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 (Obsolete, previously used for LEAKTEST)
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
332 2097152 C Copy On Write
334 All these flags require B<-DDEBUGGING> when you compile the Perl
335 executable (but see L<Devel::Peek>, L<re> which may change this).
336 See the F<INSTALL> file in the Perl source distribution
337 for how to do this. This flag is automatically set if you include B<-g>
338 option when C<Configure> asks you about optimizer/debugger flags.
340 If you're just trying to get a print out of each line of Perl code
341 as it executes, the way that C<sh -x> provides for shell scripts,
342 you can't use Perl's B<-D> switch. Instead do this
344 # If you have "env" utility
345 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
347 # Bourne shell syntax
348 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
351 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
353 See L<perldebug> for details and variations.
355 =item B<-e> I<commandline>
357 may be used to enter one line of program. If B<-e> is given, Perl
358 will not look for a filename in the argument list. Multiple B<-e>
359 commands may be given to build up a multi-line script. Make sure
360 to use semicolons where you would in a normal program.
362 =item B<-F>I<pattern>
364 specifies the pattern to split on if B<-a> is also in effect. The
365 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
366 put in single quotes.
370 prints a summary of the options.
372 =item B<-i>[I<extension>]
374 specifies that files processed by the C<E<lt>E<gt>> construct are to be
375 edited in-place. It does this by renaming the input file, opening the
376 output file by the original name, and selecting that output file as the
377 default for print() statements. The extension, if supplied, is used to
378 modify the name of the old file to make a backup copy, following these
381 If no extension is supplied, no backup is made and the current file is
384 If the extension doesn't contain a C<*>, then it is appended to the
385 end of the current filename as a suffix. If the extension does
386 contain one or more C<*> characters, then each C<*> is replaced
387 with the current filename. In Perl terms, you could think of this
390 ($backup = $extension) =~ s/\*/$file_name/g;
392 This allows you to add a prefix to the backup file, instead of (or in
393 addition to) a suffix:
395 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
397 Or even to place backup copies of the original files into another
398 directory (provided the directory already exists):
400 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
402 These sets of one-liners are equivalent:
404 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
405 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
407 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
408 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
410 From the shell, saying
412 $ perl -p -i.orig -e "s/foo/bar/; ... "
414 is the same as using the program:
416 #!/usr/bin/perl -pi.orig
419 which is equivalent to
422 $extension = '.orig';
424 if ($ARGV ne $oldargv) {
425 if ($extension !~ /\*/) {
426 $backup = $ARGV . $extension;
429 ($backup = $extension) =~ s/\*/$ARGV/g;
431 rename($ARGV, $backup);
432 open(ARGVOUT, ">$ARGV");
439 print; # this prints to original filename
443 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
444 know when the filename has changed. It does, however, use ARGVOUT for
445 the selected filehandle. Note that STDOUT is restored as the default
446 output filehandle after the loop.
448 As shown above, Perl creates the backup file whether or not any output
449 is actually changed. So this is just a fancy way to copy files:
451 $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3...
453 $ perl -p -i '.orig' -e 1 file1 file2 file3...
455 You can use C<eof> without parentheses to locate the end of each input
456 file, in case you want to append to each file, or reset line numbering
457 (see example in L<perlfunc/eof>).
459 If, for a given file, Perl is unable to create the backup file as
460 specified in the extension then it will skip that file and continue on
461 with the next one (if it exists).
463 For a discussion of issues surrounding file permissions and B<-i>,
464 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?>.
466 You cannot use B<-i> to create directories or to strip extensions from
469 Perl does not expand C<~> in filenames, which is good, since some
470 folks use it for their backup files:
472 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
474 Finally, the B<-i> switch does not impede execution when no
475 files are given on the command line. In this case, no backup is made
476 (the original file cannot, of course, be determined) and processing
477 proceeds from STDIN to STDOUT as might be expected.
479 =item B<-I>I<directory>
481 Directories specified by B<-I> are prepended to the search path for
482 modules (C<@INC>), and also tells the C preprocessor where to search for
483 include files. The C preprocessor is invoked with B<-P>; by default it
484 searches /usr/include and /usr/lib/perl.
