global destruction of objects and other
803 Perl also has environment variables that control how Perl handles data
804 specific to particular natural languages. See L<perllocale>.
806 Apart from these, Perl uses no other environment variables, except
807 to make them available to the program being executed, and to child
808 processes. However, programs running setuid would do well to execute
809 the following lines before doing anything else, just to keep people
812 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
813 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
814 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};