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 Plan9 systems. You might also
170 have to change a single % to a %%.
175 perl -e 'print "Hello world\n"'
178 perl -e "print \"Hello world\n\""
181 print "Hello world\n"
182 (then Run "Myscript" or Shift-Command-R)
185 perl -e "print ""Hello world\n"""
187 The problem is that none of this is reliable: it depends on the
188 command and it is entirely possible neither works. If B<4DOS> were
189 the command shell, this would probably work better:
191 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
193 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
194 when nobody was looking, but just try to find documentation for its
197 Under the Macintosh, it depends which environment you are using. The MacPerl
198 shell, or MPW, is much like Unix shells in its support for several
199 quoting variants, except that it makes free use of the Macintosh's non-ASCII
200 characters as control characters.
202 There is no general solution to all of this. It's just a mess.
204 =head2 Location of Perl
206 It may seem obvious to say, but Perl is useful only when users can
207 easily find it. When possible, it's good for both F</usr/bin/perl>
208 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
209 that can't be done, system administrators are strongly encouraged
210 to put (symlinks to) perl and its accompanying utilities into a
211 directory typically found along a user's PATH, or in some other
212 obvious and convenient place.
214 In this documentation, C<#!/usr/bin/perl> on the first line of the program
215 will stand in for whatever method works on your system. You are
216 advised to use a specific path if you care about a specific version.
218 #!/usr/local/bin/perl5.00554
220 or if you just want to be running at least version, place a statement
221 like this at the top of your program:
225 =head2 Command Switches
227 As with all standard commands, a single-character switch may be
228 clustered with the following switch, if any.
230 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
236 =item B<-0>[I<digits>]
238 specifies the input record separator (C<$/>) as an octal number. If there are
239 no digits, the null character is the separator. Other switches may
240 precede or follow the digits. For example, if you have a version of
241 B<find> which can print filenames terminated by the null character, you
244 find . -name '*.orig' -print0 | perl -n0e unlink
246 The special value 00 will cause Perl to slurp files in paragraph mode.
247 The value 0777 will cause Perl to slurp files whole because there is no
248 legal character with that value.
252 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
253 split command to the @F array is done as the first thing inside the
254 implicit while loop produced by the B<-n> or B<-p>.
256 perl -ane 'print pop(@F), "\n";'
265 An alternate delimiter may be specified using B<-F>.
269 enables Perl to use the native wide character APIs on the target system.
270 The magic variable C<${^WIDE_SYSTEM_CALLS}> reflects the state of
271 this switch. See L<perlvar/"${^WIDE_SYSTEM_CALLS}">.
273 This feature is currently only implemented on the Win32 platform.
277 causes Perl to check the syntax of the program and then exit without
278 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
279 C<use> blocks, because these are considered as occurring outside the
280 execution of your program. C<INIT> and C<END> blocks, however, will
285 runs the program under the Perl debugger. See L<perldebug>.
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 4 l Context (loop) stack processing
314 16 o Method and overloading resolution
315 32 c String/numeric conversions
316 64 P Print profiling info, preprocessor command for -P, source file input state
317 128 m Memory allocation
318 256 f Format processing
319 512 r Regular expression parsing and execution
320 1024 x Syntax tree dump
321 2048 u Tainting checks
322 4096 L Memory leaks (needs -DLEAKTEST when compiling Perl)
323 8192 H Hash dump -- usurps values()
324 16384 X Scratchpad allocation
326 65536 S Thread synchronization
328 262144 R Include reference counts of dumped variables (eg when using -Ds)
329 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
331 All these flags require B<-DDEBUGGING> when you compile the Perl
332 executable (but see L<Devel::Peek>, L<re> which may change this).
333 See the F<INSTALL> file in the Perl source distribution
334 for how to do this. This flag is automatically set if you include B<-g>
335 option when C<Configure> asks you about optimizer/debugger flags.