486 =item B<-l>[I<octnum>]
488 enables automatic line-ending processing. It has two separate
489 effects. First, it automatically chomps C<$/> (the input record
490 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
491 (the output record separator) to have the value of I<octnum> so
492 that any print statements will have that separator added back on.
493 If I<octnum> is omitted, sets C<$\> to the current value of
494 C<$/>. For instance, to trim lines to 80 columns:
496 perl -lpe 'substr($_, 80) = ""'
498 Note that the assignment C<$\ = $/> is done when the switch is processed,
499 so the input record separator can be different than the output record
500 separator if the B<-l> switch is followed by a B<-0> switch:
502 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
504 This sets C<$\> to newline and then sets C<$/> to the null character.
506 =item B<-m>[B<->]I<module>
508 =item B<-M>[B<->]I<module>
510 =item B<-M>[B<->]I<'module ...'>
512 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
514 B<-m>I<module> executes C<use> I<module> C<();> before executing your
517 B<-M>I<module> executes C<use> I<module> C<;> before executing your
518 program. You can use quotes to add extra code after the module name,
519 e.g., C<'-Mmodule qw(foo bar)'>.
521 If the first character after the B<-M> or B<-m> is a dash (C<->)
522 then the 'use' is replaced with 'no'.
524 A little builtin syntactic sugar means you can also say
525 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
526 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
527 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
528 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
529 removes the distinction between B<-m> and B<-M>.
533 causes Perl to assume the following loop around your program, which
534 makes it iterate over filename arguments somewhat like B<sed -n> or
539 ... # your program goes here
542 Note that the lines are not printed by default. See B<-p> to have
543 lines printed. If a file named by an argument cannot be opened for
544 some reason, Perl warns you about it and moves on to the next file.
546 Here is an efficient way to delete all files older than a week:
548 find . -mtime +7 -print | perl -nle unlink
550 This is faster than using the B<-exec> switch of B<find> because you don't
551 have to start a process on every filename found. It does suffer from
552 the bug of mishandling newlines in pathnames, which you can fix if
553 you follow the example under B<-0>.
555 C<BEGIN> and C<END> blocks may be used to capture control before or after
556 the implicit program loop, just as in B<awk>.
560 causes Perl to assume the following loop around your program, which
561 makes it iterate over filename arguments somewhat like B<sed>:
566 ... # your program goes here
568 print or die "-p destination: $!\n";
571 If a file named by an argument cannot be opened for some reason, Perl
572 warns you about it, and moves on to the next file. Note that the
573 lines are printed automatically. An error occurring during printing is
574 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
575 overrides a B<-n> switch.
577 C<BEGIN> and C<END> blocks may be used to capture control before or after
578 the implicit loop, just as in B<awk>.
582 B<NOTE: Use of -P is strongly discouraged because of its inherent
583 problems, including poor portability.>
585 This option causes your program to be run through the C preprocessor before
586 compilation by Perl. Because both comments and B<cpp> directives begin
587 with the # character, you should avoid starting comments with any words
588 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
590 If you're considering using C<-P>, you might also want to look at the
591 Filter::cpp module from CPAN.
593 The problems of -P include, but are not limited to:
599 The C<#!> line is stripped, so any switches there don't apply.
603 A C<-P> on a C<#!> line doesn't work.
607 B<All> lines that begin with (whitespace and) a C<#> but
608 do not look like cpp commands, are stripped, including anything
609 inside Perl strings, regular expressions, and here-docs .
613 In some platforms the C preprocessor knows too much: it knows about
614 the C++ -style until-end-of-line comments starting with C<"//">.
615 This will cause problems with common Perl constructs like
619 because after -P this will became illegal code
623 The workaround is to use some other quoting separator than C<"/">,
624 like for example C<"!">:
632 It requires not only a working C preprocessor but also a working
633 F<sed>. If not on UNIX, you are probably out of luck on this.
637 Script line numbers are not preserved.
641 The C<-x> does not work with C<-P>.
647 enables rudimentary switch parsing for switches on the command
648 line after the program name but before any filename arguments (or before
649 an argument of B<-->). This means you can have switches with two leading
650 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
651 corresponding variable in the Perl program. The following program
652 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
653 if it is invoked with B<-xyz=abc>.
