3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-CsTtuUWX> ]>
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 Plan 9 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>.
287 =item B<-d:>I<foo[=bar,baz]>
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. As with the B<-M>
292 flag, options may be passed to the Devel::foo package where they
293 will be received and interpreted by the Devel::foo::import routine.
294 The comma-separated list of options must follow a C<=> character.
297 =item B<-D>I<letters>
301 sets debugging flags. To watch how it executes your program, use
302 B<-Dtls>. (This works only if debugging is compiled into your
303 Perl.) Another nice value is B<-Dx>, which lists your compiled
304 syntax tree. And B<-Dr> displays compiled regular expressions;
305 the format of the output is explained in L<perldebguts>.
307 As an alternative, specify a number instead of list of letters (e.g.,
308 B<-D14> is equivalent to B<-Dtls>):
310 1 p Tokenizing and parsing
312 with v, displays all stacks
313 4 l Context (loop) stack processing
315 16 o Method and overloading resolution
316 32 c String/numeric conversions
317 64 P Print profiling info, preprocessor command for -P, source file input state
318 128 m Memory allocation
319 256 f Format processing
320 512 r Regular expression parsing and execution
321 1024 x Syntax tree dump
322 2048 u Tainting checks
323 4096 L Memory leaks (needs -DLEAKTEST when compiling Perl)
324 8192 H Hash dump -- usurps values()
325 16384 X Scratchpad allocation
327 65536 S Thread synchronization
329 262144 R Include reference counts of dumped variables (eg when using -Ds)
330 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
331 1048576 v Verbose: use in conjunction with other flags
333 All these flags require B<-DDEBUGGING> when you compile the Perl
334 executable (but see L<Devel::Peek>, L<re> which may change this).
335 See the F<INSTALL> file in the Perl source distribution
336 for how to do this. This flag is automatically set if you include B<-g>
337 option when C<Configure> asks you about optimizer/debugger flags.
339 If you're just trying to get a print out of each line of Perl code
340 as it executes, the way that C<sh -x> provides for shell scripts,
341 you can't use Perl's B<-D> switch. Instead do this
343 # If you have "env" utility
344 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
346 # Bourne shell syntax
347 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
350 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
352 See L<perldebug> for details and variations.
354 =item B<-e> I<commandline>
356 may be used to enter one line of program. If B<-e> is given, Perl
357 will not look for a filename in the argument list. Multiple B<-e>
358 commands may be given to build up a multi-line script. Make sure
359 to use semicolons where you would in a normal program.
361 =item B<-F>I<pattern>
363 specifies the pattern to split on if B<-a> is also in effect. The
364 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
365 put in single quotes.
369 prints a summary of the options.
371 =item B<-i>[I<extension>]
373 specifies that files processed by the C<E<lt>E<gt>> construct are to be
374 edited in-place. It does this by renaming the input file, opening the
375 output file by the original name, and selecting that output file as the
376 default for print() statements. The extension, if supplied, is used to
377 modify the name of the old file to make a backup copy, following these
380 If no extension is supplied, no backup is made and the current file is
383 If the extension doesn't contain a C<*>, then it is appended to the
384 end of the current filename as a suffix. If the extension does
385 contain one or more C<*> characters, then each C<*> is replaced
386 with the current filename. In Perl terms, you could think of this
389 ($backup = $extension) =~ s/\*/$file_name/g;
391 This allows you to add a prefix to the backup file, instead of (or in
392 addition to) a suffix:
394 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
396 Or even to place backup copies of the original files into another
397 directory (provided the directory already exists):
399 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
401 These sets of one-liners are equivalent:
403 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
404 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
406 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
407 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
409 From the shell, saying
411 $ perl -p -i.orig -e "s/foo/bar/; ... "
413 is the same as using the program:
415 #!/usr/bin/perl -pi.orig
418 which is equivalent to
421 $extension = '.orig';
423 if ($ARGV ne $oldargv) {
424 if ($extension !~ /\*/) {
425 $backup = $ARGV . $extension;
428 ($backup = $extension) =~ s/\*/$ARGV/g;
430 rename($ARGV, $backup);
431 open(ARGVOUT, ">$ARGV");
438 print; # this prints to original filename
442 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
443 know when the filename has changed. It does, however, use ARGVOUT for
444 the selected filehandle. Note that STDOUT is restored as the default
445 output filehandle after the loop.
447 As shown above, Perl creates the backup file whether or not any output
448 is actually changed. So this is just a fancy way to copy files:
450 $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3...
