3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTtuUWX> ]>
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> ]...>
17 S<[ B<-C[:I<boolean>]> ]>
21 The normal way to run a Perl program is by making it directly
22 executable, or else by passing the name of the source file as an
23 argument on the command line. (An interactive Perl environment
24 is also possible--see L<perldebug> for details on how to do that.)
25 Upon startup, Perl looks for your program in one of the following
32 Specified line by line via B<-e> switches on the command line.
36 Contained in the file specified by the first filename on the command line.
37 (Note that systems supporting the #! notation invoke interpreters this
38 way. See L<Location of Perl>.)
42 Passed in implicitly via standard input. This works only if there are
43 no filename arguments--to pass arguments to a STDIN-read program you
44 must explicitly specify a "-" for the program name.
48 With methods 2 and 3, Perl starts parsing the input file from the
49 beginning, unless you've specified a B<-x> switch, in which case it
50 scans for the first line starting with #! and containing the word
51 "perl", and starts there instead. This is useful for running a program
52 embedded in a larger message. (In this case you would indicate the end
53 of the program using the C<__END__> token.)
55 The #! line is always examined for switches as the line is being
56 parsed. Thus, if you're on a machine that allows only one argument
57 with the #! line, or worse, doesn't even recognize the #! line, you
58 still can get consistent switch behavior regardless of how Perl was
59 invoked, even if B<-x> was used to find the beginning of the program.
61 Because historically some operating systems silently chopped off
62 kernel interpretation of the #! line after 32 characters, some
63 switches may be passed in on the command line, and some may not;
64 you could even get a "-" without its letter, if you're not careful.
65 You probably want to make sure that all your switches fall either
66 before or after that 32-character boundary. Most switches don't
67 actually care if they're processed redundantly, but getting a "-"
68 instead of a complete switch could cause Perl to try to execute
69 standard input instead of your program. And a partial B<-I> switch
70 could also cause odd results.
72 Some switches do care if they are processed twice, for instance
73 combinations of B<-l> and B<-0>. Either put all the switches after
74 the 32-character boundary (if applicable), or replace the use of
75 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
77 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
78 The sequences "-*" and "- " are specifically ignored so that you could,
79 if you were so inclined, say
81 #!/bin/sh -- # -*- perl -*- -p
82 eval 'exec perl -wS $0 ${1+"$@"}'
83 if $running_under_some_shell;
85 to let Perl see the B<-p> switch.
87 A similar trick involves the B<env> program, if you have it.
91 The examples above use a relative path to the perl interpreter,
92 getting whatever version is first in the user's path. If you want
93 a specific version of Perl, say, perl5.005_57, you should place
94 that directly in the #! line's path.
96 If the #! line does not contain the word "perl", the program named after
97 the #! is executed instead of the Perl interpreter. This is slightly
98 bizarre, but it helps people on machines that don't do #!, because they
99 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
100 dispatch the program to the correct interpreter for them.
102 After locating your program, Perl compiles the entire program to an
103 internal form. If there are any compilation errors, execution of the
104 program is not attempted. (This is unlike the typical shell script,
105 which might run part-way through before finding a syntax error.)
107 If the program is syntactically correct, it is executed. If the program
108 runs off the end without hitting an exit() or die() operator, an implicit
109 C<exit(0)> is provided to indicate successful completion.
111 =head2 #! and quoting on non-Unix systems
113 Unix's #! technique can be simulated on other systems:
121 extproc perl -S -your_switches
123 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
128 Create a batch file to run your program, and codify it in
129 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
130 distribution for more information).
134 The Win95/NT installation, when using the ActiveState installer for Perl,
135 will modify the Registry to associate the F<.pl> extension with the perl
136 interpreter. If you install Perl by other means (including building from
137 the sources), you may have to modify the Registry yourself. Note that
138 this means you can no longer tell the difference between an executable
139 Perl program and a Perl library file.
143 A Macintosh perl program will have the appropriate Creator and
144 Type, so that double-clicking them will invoke the perl application.
150 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
151 $ exit++ + ++$status != 0 and $exit = $status = undef;
153 at the top of your program, where B<-mysw> are any command line switches you
154 want to pass to Perl. You can now invoke the program directly, by saying
155 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
156 via F<DCL$PATH> by just using the name of the program).
158 This incantation is a bit much to remember, but Perl will display it for
159 you if you say C<perl "-V:startperl">.