337 If you're just trying to get a print out of each line of Perl code
338 as it executes, the way that C<sh -x> provides for shell scripts,
339 you can't use Perl's B<-D> switch. Instead do this
341 # If you have "env" utility
342 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
344 # Bourne shell syntax
345 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
348 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
350 See L<perldebug> for details and variations.
352 =item B<-e> I<commandline>
354 may be used to enter one line of program. If B<-e> is given, Perl
355 will not look for a filename in the argument list. Multiple B<-e>
356 commands may be given to build up a multi-line script. Make sure
357 to use semicolons where you would in a normal program.
359 =item B<-F>I<pattern>
361 specifies the pattern to split on if B<-a> is also in effect. The
362 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
363 put in single quotes.
367 prints a summary of the options.
369 =item B<-i>[I<extension>]
371 specifies that files processed by the C<E<lt>E<gt>> construct are to be
372 edited in-place. It does this by renaming the input file, opening the
373 output file by the original name, and selecting that output file as the
374 default for print() statements. The extension, if supplied, is used to
375 modify the name of the old file to make a backup copy, following these
378 If no extension is supplied, no backup is made and the current file is
381 If the extension doesn't contain a C<*>, then it is appended to the
382 end of the current filename as a suffix. If the extension does
383 contain one or more C<*> characters, then each C<*> is replaced
384 with the current filename. In Perl terms, you could think of this
387 ($backup = $extension) =~ s/\*/$file_name/g;
389 This allows you to add a prefix to the backup file, instead of (or in
390 addition to) a suffix:
392 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
394 Or even to place backup copies of the original files into another
395 directory (provided the directory already exists):
397 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
399 These sets of one-liners are equivalent:
401 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
402 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
404 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
405 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
407 From the shell, saying
409 $ perl -p -i.orig -e "s/foo/bar/; ... "
411 is the same as using the program:
413 #!/usr/bin/perl -pi.orig
416 which is equivalent to
419 $extension = '.orig';
421 if ($ARGV ne $oldargv) {
422 if ($extension !~ /\*/) {
423 $backup = $ARGV . $extension;
426 ($backup = $extension) =~ s/\*/$ARGV/g;
428 rename($ARGV, $backup);
429 open(ARGVOUT, ">$ARGV");
436 print; # this prints to original filename
440 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
441 know when the filename has changed. It does, however, use ARGVOUT for
442 the selected filehandle. Note that STDOUT is restored as the default
443 output filehandle after the loop.
445 As shown above, Perl creates the backup file whether or not any output
446 is actually changed. So this is just a fancy way to copy files:
448 $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3...
450 $ perl -p -i '.orig' -e 1 file1 file2 file3...
452 You can use C<eof> without parentheses to locate the end of each input
453 file, in case you want to append to each file, or reset line numbering
454 (see example in L<perlfunc/eof>).
456 If, for a given file, Perl is unable to create the backup file as
457 specified in the extension then it will skip that file and continue on
458 with the next one (if it exists).
460 For a discussion of issues surrounding file permissions and B<-i>,
461 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?>.
463 You cannot use B<-i> to create directories or to strip extensions from
466 Perl does not expand C<~> in filenames, which is good, since some
467 folks use it for their backup files:
469 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
471 Finally, the B<-i> switch does not impede execution when no
472 files are given on the command line. In this case, no backup is made
473 (the original file cannot, of course, be determined) and processing
474 proceeds from STDIN to STDOUT as might be expected.
476 =item B<-I>I<directory>
478 Directories specified by B<-I> are prepended to the search path for
479 modules (C<@INC>), and also tells the C preprocessor where to search for
480 include files. The C preprocessor is invoked with B<-P>; by default it
481 searches /usr/include and /usr/lib/perl.
483 =item B<-l>[I<octnum>]
485 enables automatic line-ending processing. It has two separate
486 effects. First, it automatically chomps C<$/> (the input record
487 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
488 (the output record separator) to have the value of I<octnum> so
489 that any print statements will have that separator added back on.