656 if ($xyz) { print "$xyz\n" }
658 Do note that B<--help> creates the variable ${-help}, which is not compliant
663 makes Perl use the PATH environment variable to search for the
664 program (unless the name of the program contains directory separators).
666 On some platforms, this also makes Perl append suffixes to the
667 filename while searching for it. For example, on Win32 platforms,
668 the ".bat" and ".cmd" suffixes are appended if a lookup for the
669 original name fails, and if the name does not already end in one
670 of those suffixes. If your Perl was compiled with DEBUGGING turned
671 on, using the -Dp switch to Perl shows how the search progresses.
673 Typically this is used to emulate #! startup on platforms that
674 don't support #!. This example works on many platforms that
675 have a shell compatible with Bourne shell:
678 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
679 if $running_under_some_shell;
681 The system ignores the first line and feeds the program to F</bin/sh>,
682 which proceeds to try to execute the Perl program as a shell script.
683 The shell executes the second line as a normal shell command, and thus
684 starts up the Perl interpreter. On some systems $0 doesn't always
685 contain the full pathname, so the B<-S> tells Perl to search for the
686 program if necessary. After Perl locates the program, it parses the
687 lines and ignores them because the variable $running_under_some_shell
688 is never true. If the program will be interpreted by csh, you will need
689 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
690 embedded spaces (and such) in the argument list. To start up sh rather
691 than csh, some systems may have to replace the #! line with a line
692 containing just a colon, which will be politely ignored by Perl. Other
693 systems can't control that, and need a totally devious construct that
694 will work under any of B<csh>, B<sh>, or Perl, such as the following:
696 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
697 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
698 if $running_under_some_shell;
700 If the filename supplied contains directory separators (i.e., is an
701 absolute or relative pathname), and if that file is not found,
702 platforms that append file extensions will do so and try to look
703 for the file with those extensions added, one by one.
705 On DOS-like platforms, if the program does not contain directory
706 separators, it will first be searched for in the current directory
707 before being searched for on the PATH. On Unix platforms, the
708 program will be searched for strictly on the PATH.
712 Like B<-T>, but taint checks will issue warnings rather than fatal
713 errors. These warnings can be controlled normally with C<no warnings
716 B<NOTE: this is not a substitute for -T.> This is meant only to be
717 used as a temporary development aid while securing legacy code:
718 for real production code and for new secure code written from scratch
719 always use the real B<-T>.
723 forces "taint" checks to be turned on so you can test them. Ordinarily
724 these checks are done only when running setuid or setgid. It's a
725 good idea to turn them on explicitly for programs that run on behalf
726 of someone else whom you might not necessarily trust, such as CGI
727 programs or any internet servers you might write in Perl. See
728 L<perlsec> for details. For security reasons, this option must be
729 seen by Perl quite early; usually this means it must appear early
730 on the command line or in the #! line for systems which support
735 This obsolete switch causes Perl to dump core after compiling your
736 program. You can then in theory take this core dump and turn it
737 into an executable file by using the B<undump> program (not supplied).
738 This speeds startup at the expense of some disk space (which you
739 can minimize by stripping the executable). (Still, a "hello world"
740 executable comes out to about 200K on my machine.) If you want to
741 execute a portion of your program before dumping, use the dump()
742 operator instead. Note: availability of B<undump> is platform
743 specific and may not be available for a specific port of Perl.
745 This switch has been superseded in favor of the new Perl code
746 generator backends to the compiler. See L<B> and L<B::Bytecode>
751 allows Perl to do unsafe operations. Currently the only "unsafe"
752 operations are the unlinking of directories while running as superuser,
753 and running setuid programs with fatal taint checks turned into
754 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
755 be used along with this option to actually I<generate> the
756 taint-check warnings.
760 prints the version and patchlevel of your perl executable.
764 prints summary of the major perl configuration values and the current
769 Prints to STDOUT the value of the named configuration variable.
774 will provide strong clues about what your MANPATH variable should
775 be set to in order to access the Perl documentation.