452 $ perl -p -i '.orig' -e 1 file1 file2 file3...
454 You can use C<eof> without parentheses to locate the end of each input
455 file, in case you want to append to each file, or reset line numbering
456 (see example in L<perlfunc/eof>).
458 If, for a given file, Perl is unable to create the backup file as
459 specified in the extension then it will skip that file and continue on
460 with the next one (if it exists).
462 For a discussion of issues surrounding file permissions and B<-i>,
463 see L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>.
465 You cannot use B<-i> to create directories or to strip extensions from
468 Perl does not expand C<~> in filenames, which is good, since some
469 folks use it for their backup files:
471 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
473 Finally, the B<-i> switch does not impede execution when no
474 files are given on the command line. In this case, no backup is made
475 (the original file cannot, of course, be determined) and processing
476 proceeds from STDIN to STDOUT as might be expected.
478 =item B<-I>I<directory>
480 Directories specified by B<-I> are prepended to the search path for
481 modules (C<@INC>), and also tells the C preprocessor where to search for
482 include files. The C preprocessor is invoked with B<-P>; by default it
483 searches /usr/include and /usr/lib/perl.
485 =item B<-l>[I<octnum>]
487 enables automatic line-ending processing. It has two separate
488 effects. First, it automatically chomps C<$/> (the input record
489 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
490 (the output record separator) to have the value of I<octnum> so
491 that any print statements will have that separator added back on.
492 If I<octnum> is omitted, sets C<$\> to the current value of
493 C<$/>. For instance, to trim lines to 80 columns:
495 perl -lpe 'substr($_, 80) = ""'
497 Note that the assignment C<$\ = $/> is done when the switch is processed,
498 so the input record separator can be different than the output record
499 separator if the B<-l> switch is followed by a B<-0> switch:
501 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
503 This sets C<$\> to newline and then sets C<$/> to the null character.
505 =item B<-m>[B<->]I<module>
507 =item B<-M>[B<->]I<module>
509 =item B<-M>[B<->]I<'module ...'>
511 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
513 B<-m>I<module> executes C<use> I<module> C<();> before executing your
516 B<-M>I<module> executes C<use> I<module> C<;> before executing your
517 program. You can use quotes to add extra code after the module name,
518 e.g., C<'-Mmodule qw(foo bar)'>.
520 If the first character after the B<-M> or B<-m> is a dash (C<->)
521 then the 'use' is replaced with 'no'.
523 A little builtin syntactic sugar means you can also say
524 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
525 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
526 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
527 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
528 removes the distinction between B<-m> and B<-M>.
532 causes Perl to assume the following loop around your program, which
533 makes it iterate over filename arguments somewhat like B<sed -n> or
538 ... # your program goes here
541 Note that the lines are not printed by default. See B<-p> to have
542 lines printed. If a file named by an argument cannot be opened for
543 some reason, Perl warns you about it and moves on to the next file.
545 Here is an efficient way to delete all files older than a week:
547 find . -mtime +7 -print | perl -nle unlink
549 This is faster than using the B<-exec> switch of B<find> because you don't
550 have to start a process on every filename found. It does suffer from
551 the bug of mishandling newlines in pathnames, which you can fix if
552 you follow the example under B<-0>.
554 C<BEGIN> and C<END> blocks may be used to capture control before or after
555 the implicit program loop, just as in B<awk>.
559 causes Perl to assume the following loop around your program, which
560 makes it iterate over filename arguments somewhat like B<sed>:
565 ... # your program goes here
567 print or die "-p destination: $!\n";
570 If a file named by an argument cannot be opened for some reason, Perl
571 warns you about it, and moves on to the next file. Note that the
572 lines are printed automatically. An error occurring during printing is
573 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
574 overrides a B<-n> switch.
576 C<BEGIN> and C<END> blocks may be used to capture control before or after
577 the implicit loop, just as in B<awk>.
581 B<NOTE: Use of -P is strongly discouraged because of its inherent
582 problems, including poor portability.>
584 This option causes your program to be run through the C preprocessor before
585 compilation by Perl. Because both comments and B<cpp> directives begin
586 with the # character, you should avoid starting comments with any words
587 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
589 If you're considering using C<-P>, you might also want to look at the
590 Filter::cpp module from CPAN.
592 The problems of -P include, but are not limited to:
598 The C<#!> line is stripped, so any switches there don't apply.
602 A C<-P> on a C<#!> line doesn't work.
606 B<All> lines that begin with (whitespace and) a C<#> but
607 do not look like cpp commands, are stripped, including anything
608 inside Perl strings, regular expressions, and here-docs .