490 If I<octnum> is omitted, sets C<$\> to the current value of
491 C<$/>. For instance, to trim lines to 80 columns:
493 perl -lpe 'substr($_, 80) = ""'
495 Note that the assignment C<$\ = $/> is done when the switch is processed,
496 so the input record separator can be different than the output record
497 separator if the B<-l> switch is followed by a B<-0> switch:
499 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
501 This sets C<$\> to newline and then sets C<$/> to the null character.
503 =item B<-m>[B<->]I<module>
505 =item B<-M>[B<->]I<module>
507 =item B<-M>[B<->]I<'module ...'>
509 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
511 B<-m>I<module> executes C<use> I<module> C<();> before executing your
514 B<-M>I<module> executes C<use> I<module> C<;> before executing your
515 program. You can use quotes to add extra code after the module name,
516 e.g., C<'-Mmodule qw(foo bar)'>.
518 If the first character after the B<-M> or B<-m> is a dash (C<->)
519 then the 'use' is replaced with 'no'.
521 A little builtin syntactic sugar means you can also say
522 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
523 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
524 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
525 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
526 removes the distinction between B<-m> and B<-M>.
530 causes Perl to assume the following loop around your program, which
531 makes it iterate over filename arguments somewhat like B<sed -n> or
536 ... # your program goes here
539 Note that the lines are not printed by default. See B<-p> to have
540 lines printed. If a file named by an argument cannot be opened for
541 some reason, Perl warns you about it and moves on to the next file.
543 Here is an efficient way to delete all files older than a week:
545 find . -mtime +7 -print | perl -nle unlink
547 This is faster than using the B<-exec> switch of B<find> because you don't
548 have to start a process on every filename found. It does suffer from
549 the bug of mishandling newlines in pathnames, which you can fix if
550 you follow the example under B<-0>.
552 C<BEGIN> and C<END> blocks may be used to capture control before or after
553 the implicit program loop, just as in B<awk>.
557 causes Perl to assume the following loop around your program, which
558 makes it iterate over filename arguments somewhat like B<sed>:
563 ... # your program goes here
565 print or die "-p destination: $!\n";
568 If a file named by an argument cannot be opened for some reason, Perl
569 warns you about it, and moves on to the next file. Note that the
570 lines are printed automatically. An error occurring during printing is
571 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
572 overrides a B<-n> switch.
574 C<BEGIN> and C<END> blocks may be used to capture control before or after
575 the implicit loop, just as in B<awk>.
579 B<NOTE: Use of -P is strongly discouraged because of its inherent
580 problems, including poor portability.>
582 This option causes your program to be run through the C preprocessor before
583 compilation by Perl. Because both comments and B<cpp> directives begin
584 with the # character, you should avoid starting comments with any words
585 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
587 If you're considering using C<-P>, you might also want to look at the
588 Filter::cpp module from CPAN.
590 The problems of -P include, but are not limited to:
596 The C<#!> line is stripped, so any switches there don't apply.
600 A C<-P> on a C<#!> line doesn't work.
604 B<All> lines that begin with (whitespace and) a C<#> but
605 do not look like cpp commands, are stripped, including anything
606 inside Perl strings, regular expressions, and here-docs .
610 In some platforms the C preprocessor knows too much: it knows about
611 the C++ -style until-end-of-line comments starting with C<"//">.
612 This will cause problems with common Perl constructs like
616 because after -P this will became illegal code
620 The workaround is to use some other quoting separator than C<"/">,
621 like for example C<"!">:
629 It requires not only a working C preprocessor but also a working
630 F<sed>. If not on UNIX, you are probably out of luck on this.
634 Script line numbers are not preserved.
638 The C<-x> does not work with C<-P>.
644 enables rudimentary switch parsing for switches on the command
645 line after the program name but before any filename arguments (or before
646 an argument of B<-->). This means you can have switches with two leading
647 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
648 corresponding variable in the Perl program. The following program
649 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
650 if it is invoked with B<-xyz=abc>.
653 if ($xyz) { print "$xyz\n" }
655 Do note that B<--help> creates the variable ${-help}, which is not compliant
660 makes Perl use the PATH environment variable to search for the
661 program (unless the name of the program contains directory separators).