163 Command-interpreters on non-Unix systems have rather different ideas
164 on quoting than Unix shells. You'll need to learn the special
165 characters in your command-interpreter (C<*>, C<\> and C<"> are
166 common) and how to protect whitespace and these characters to run
167 one-liners (see B<-e> below).
169 On some systems, you may have to change single-quotes to double ones,
170 which you must I<not> do on Unix or Plan 9 systems. You might also
171 have to change a single % to a %%.
176 perl -e 'print "Hello world\n"'
179 perl -e "print \"Hello world\n\""
182 print "Hello world\n"
183 (then Run "Myscript" or Shift-Command-R)
186 perl -e "print ""Hello world\n"""
188 The problem is that none of this is reliable: it depends on the
189 command and it is entirely possible neither works. If B<4DOS> were
190 the command shell, this would probably work better:
192 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
194 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
195 when nobody was looking, but just try to find documentation for its
198 Under the Macintosh, it depends which environment you are using. The MacPerl
199 shell, or MPW, is much like Unix shells in its support for several
200 quoting variants, except that it makes free use of the Macintosh's non-ASCII
201 characters as control characters.
203 There is no general solution to all of this. It's just a mess.
205 =head2 Location of Perl
207 It may seem obvious to say, but Perl is useful only when users can
208 easily find it. When possible, it's good for both F</usr/bin/perl>
209 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
210 that can't be done, system administrators are strongly encouraged
211 to put (symlinks to) perl and its accompanying utilities into a
212 directory typically found along a user's PATH, or in some other
213 obvious and convenient place.
215 In this documentation, C<#!/usr/bin/perl> on the first line of the program
216 will stand in for whatever method works on your system. You are
217 advised to use a specific path if you care about a specific version.
219 #!/usr/local/bin/perl5.00554
221 or if you just want to be running at least version, place a statement
222 like this at the top of your program:
226 =head2 Command Switches
228 As with all standard commands, a single-character switch may be
229 clustered with the following switch, if any.
231 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
237 =item B<-0>[I<digits>]
239 specifies the input record separator (C<$/>) as an octal number. If there are
240 no digits, the null character is the separator. Other switches may
241 precede or follow the digits. For example, if you have a version of
242 B<find> which can print filenames terminated by the null character, you
245 find . -name '*.orig' -print0 | perl -n0e unlink
247 The special value 00 will cause Perl to slurp files in paragraph mode.
248 The value 0777 will cause Perl to slurp files whole because there is no
249 legal character with that value.
253 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
254 split command to the @F array is done as the first thing inside the
255 implicit while loop produced by the B<-n> or B<-p>.
257 perl -ane 'print pop(@F), "\n";'
266 An alternate delimiter may be specified using B<-F>.
268 =item B<-C[:boolean]>
270 enables Perl to use the Unicode APIs on the target system. A bare C<-C>
271 enables, C<-C:1> also enables, and C<-C:0> disables.
273 As of Perl 5.8.1, if C<-C> is used and the locale settings (the LC_ALL,
274 LC_CTYPE, and LANG environment variables) indicate a UTF-8 locale,
275 the STDIN is expected to be in UTF-8, the STDOUT and STDERR are
276 expected to be in UTF-8, and C<:utf8> is the default file open layer.
277 See L<perluniintro>, L<perlfunc/open>, and L<open> for more information.
278 The magic variable C<${^UTF8_LOCALE}> reflects this state,
279 see L<perlvar/"${^UTF8_LOCALE}">. (Another way of setting this
280 variable is to set the environment variable PERL_UTF8_LOCALE.)
282 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
283 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
284 This feature was practically unused, however, and the command line
285 switch was therefore "recycled".)
289 causes Perl to check the syntax of the program and then exit without
290 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
291 C<use> blocks, because these are considered as occurring outside the
292 execution of your program. C<INIT> and C<END> blocks, however, will
297 runs the program under the Perl debugger. See L<perldebug>.
299 =item B<-d:>I<foo[=bar,baz]>
301 runs the program under the control of a debugging, profiling, or
302 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
303 the program using the Devel::DProf profiler. As with the B<-M>
304 flag, options may be passed to the Devel::foo package where they
305 will be received and interpreted by the Devel::foo::import routine.
306 The comma-separated list of options must follow a C<=> character.
309 =item B<-D>I<letters>
313 sets debugging flags. To watch how it executes your program, use
314 B<-Dtls>. (This works only if debugging is compiled into your
315 Perl.) Another nice value is B<-Dx>, which lists your compiled
316 syntax tree. And B<-Dr> displays compiled regular expressions;
317 the format of the output is explained in L<perldebguts>.