779 prints warnings about dubious constructs, such as variable names
780 that are mentioned only once and scalar variables that are used
781 before being set, redefined subroutines, references to undefined
782 filehandles or filehandles opened read-only that you are attempting
783 to write on, values used as a number that doesn't look like numbers,
784 using an array as though it were a scalar, if your subroutines
785 recurse more than 100 deep, and innumerable other things.
787 This switch really just enables the internal C<^$W> variable. You
788 can disable or promote into fatal errors specific warnings using
789 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
790 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
791 facility is also available if you want to manipulate entire classes
792 of warnings; see L<warnings> or L<perllexwarn>.
796 Enables all warnings regardless of C<no warnings> or C<$^W>.
801 Disables all warnings regardless of C<use warnings> or C<$^W>.
804 =item B<-x> I<directory>
806 tells Perl that the program is embedded in a larger chunk of unrelated
807 ASCII text, such as in a mail message. Leading garbage will be
808 discarded until the first line that starts with #! and contains the
809 string "perl". Any meaningful switches on that line will be applied.
810 If a directory name is specified, Perl will switch to that directory
811 before running the program. The B<-x> switch controls only the
812 disposal of leading garbage. The program must be terminated with
813 C<__END__> if there is trailing garbage to be ignored (the program
814 can process any or all of the trailing garbage via the DATA filehandle
825 Used if chdir has no argument.
829 Used if chdir has no argument and HOME is not set.
833 Used in executing subprocesses, and in finding the program if B<-S> is
838 A colon-separated list of directories in which to look for Perl library
839 files before looking in the standard library and the current
840 directory. Any architecture-specific directories under the specified
841 locations are automatically included if they exist. If PERL5LIB is not
842 defined, PERLLIB is used.
844 When running taint checks (either because the program was running setuid
845 or setgid, or the B<-T> switch was used), neither variable is used.
846 The program should instead say:
848 use lib "/my/directory";
852 Command-line options (switches). Switches in this variable are taken
853 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
854 switches are allowed. When running taint checks (because the program
855 was running setuid or setgid, or the B<-T> switch was used), this
856 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
857 enabled, and any subsequent options ignored.
861 A space (or colon) separated list of PerlIO layers. If perl is built
862 to use PerlIO system for IO (the default) these layers effect perl's IO.
864 It is conventional to start layer names with a colon e.g. C<:perlio> to
865 emphasise their similarity to variable "attributes". But the code that parses
866 layer specification strings (which is also used to decode the PERLIO
867 environment variable) treats the colon as a separator.
869 The list becomes the default for I<all> perl's IO. Consequently only built-in
870 layers can appear in this list, as external layers (such as :encoding()) need
871 IO in order to load them!. See L<"open pragma"|open> for how to add external
872 encodings as defaults.
874 The layers that it makes sense to include in the PERLIO environment
875 variable are summarised below. For more details see L<PerlIO>.
881 Turns I<off> the C<:utf8> flag for the layer below.
882 Unlikely to be useful in global PERLIO environment variable.
886 A layer that implements DOS/Windows like CRLF line endings.
887 On read converts pairs of CR,LF to a single "\n" newline character.
888 On write converts each "\n" to a CR,LF pair.
889 Based on the C<:perlio> layer.
893 A layer which implements "reading" of files by using C<mmap()> to
894 make (whole) file appear in the process's address space, and then
895 using that as PerlIO's "buffer". This I<may> be faster in certain
896 circumstances for large files, and may result in less physical memory
897 use when multiple processes are reading the same file.
899 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
900 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
901 needs extra house-keeping (to extend the file) which negates any advantage.
903 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
907 A from scratch implementation of buffering for PerlIO. Provides fast
908 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
909 and in general attempts to minimize data copying.
911 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
915 Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
916 It makes the stream pass each byte as-is without any translation.
917 In particular CRLF translation, and/or :utf8 inuited from locale
920 Arranges for all accesses go straight to the lowest buffered layer provided
921 by the configration. That is it strips off any layers above that layer.