663 On some platforms, this also makes Perl append suffixes to the
664 filename while searching for it. For example, on Win32 platforms,
665 the ".bat" and ".cmd" suffixes are appended if a lookup for the
666 original name fails, and if the name does not already end in one
667 of those suffixes. If your Perl was compiled with DEBUGGING turned
668 on, using the -Dp switch to Perl shows how the search progresses.
670 Typically this is used to emulate #! startup on platforms that
671 don't support #!. This example works on many platforms that
672 have a shell compatible with Bourne shell:
675 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
676 if $running_under_some_shell;
678 The system ignores the first line and feeds the program to F</bin/sh>,
679 which proceeds to try to execute the Perl program as a shell script.
680 The shell executes the second line as a normal shell command, and thus
681 starts up the Perl interpreter. On some systems $0 doesn't always
682 contain the full pathname, so the B<-S> tells Perl to search for the
683 program if necessary. After Perl locates the program, it parses the
684 lines and ignores them because the variable $running_under_some_shell
685 is never true. If the program will be interpreted by csh, you will need
686 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
687 embedded spaces (and such) in the argument list. To start up sh rather
688 than csh, some systems may have to replace the #! line with a line
689 containing just a colon, which will be politely ignored by Perl. Other
690 systems can't control that, and need a totally devious construct that
691 will work under any of B<csh>, B<sh>, or Perl, such as the following:
693 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
694 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
695 if $running_under_some_shell;
697 If the filename supplied contains directory separators (i.e., is an
698 absolute or relative pathname), and if that file is not found,
699 platforms that append file extensions will do so and try to look
700 for the file with those extensions added, one by one.
702 On DOS-like platforms, if the program does not contain directory
703 separators, it will first be searched for in the current directory
704 before being searched for on the PATH. On Unix platforms, the
705 program will be searched for strictly on the PATH.
709 Like B<-T>, but taint checks will issue warnings rather than fatal
710 errors. These warnings can be controlled normally with C<no warnings
713 B<NOTE: this is not a substitute for -T.> This is meant only to be
714 used as a temporary development aid while securing legacy code:
715 for real production code and for new secure code written from scratch
716 always use the real B<-T>.
720 forces "taint" checks to be turned on so you can test them. Ordinarily
721 these checks are done only when running setuid or setgid. It's a
722 good idea to turn them on explicitly for programs that run on behalf
723 of someone else whom you might not necessarily trust, such as CGI
724 programs or any internet servers you might write in Perl. See
725 L<perlsec> for details. For security reasons, this option must be
726 seen by Perl quite early; usually this means it must appear early
727 on the command line or in the #! line for systems which support
732 This obsolete switch causes Perl to dump core after compiling your
733 program. You can then in theory take this core dump and turn it
734 into an executable file by using the B<undump> program (not supplied).
735 This speeds startup at the expense of some disk space (which you
736 can minimize by stripping the executable). (Still, a "hello world"
737 executable comes out to about 200K on my machine.) If you want to
738 execute a portion of your program before dumping, use the dump()
739 operator instead. Note: availability of B<undump> is platform
740 specific and may not be available for a specific port of Perl.
742 This switch has been superseded in favor of the new Perl code
743 generator backends to the compiler. See L<B> and L<B::Bytecode>
748 allows Perl to do unsafe operations. Currently the only "unsafe"
749 operations are the unlinking of directories while running as superuser,
750 and running setuid programs with fatal taint checks turned into
751 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
752 be used along with this option to actually I<generate> the
753 taint-check warnings.
757 prints the version and patchlevel of your perl executable.
761 prints summary of the major perl configuration values and the current
766 Prints to STDOUT the value of the named configuration variable.
771 will provide strong clues about what your MANPATH variable should
772 be set to in order to access the Perl documentation.
776 prints warnings about dubious constructs, such as variable names
777 that are mentioned only once and scalar variables that are used
778 before being set, redefined subroutines, references to undefined
779 filehandles or filehandles opened read-only that you are attempting
780 to write on, values used as a number that doesn't look like numbers,
781 using an array as though it were a scalar, if your subroutines
782 recurse more than 100 deep, and innumerable other things.