319 As an alternative, specify a number instead of list of letters (e.g.,
320 B<-D14> is equivalent to B<-Dtls>):
322 1 p Tokenizing and parsing
324 with v, displays all stacks
325 4 l Context (loop) stack processing
327 16 o Method and overloading resolution
328 32 c String/numeric conversions
329 64 P Print profiling info, preprocessor command for -P, source file input state
330 128 m Memory allocation
331 256 f Format processing
332 512 r Regular expression parsing and execution
333 1024 x Syntax tree dump
334 2048 u Tainting checks
335 4096 (Obsolete, previously used for LEAKTEST)
336 8192 H Hash dump -- usurps values()
337 16384 X Scratchpad allocation
339 65536 S Thread synchronization
341 262144 R Include reference counts of dumped variables (eg when using -Ds)
342 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
343 1048576 v Verbose: use in conjunction with other flags
344 2097152 C Copy On Write
346 All these flags require B<-DDEBUGGING> when you compile the Perl
347 executable (but see L<Devel::Peek>, L<re> which may change this).
348 See the F<INSTALL> file in the Perl source distribution
349 for how to do this. This flag is automatically set if you include B<-g>
350 option when C<Configure> asks you about optimizer/debugger flags.
352 If you're just trying to get a print out of each line of Perl code
353 as it executes, the way that C<sh -x> provides for shell scripts,
354 you can't use Perl's B<-D> switch. Instead do this
356 # If you have "env" utility
357 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
359 # Bourne shell syntax
360 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
363 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
365 See L<perldebug> for details and variations.
367 =item B<-e> I<commandline>
369 may be used to enter one line of program. If B<-e> is given, Perl
370 will not look for a filename in the argument list. Multiple B<-e>
371 commands may be given to build up a multi-line script. Make sure
372 to use semicolons where you would in a normal program.
374 =item B<-F>I<pattern>
376 specifies the pattern to split on if B<-a> is also in effect. The
377 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
378 put in single quotes.
382 prints a summary of the options.
384 =item B<-i>[I<extension>]
386 specifies that files processed by the C<E<lt>E<gt>> construct are to be
387 edited in-place. It does this by renaming the input file, opening the
388 output file by the original name, and selecting that output file as the
389 default for print() statements. The extension, if supplied, is used to
390 modify the name of the old file to make a backup copy, following these
393 If no extension is supplied, no backup is made and the current file is
396 If the extension doesn't contain a C<*>, then it is appended to the
397 end of the current filename as a suffix. If the extension does
398 contain one or more C<*> characters, then each C<*> is replaced
399 with the current filename. In Perl terms, you could think of this
402 ($backup = $extension) =~ s/\*/$file_name/g;
404 This allows you to add a prefix to the backup file, instead of (or in
405 addition to) a suffix:
407 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
409 Or even to place backup copies of the original files into another
410 directory (provided the directory already exists):
412 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
414 These sets of one-liners are equivalent:
416 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
417 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
419 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
420 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
422 From the shell, saying
424 $ perl -p -i.orig -e "s/foo/bar/; ... "
426 is the same as using the program:
428 #!/usr/bin/perl -pi.orig
431 which is equivalent to
434 $extension = '.orig';
436 if ($ARGV ne $oldargv) {
437 if ($extension !~ /\*/) {
438 $backup = $ARGV . $extension;
441 ($backup = $extension) =~ s/\*/$ARGV/g;
443 rename($ARGV, $backup);
444 open(ARGVOUT, ">$ARGV");
451 print; # this prints to original filename
455 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
456 know when the filename has changed. It does, however, use ARGVOUT for
457 the selected filehandle. Note that STDOUT is restored as the default
458 output filehandle after the loop.
460 As shown above, Perl creates the backup file whether or not any output
461 is actually changed. So this is just a fancy way to copy files:
463 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
465 $ perl -p -i'.orig' -e 1 file1 file2 file3...
467 You can use C<eof> without parentheses to locate the end of each input
468 file, in case you want to append to each file, or reset line numbering
469 (see example in L<perlfunc/eof>).
471 If, for a given file, Perl is unable to create the backup file as
472 specified in the extension then it will skip that file and continue on
473 with the next one (if it exists).