923 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
924 referred to as a "discipline") is documented as the inverse of the
925 C<:crlf> layer. That is no longer the case - other layers which would
926 alter binary nature of the stream are also disabled. If you want UNIX
927 line endings on a platform that normally does CRLF translation, but still
928 want UTF-8 or encoding defaults the appropriate thing to do is to add
929 C<:perlio> to PERLIO environment variable.
933 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
934 library calls. The layer provides both buffering and IO.
935 Note that C<:stdio> layer does I<not> do CRLF translation even if that
936 is platforms normal behaviour. You will need a C<:crlf> layer above it
941 Lowest level layer which provides basic PerlIO operations in terms of
942 UNIX/POSIX numeric file descriptor calls
943 C<open(), read(), write(), lseek(), close()>
947 Turns on a flag on the layer below to tell perl that data sent to the
948 stream should be converted to perl internal "utf8" form and that data from the
949 stream should be considered as so encoded. On ASCII based platforms the
950 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
951 May be useful in PERLIO environment variable to make UTF-8 the
952 default. (To turn off that behaviour use C<:bytes> layer.)
956 On Win32 platforms this I<experimental> layer uses native "handle" IO
957 rather than unix-like numeric file descriptor layer. Known to be
958 buggy in this release.
962 On all platforms the default set of layers should give acceptable results.
964 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
965 Configure is setup to prefer "stdio" implementation if system's library
966 provides for fast access to the buffer, otherwise it uses the "unix perlio"
969 On Win32 the default in this release is "unix crlf". Win32's "stdio"
970 has a number of bugs/mis-features for perl IO which are somewhat
971 C compiler vendor/version dependent. Using our own C<crlf> layer as
972 the buffer avoids those issues and makes things more uniform.
973 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
976 This release uses C<unix> as the bottom layer on Win32 and so still uses C
977 compiler's numeric file descriptor routines. There is an experimental native
978 C<win32> layer which is expected to be enhanced and should eventually replace
983 If set to the name of a file or device then certain operations of PerlIO
984 sub-system will be logged to that file (opened as append). Typical uses
987 PERLIO_DEBUG=/dev/tty perl script ...
989 and Win32 approximate equivalent:
997 A colon-separated list of directories in which to look for Perl library
998 files before looking in the standard library and the current directory.
999 If PERL5LIB is defined, PERLLIB is not used.
1003 The command used to load the debugger code. The default is:
1005 BEGIN { require 'perl5db.pl' }
1007 =item PERL5SHELL (specific to the Win32 port)
1009 May be set to an alternative shell that perl must use internally for
1010 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1011 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1012 to be space-separated. Precede any character that needs to be protected
1013 (like a space or backslash) with a backslash.
1015 Note that Perl doesn't use COMSPEC for this purpose because
1016 COMSPEC has a high degree of variability among users, leading to
1017 portability concerns. Besides, perl can use a shell that may not be
1018 fit for interactive use, and setting COMSPEC to such a shell may
1019 interfere with the proper functioning of other programs (which usually
1020 look in COMSPEC to find a shell fit for interactive use).
1022 =item PERL_DEBUG_MSTATS
1024 Relevant only if perl is compiled with the malloc included with the perl
1025 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1026 If set, this causes memory statistics to be dumped after execution. If set
1027 to an integer greater than one, also causes memory statistics to be dumped
1030 =item PERL_DESTRUCT_LEVEL
1032 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1033 this controls the behavior of global destruction of objects and other
1034 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1038 If using the C<encoding> pragma without an explicit encoding name, the
1039 PERL_ENCODING environment variable is consulted for an encoding name.
1041 =item PERL_ROOT (specific to the VMS port)
1043 A translation concealed rooted logical name that contains perl and the
1044 logical device for the @INC path on VMS only. Other logical names that
1045 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1046 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1047 L<perlvms> and in F<README.vms> in the Perl source distribution.
1049 =item SYS$LOGIN (specific to the VMS port)
1051 Used if chdir has no argument and HOME and LOGDIR are not set.
1055 Perl also has environment variables that control how Perl handles data
1056 specific to particular natural languages. See L<perllocale>.
1058 Apart from these, Perl uses no other environment variables, except
1059 to make them available to the program being executed, and to child
1060 processes. However, programs running setuid would do well to execute
1061 the following lines before doing anything else, just to keep people
1064 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1065 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1066 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};