784 This switch really just enables the internal C<^$W> variable. You
785 can disable or promote into fatal errors specific warnings using
786 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
787 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
788 facility is also available if you want to manipulate entire classes
789 of warnings; see L<warnings> or L<perllexwarn>.
793 Enables all warnings regardless of C<no warnings> or C<$^W>.
798 Disables all warnings regardless of C<use warnings> or C<$^W>.
801 =item B<-x> I<directory>
803 tells Perl that the program is embedded in a larger chunk of unrelated
804 ASCII text, such as in a mail message. Leading garbage will be
805 discarded until the first line that starts with #! and contains the
806 string "perl". Any meaningful switches on that line will be applied.
807 If a directory name is specified, Perl will switch to that directory
808 before running the program. The B<-x> switch controls only the
809 disposal of leading garbage. The program must be terminated with
810 C<__END__> if there is trailing garbage to be ignored (the program
811 can process any or all of the trailing garbage via the DATA filehandle
822 Used if chdir has no argument.
826 Used if chdir has no argument and HOME is not set.
830 Used in executing subprocesses, and in finding the program if B<-S> is
835 A colon-separated list of directories in which to look for Perl library
836 files before looking in the standard library and the current
837 directory. Any architecture-specific directories under the specified
838 locations are automatically included if they exist. If PERL5LIB is not
839 defined, PERLLIB is used.
841 When running taint checks (either because the program was running setuid
842 or setgid, or the B<-T> switch was used), neither variable is used.
843 The program should instead say:
845 use lib "/my/directory";
849 Command-line options (switches). Switches in this variable are taken
850 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
851 switches are allowed. When running taint checks (because the program
852 was running setuid or setgid, or the B<-T> switch was used), this
853 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
854 enabled, and any subsequent options ignored.
858 A space (or colon) separated list of PerlIO layers. If perl is built
859 to use PerlIO system for IO (the default) these layers effect perl's IO.
861 It is conventional to start layer names with a colon e.g. C<:perlio> to
862 emphasise their similarity to variable "attributes". But the code that parses
863 layer specification strings (which is also used to decode the PERLIO
864 environment variable) treats the colon as a separator.
866 The list becomes the default for I<all> perl's IO. Consequently only built-in
867 layers can appear in this list, as external layers (such as :encoding()) need
868 IO in order to load them!. See L<"open pragma"|open> for how to add external
869 encodings as defaults.
871 The layers that it makes sense to include in the PERLIO environment
872 variable are summarised below. For more details see L<PerlIO>.
878 Turns I<off> the C<:utf8> flag for the layer below.
879 Unlikely to be useful in global PERLIO environment variable.
883 A layer that implements DOS/Windows like CRLF line endings.
884 On read converts pairs of CR,LF to a single "\n" newline character.
885 On write converts each "\n" to a CR,LF pair.
886 Based on the C<:perlio> layer.
890 A layer which implements "reading" of files by using C<mmap()> to
891 make (whole) file appear in the process's address space, and then
892 using that as PerlIO's "buffer". This I<may> be faster in certain
893 circumstances for large files, and may result in less physical memory
894 use when multiple processes are reading the same file.
896 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
897 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
898 needs extra house-keeping (to extend the file) which negates any advantage.
900 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
904 A from scratch implementation of buffering for PerlIO. Provides fast
905 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
906 and in general attempts to minimize data copying.
908 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
912 Arranges for all accesses go straight to the lowest level layer provided
913 by the configration. That is it strips off any layers above that layer.
914 (The intent - unless layers are then pushed on top again -
915 is to make perl's C<read> behave like C<sysread>.)
917 Not really useful in PERLIO environment variable, instead just use C<:unix>
920 In perl5.6 and some books the C<:raw> layer (also called a discipline) is
921 documented as the inverse of the C<:crlf> layer. That is not really the case.
922 If you want UNIX line endings on a platform that normaly does CRLF translation
923 the appropriate thing to do is to add C<:perlio> to PERLIO environment
928 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
929 library calls. The layer provides both buffering and IO.