475 For a discussion of issues surrounding file permissions and B<-i>,
476 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?>.
478 You cannot use B<-i> to create directories or to strip extensions from
481 Perl does not expand C<~> in filenames, which is good, since some
482 folks use it for their backup files:
484 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
486 Finally, the B<-i> switch does not impede execution when no
487 files are given on the command line. In this case, no backup is made
488 (the original file cannot, of course, be determined) and processing
489 proceeds from STDIN to STDOUT as might be expected.
491 =item B<-I>I<directory>
493 Directories specified by B<-I> are prepended to the search path for
494 modules (C<@INC>), and also tells the C preprocessor where to search for
495 include files. The C preprocessor is invoked with B<-P>; by default it
496 searches /usr/include and /usr/lib/perl.
498 =item B<-l>[I<octnum>]
500 enables automatic line-ending processing. It has two separate
501 effects. First, it automatically chomps C<$/> (the input record
502 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
503 (the output record separator) to have the value of I<octnum> so
504 that any print statements will have that separator added back on.
505 If I<octnum> is omitted, sets C<$\> to the current value of
506 C<$/>. For instance, to trim lines to 80 columns:
508 perl -lpe 'substr($_, 80) = ""'
510 Note that the assignment C<$\ = $/> is done when the switch is processed,
511 so the input record separator can be different than the output record
512 separator if the B<-l> switch is followed by a B<-0> switch:
514 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
516 This sets C<$\> to newline and then sets C<$/> to the null character.
518 =item B<-m>[B<->]I<module>
520 =item B<-M>[B<->]I<module>
522 =item B<-M>[B<->]I<'module ...'>
524 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
526 B<-m>I<module> executes C<use> I<module> C<();> before executing your
529 B<-M>I<module> executes C<use> I<module> C<;> before executing your
530 program. You can use quotes to add extra code after the module name,
531 e.g., C<'-Mmodule qw(foo bar)'>.
533 If the first character after the B<-M> or B<-m> is a dash (C<->)
534 then the 'use' is replaced with 'no'.
536 A little builtin syntactic sugar means you can also say
537 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
538 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
539 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
540 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
541 removes the distinction between B<-m> and B<-M>.
545 causes Perl to assume the following loop around your program, which
546 makes it iterate over filename arguments somewhat like B<sed -n> or
551 ... # your program goes here
554 Note that the lines are not printed by default. See B<-p> to have
555 lines printed. If a file named by an argument cannot be opened for
556 some reason, Perl warns you about it and moves on to the next file.
558 Here is an efficient way to delete all files older than a week:
560 find . -mtime +7 -print | perl -nle unlink
562 This is faster than using the B<-exec> switch of B<find> because you don't
563 have to start a process on every filename found. It does suffer from
564 the bug of mishandling newlines in pathnames, which you can fix if
565 you follow the example under B<-0>.
567 C<BEGIN> and C<END> blocks may be used to capture control before or after
568 the implicit program loop, just as in B<awk>.
572 causes Perl to assume the following loop around your program, which
573 makes it iterate over filename arguments somewhat like B<sed>:
578 ... # your program goes here
580 print or die "-p destination: $!\n";
583 If a file named by an argument cannot be opened for some reason, Perl
584 warns you about it, and moves on to the next file. Note that the
585 lines are printed automatically. An error occurring during printing is
586 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
587 overrides a B<-n> switch.
589 C<BEGIN> and C<END> blocks may be used to capture control before or after
590 the implicit loop, just as in B<awk>.
594 B<NOTE: Use of -P is strongly discouraged because of its inherent
595 problems, including poor portability.>
597 This option causes your program to be run through the C preprocessor before
598 compilation by Perl. Because both comments and B<cpp> directives begin
599 with the # character, you should avoid starting comments with any words
600 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
602 If you're considering using C<-P>, you might also want to look at the
603 Filter::cpp module from CPAN.
605 The problems of -P include, but are not limited to:
611 The C<#!> line is stripped, so any switches there don't apply.
615 A C<-P> on a C<#!> line doesn't work.
619 B<All> lines that begin with (whitespace and) a C<#> but
620 do not look like cpp commands, are stripped, including anything
621 inside Perl strings, regular expressions, and here-docs .
625 In some platforms the C preprocessor knows too much: it knows about
626 the C++ -style until-end-of-line comments starting with C<"//">.