612 In some platforms the C preprocessor knows too much: it knows about
613 the C++ -style until-end-of-line comments starting with C<"//">.
614 This will cause problems with common Perl constructs like
618 because after -P this will became illegal code
622 The workaround is to use some other quoting separator than C<"/">,
623 like for example C<"!">:
631 It requires not only a working C preprocessor but also a working
632 F<sed>. If not on UNIX, you are probably out of luck on this.
636 Script line numbers are not preserved.
640 The C<-x> does not work with C<-P>.
646 enables rudimentary switch parsing for switches on the command
647 line after the program name but before any filename arguments (or before
648 an argument of B<-->). This means you can have switches with two leading
649 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
650 corresponding variable in the Perl program. The following program
651 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
652 if it is invoked with B<-xyz=abc>.
655 if ($xyz) { print "$xyz\n" }
657 Do note that B<--help> creates the variable ${-help}, which is not compliant
662 makes Perl use the PATH environment variable to search for the
663 program (unless the name of the program contains directory separators).
665 On some platforms, this also makes Perl append suffixes to the
666 filename while searching for it. For example, on Win32 platforms,
667 the ".bat" and ".cmd" suffixes are appended if a lookup for the
668 original name fails, and if the name does not already end in one
669 of those suffixes. If your Perl was compiled with DEBUGGING turned
670 on, using the -Dp switch to Perl shows how the search progresses.
672 Typically this is used to emulate #! startup on platforms that
673 don't support #!. This example works on many platforms that
674 have a shell compatible with Bourne shell:
677 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
678 if $running_under_some_shell;
680 The system ignores the first line and feeds the program to F</bin/sh>,
681 which proceeds to try to execute the Perl program as a shell script.
682 The shell executes the second line as a normal shell command, and thus
683 starts up the Perl interpreter. On some systems $0 doesn't always
684 contain the full pathname, so the B<-S> tells Perl to search for the
685 program if necessary. After Perl locates the program, it parses the
686 lines and ignores them because the variable $running_under_some_shell
687 is never true. If the program will be interpreted by csh, you will need
688 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
689 embedded spaces (and such) in the argument list. To start up sh rather
690 than csh, some systems may have to replace the #! line with a line
691 containing just a colon, which will be politely ignored by Perl. Other
692 systems can't control that, and need a totally devious construct that
693 will work under any of B<csh>, B<sh>, or Perl, such as the following:
695 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
696 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
697 if $running_under_some_shell;
699 If the filename supplied contains directory separators (i.e., is an
700 absolute or relative pathname), and if that file is not found,
701 platforms that append file extensions will do so and try to look
702 for the file with those extensions added, one by one.
704 On DOS-like platforms, if the program does not contain directory
705 separators, it will first be searched for in the current directory
706 before being searched for on the PATH. On Unix platforms, the
707 program will be searched for strictly on the PATH.
711 Like B<-T>, but taint checks will issue warnings rather than fatal
712 errors. These warnings can be controlled normally with C<no warnings
715 B<NOTE: this is not a substitute for -T.> This is meant only to be
716 used as a temporary development aid while securing legacy code:
717 for real production code and for new secure code written from scratch
718 always use the real B<-T>.
722 forces "taint" checks to be turned on so you can test them. Ordinarily
723 these checks are done only when running setuid or setgid. It's a
724 good idea to turn them on explicitly for programs that run on behalf
725 of someone else whom you might not necessarily trust, such as CGI
726 programs or any internet servers you might write in Perl. See
727 L<perlsec> for details. For security reasons, this option must be
728 seen by Perl quite early; usually this means it must appear early
729 on the command line or in the #! line for systems which support
734 This obsolete switch causes Perl to dump core after compiling your
735 program. You can then in theory take this core dump and turn it
736 into an executable file by using the B<undump> program (not supplied).
737 This speeds startup at the expense of some disk space (which you
738 can minimize by stripping the executable). (Still, a "hello world"
739 executable comes out to about 200K on my machine.) If you want to
740 execute a portion of your program before dumping, use the dump()
741 operator instead. Note: availability of B<undump> is platform
742 specific and may not be available for a specific port of Perl.