930 Note that C<:stdio> layer does I<not> do CRLF translation even if that
931 is platforms normal behaviour. You will need a C<:crlf> layer above it
936 Lowest level layer which provides basic PerlIO operations in terms of
937 UNIX/POSIX numeric file descriptor calls
938 C<open(), read(), write(), lseek(), close()>
942 Turns on a flag on the layer below to tell perl that data sent to the
943 stream should be converted to perl internal "utf8" form and that data from the
944 stream should be considered as so encoded. On ASCII based platforms the
945 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
946 May be useful in PERLIO environment variable to make UTF-8 the
947 default. (To turn off that behaviour use C<:bytes> layer.)
951 On Win32 platfroms this I<experimental> layer uses native "handle" IO
952 rather than unix-like numeric file descriptor layer. Known to be
953 buggy in this release.
957 On all platforms the default set of layers should give acceptable results.
959 For UNIX platfroms that will equivalent of "unix perlio" or "stdio".
960 Configure is setup to prefer "stdio" implementation if system's library
961 provides for fast access to the buffer, otherwise it uses the "unix perlio"
964 On Win32 the default in this release is "unix crlf". Win32's "stdio"
965 has a number of bugs/mis-features for perl IO which are somewhat
966 C compiler vendor/version dependent. Using our own C<crlf> layer as
967 the buffer avoids those issues and makes things more uniform.
968 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
971 This release uses C<unix> as the bottom layer on Win32 and so still uses C
972 compiler's numeric file descriptor routines. There is an experimental native
973 C<win32> layer which is expected to be enhanced and should eventually replace
978 If set to the name of a file or device then certain operations of PerlIO
979 sub-system will be logged to that file (opened as append). Typical uses
982 PERLIO_DEBUG=/dev/tty perl script ...
984 and Win32 approximate equivalent:
992 A colon-separated list of directories in which to look for Perl library
993 files before looking in the standard library and the current directory.
994 If PERL5LIB is defined, PERLLIB is not used.
998 The command used to load the debugger code. The default is:
1000 BEGIN { require 'perl5db.pl' }
1002 =item PERL5SHELL (specific to the Win32 port)
1004 May be set to an alternative shell that perl must use internally for
1005 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1006 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1007 to be space-separated. Precede any character that needs to be protected
1008 (like a space or backslash) with a backslash.
1010 Note that Perl doesn't use COMSPEC for this purpose because
1011 COMSPEC has a high degree of variability among users, leading to
1012 portability concerns. Besides, perl can use a shell that may not be
1013 fit for interactive use, and setting COMSPEC to such a shell may
1014 interfere with the proper functioning of other programs (which usually
1015 look in COMSPEC to find a shell fit for interactive use).
1017 =item PERL_DEBUG_MSTATS
1019 Relevant only if perl is compiled with the malloc included with the perl
1020 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1021 If set, this causes memory statistics to be dumped after execution. If set
1022 to an integer greater than one, also causes memory statistics to be dumped
1025 =item PERL_DESTRUCT_LEVEL
1027 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1028 this controls the behavior of global destruction of objects and other
1029 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1033 If using the C<encoding> pragma without an explicit encoding name, the
1034 PERL_ENCODING environment variable is consulted for an encoding name.
1036 =item PERL_ROOT (specific to the VMS port)
1038 A translation concealed rooted logical name that contains perl and the
1039 logical device for the @INC path on VMS only. Other logical names that
1040 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1041 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1042 L<perlvms> and in F<README.vms> in the Perl source distribution.
1044 =item SYS$LOGIN (specific to the VMS port)
1046 Used if chdir has no argument and HOME and LOGDIR are not set.
1050 Perl also has environment variables that control how Perl handles data
1051 specific to particular natural languages. See L<perllocale>.
1053 Apart from these, Perl uses no other environment variables, except
1054 to make them available to the program being executed, and to child
1055 processes. However, programs running setuid would do well to execute
1056 the following lines before doing anything else, just to keep people
1059 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1060 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1061 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};