627 This will cause problems with common Perl constructs like
631 because after -P this will became illegal code
635 The workaround is to use some other quoting separator than C<"/">,
636 like for example C<"!">:
644 It requires not only a working C preprocessor but also a working
645 F<sed>. If not on UNIX, you are probably out of luck on this.
649 Script line numbers are not preserved.
653 The C<-x> does not work with C<-P>.
659 enables rudimentary switch parsing for switches on the command
660 line after the program name but before any filename arguments (or before
661 an argument of B<-->). This means you can have switches with two leading
662 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
663 corresponding variable in the Perl program. The following program
664 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
665 if it is invoked with B<-xyz=abc>.
668 if ($xyz) { print "$xyz\n" }
670 Do note that B<--help> creates the variable ${-help}, which is not compliant
675 makes Perl use the PATH environment variable to search for the
676 program (unless the name of the program contains directory separators).
678 On some platforms, this also makes Perl append suffixes to the
679 filename while searching for it. For example, on Win32 platforms,
680 the ".bat" and ".cmd" suffixes are appended if a lookup for the
681 original name fails, and if the name does not already end in one
682 of those suffixes. If your Perl was compiled with DEBUGGING turned
683 on, using the -Dp switch to Perl shows how the search progresses.
685 Typically this is used to emulate #! startup on platforms that
686 don't support #!. This example works on many platforms that
687 have a shell compatible with Bourne shell:
690 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
691 if $running_under_some_shell;
693 The system ignores the first line and feeds the program to F</bin/sh>,
694 which proceeds to try to execute the Perl program as a shell script.
695 The shell executes the second line as a normal shell command, and thus
696 starts up the Perl interpreter. On some systems $0 doesn't always
697 contain the full pathname, so the B<-S> tells Perl to search for the
698 program if necessary. After Perl locates the program, it parses the
699 lines and ignores them because the variable $running_under_some_shell
700 is never true. If the program will be interpreted by csh, you will need
701 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
702 embedded spaces (and such) in the argument list. To start up sh rather
703 than csh, some systems may have to replace the #! line with a line
704 containing just a colon, which will be politely ignored by Perl. Other
705 systems can't control that, and need a totally devious construct that
706 will work under any of B<csh>, B<sh>, or Perl, such as the following:
708 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
709 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
710 if $running_under_some_shell;
712 If the filename supplied contains directory separators (i.e., is an
713 absolute or relative pathname), and if that file is not found,
714 platforms that append file extensions will do so and try to look
715 for the file with those extensions added, one by one.
717 On DOS-like platforms, if the program does not contain directory
718 separators, it will first be searched for in the current directory
719 before being searched for on the PATH. On Unix platforms, the
720 program will be searched for strictly on the PATH.
724 Like B<-T>, but taint checks will issue warnings rather than fatal
725 errors. These warnings can be controlled normally with C<no warnings
728 B<NOTE: this is not a substitute for -T.> This is meant only to be
729 used as a temporary development aid while securing legacy code:
730 for real production code and for new secure code written from scratch
731 always use the real B<-T>.
735 forces "taint" checks to be turned on so you can test them. Ordinarily
736 these checks are done only when running setuid or setgid. It's a
737 good idea to turn them on explicitly for programs that run on behalf
738 of someone else whom you might not necessarily trust, such as CGI
739 programs or any internet servers you might write in Perl. See
740 L<perlsec> for details. For security reasons, this option must be
741 seen by Perl quite early; usually this means it must appear early
742 on the command line or in the #! line for systems which support
747 This obsolete switch causes Perl to dump core after compiling your
748 program. You can then in theory take this core dump and turn it
749 into an executable file by using the B<undump> program (not supplied).
750 This speeds startup at the expense of some disk space (which you
751 can minimize by stripping the executable). (Still, a "hello world"
752 executable comes out to about 200K on my machine.) If you want to
753 execute a portion of your program before dumping, use the dump()
754 operator instead. Note: availability of B<undump> is platform
755 specific and may not be available for a specific port of Perl.
757 This switch has been superseded in favor of the new Perl code
758 generator backends to the compiler. See L<B> and L<B::Bytecode>
763 allows Perl to do unsafe operations. Currently the only "unsafe"
764 operations are the unlinking of directories while running as superuser,
765 and running setuid programs with fatal taint checks turned into
766 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
767 be used along with this option to actually I<generate> the
768 taint-check warnings.
772 prints the version and patchlevel of your perl executable.