744 This switch has been superseded in favor of the new Perl code
745 generator backends to the compiler. See L<B> and L<B::Bytecode>
750 allows Perl to do unsafe operations. Currently the only "unsafe"
751 operations are the unlinking of directories while running as superuser,
752 and running setuid programs with fatal taint checks turned into
753 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
754 be used along with this option to actually I<generate> the
755 taint-check warnings.
759 prints the version and patchlevel of your perl executable.
763 prints summary of the major perl configuration values and the current
768 Prints to STDOUT the value of the named configuration variable.
773 will provide strong clues about what your MANPATH variable should
774 be set to in order to access the Perl documentation.
778 prints warnings about dubious constructs, such as variable names
779 that are mentioned only once and scalar variables that are used
780 before being set, redefined subroutines, references to undefined
781 filehandles or filehandles opened read-only that you are attempting
782 to write on, values used as a number that doesn't look like numbers,
783 using an array as though it were a scalar, if your subroutines
784 recurse more than 100 deep, and innumerable other things.
786 This switch really just enables the internal C<^$W> variable. You
787 can disable or promote into fatal errors specific warnings using
788 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
789 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
790 facility is also available if you want to manipulate entire classes
791 of warnings; see L<warnings> or L<perllexwarn>.
795 Enables all warnings regardless of C<no warnings> or C<$^W>.
800 Disables all warnings regardless of C<use warnings> or C<$^W>.
803 =item B<-x> I<directory>
805 tells Perl that the program is embedded in a larger chunk of unrelated
806 ASCII text, such as in a mail message. Leading garbage will be
807 discarded until the first line that starts with #! and contains the
808 string "perl". Any meaningful switches on that line will be applied.
809 If a directory name is specified, Perl will switch to that directory
810 before running the program. The B<-x> switch controls only the
811 disposal of leading garbage. The program must be terminated with
812 C<__END__> if there is trailing garbage to be ignored (the program
813 can process any or all of the trailing garbage via the DATA filehandle
824 Used if chdir has no argument.
828 Used if chdir has no argument and HOME is not set.
832 Used in executing subprocesses, and in finding the program if B<-S> is
837 A colon-separated list of directories in which to look for Perl library
838 files before looking in the standard library and the current
839 directory. Any architecture-specific directories under the specified
840 locations are automatically included if they exist. If PERL5LIB is not
841 defined, PERLLIB is used.
843 When running taint checks (either because the program was running setuid
844 or setgid, or the B<-T> switch was used), neither variable is used.
845 The program should instead say:
847 use lib "/my/directory";
851 Command-line options (switches). Switches in this variable are taken
852 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
853 switches are allowed. When running taint checks (because the program
854 was running setuid or setgid, or the B<-T> switch was used), this
855 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
856 enabled, and any subsequent options ignored.
860 A space (or colon) separated list of PerlIO layers. If perl is built
861 to use PerlIO system for IO (the default) these layers affect perl's IO.
863 It is conventional to start layer names with a colon e.g. C<:perlio> to
864 emphasise their similarity to variable "attributes". But the code that parses
865 layer specification strings (which is also used to decode the PERLIO
866 environment variable) treats the colon as a separator.
868 The list becomes the default for I<all> perl's IO. Consequently only built-in
869 layers can appear in this list, as external layers (such as :encoding()) need
870 IO in order to load them!. See L<"open pragma"|open> for how to add external
871 encodings as defaults.
873 The layers that it makes sense to include in the PERLIO environment
874 variable are summarised below. For more details see L<PerlIO>.
880 Turns I<off> the C<:utf8> flag for the layer below.
881 Unlikely to be useful in global PERLIO environment variable.
885 A layer that implements DOS/Windows like CRLF line endings.
886 On read converts pairs of CR,LF to a single "\n" newline character.
887 On write converts each "\n" to a CR,LF pair.
888 Based on the C<:perlio> layer.
892 A layer which implements "reading" of files by using C<mmap()> to
893 make (whole) file appear in the process's address space, and then
894 using that as PerlIO's "buffer". This I<may> be faster in certain
895 circumstances for large files, and may result in less physical memory
896 use when multiple processes are reading the same file.
898 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
899 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
900 needs extra house-keeping (to extend the file) which negates any advantage.
902 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
906 A from scratch implementation of buffering for PerlIO. Provides fast
907 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
908 and in general attempts to minimize data copying.
910 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
914 Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
915 It makes the stream pass each byte as-is without any translation.
916 In particular CRLF translation, and/or :utf8 inuited from locale
919 Arranges for all accesses go straight to the lowest buffered layer provided
920 by the configration. That is it strips off any layers above that layer.
922 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
923 referred to as a "discipline") is documented as the inverse of the
924 C<:crlf> layer. That is no longer the case - other layers which would
925 alter binary nature of the stream are also disabled. If you want UNIX
926 line endings on a platform that normally does CRLF translation, but still
927 want UTF-8 or encoding defaults the appropriate thing to do is to add
928 C<:perlio> to PERLIO environment variable.
932 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
933 library calls. The layer provides both buffering and IO.
934 Note that C<:stdio> layer does I<not> do CRLF translation even if that
935 is platforms normal behaviour. You will need a C<:crlf> layer above it
940 Lowest level layer which provides basic PerlIO operations in terms of
941 UNIX/POSIX numeric file descriptor calls
942 C<open(), read(), write(), lseek(), close()>
946 Turns on a flag on the layer below to tell perl that data sent to the
947 stream should be converted to perl internal "utf8" form and that data from the
948 stream should be considered as so encoded. On ASCII based platforms the
949 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
950 May be useful in PERLIO environment variable to make UTF-8 the
951 default. (To turn off that behaviour use C<:bytes> layer.)
955 On Win32 platforms this I<experimental> layer uses native "handle" IO
956 rather than unix-like numeric file descriptor layer. Known to be
957 buggy in this release.
961 On all platforms the default set of layers should give acceptable results.
963 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
964 Configure is setup to prefer "stdio" implementation if system's library
965 provides for fast access to the buffer, otherwise it uses the "unix perlio"
968 On Win32 the default in this release is "unix crlf". Win32's "stdio"
969 has a number of bugs/mis-features for perl IO which are somewhat
970 C compiler vendor/version dependent. Using our own C<crlf> layer as
971 the buffer avoids those issues and makes things more uniform.
972 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
975 This release uses C<unix> as the bottom layer on Win32 and so still uses C
976 compiler's numeric file descriptor routines. There is an experimental native
977 C<win32> layer which is expected to be enhanced and should eventually replace
982 If set to the name of a file or device then certain operations of PerlIO
983 sub-system will be logged to that file (opened as append). Typical uses
986 PERLIO_DEBUG=/dev/tty perl script ...
988 and Win32 approximate equivalent:
996 A colon-separated list of directories in which to look for Perl library
997 files before looking in the standard library and the current directory.
998 If PERL5LIB is defined, PERLLIB is not used.
1002 The command used to load the debugger code. The default is:
1004 BEGIN { require 'perl5db.pl' }
1006 =item PERL5SHELL (specific to the Win32 port)
1008 May be set to an alternative shell that perl must use internally for
1009 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1010 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1011 to be space-separated. Precede any character that needs to be protected
1012 (like a space or backslash) with a backslash.
1014 Note that Perl doesn't use COMSPEC for this purpose because
1015 COMSPEC has a high degree of variability among users, leading to
1016 portability concerns. Besides, perl can use a shell that may not be
1017 fit for interactive use, and setting COMSPEC to such a shell may
1018 interfere with the proper functioning of other programs (which usually
1019 look in COMSPEC to find a shell fit for interactive use).
1021 =item PERL_DEBUG_MSTATS
1023 Relevant only if perl is compiled with the malloc included with the perl
1024 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1025 If set, this causes memory statistics to be dumped after execution. If set
1026 to an integer greater than one, also causes memory statistics to be dumped
1029 =item PERL_DESTRUCT_LEVEL
1031 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1032 this controls the behavior of global destruction of objects and other
1033 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1037 If using the C<encoding> pragma without an explicit encoding name, the
1038 PERL_ENCODING environment variable is consulted for an encoding name.
1040 =item PERL_ROOT (specific to the VMS port)
1042 A translation concealed rooted logical name that contains perl and the
1043 logical device for the @INC path on VMS only. Other logical names that
1044 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1045 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1046 L<perlvms> and in F<README.vms> in the Perl source distribution.
1048 =item SYS$LOGIN (specific to the VMS port)
1050 Used if chdir has no argument and HOME and LOGDIR are not set.
1054 Perl also has environment variables that control how Perl handles data
1055 specific to particular natural languages. See L<perllocale>.
1057 Apart from these, Perl uses no other environment variables, except
1058 to make them available to the program being executed, and to child
1059 processes. However, programs running setuid would do well to execute
1060 the following lines before doing anything else, just to keep people
1063 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1064 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1065 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};