776 prints summary of the major perl configuration values and the current
781 Prints to STDOUT the value of the named configuration variable.
786 will provide strong clues about what your MANPATH variable should
787 be set to in order to access the Perl documentation.
791 prints warnings about dubious constructs, such as variable names
792 that are mentioned only once and scalar variables that are used
793 before being set, redefined subroutines, references to undefined
794 filehandles or filehandles opened read-only that you are attempting
795 to write on, values used as a number that doesn't look like numbers,
796 using an array as though it were a scalar, if your subroutines
797 recurse more than 100 deep, and innumerable other things.
799 This switch really just enables the internal C<$^W> variable. You
800 can disable or promote into fatal errors specific warnings using
801 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
802 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
803 facility is also available if you want to manipulate entire classes
804 of warnings; see L<warnings> or L<perllexwarn>.
808 Enables all warnings regardless of C<no warnings> or C<$^W>.
813 Disables all warnings regardless of C<use warnings> or C<$^W>.
816 =item B<-x> I<directory>
818 tells Perl that the program is embedded in a larger chunk of unrelated
819 ASCII text, such as in a mail message. Leading garbage will be
820 discarded until the first line that starts with #! and contains the
821 string "perl". Any meaningful switches on that line will be applied.
822 If a directory name is specified, Perl will switch to that directory
823 before running the program. The B<-x> switch controls only the
824 disposal of leading garbage. The program must be terminated with
825 C<__END__> if there is trailing garbage to be ignored (the program
826 can process any or all of the trailing garbage via the DATA filehandle
837 Used if chdir has no argument.
841 Used if chdir has no argument and HOME is not set.
845 Used in executing subprocesses, and in finding the program if B<-S> is
850 A colon-separated list of directories in which to look for Perl library
851 files before looking in the standard library and the current
852 directory. Any architecture-specific directories under the specified
853 locations are automatically included if they exist. If PERL5LIB is not
854 defined, PERLLIB is used.
856 When running taint checks (either because the program was running setuid
857 or setgid, or the B<-T> switch was used), neither variable is used.
858 The program should instead say:
860 use lib "/my/directory";
864 Command-line options (switches). Switches in this variable are taken
865 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
866 switches are allowed. When running taint checks (because the program
867 was running setuid or setgid, or the B<-T> switch was used), this
868 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
869 enabled, and any subsequent options ignored.
873 A space (or colon) separated list of PerlIO layers. If perl is built
874 to use PerlIO system for IO (the default) these layers effect perl's IO.
876 It is conventional to start layer names with a colon e.g. C<:perlio> to
877 emphasise their similarity to variable "attributes". But the code that parses
878 layer specification strings (which is also used to decode the PERLIO
879 environment variable) treats the colon as a separator.
881 The list becomes the default for I<all> perl's IO. Consequently only built-in
882 layers can appear in this list, as external layers (such as :encoding()) need
883 IO in order to load them!. See L<"open pragma"|open> for how to add external
884 encodings as defaults.
886 The layers that it makes sense to include in the PERLIO environment
887 variable are summarised below. For more details see L<PerlIO>.
893 Turns I<off> the C<:utf8> flag for the layer below.
894 Unlikely to be useful in global PERLIO environment variable.
898 A layer that implements DOS/Windows like CRLF line endings.
899 On read converts pairs of CR,LF to a single "\n" newline character.
900 On write converts each "\n" to a CR,LF pair.
901 Based on the C<:perlio> layer.
905 A layer which implements "reading" of files by using C<mmap()> to
906 make (whole) file appear in the process's address space, and then
907 using that as PerlIO's "buffer". This I<may> be faster in certain
908 circumstances for large files, and may result in less physical memory
909 use when multiple processes are reading the same file.
911 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
912 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
913 needs extra house-keeping (to extend the file) which negates any advantage.
915 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
919 A from scratch implementation of buffering for PerlIO. Provides fast
920 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
921 and in general attempts to minimize data copying.
923 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
927 Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
928 It makes the stream pass each byte as-is without any translation.
929 In particular CRLF translation, and/or :utf8 inuited from locale
932 Arranges for all accesses go straight to the lowest buffered layer provided
933 by the configration. That is it strips off any layers above that layer.
935 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
936 referred to as a "discipline") is documented as the inverse of the
937 C<:crlf> layer. That is no longer the case - other layers which would
938 alter binary nature of the stream are also disabled. If you want UNIX
939 line endings on a platform that normally does CRLF translation, but still
940 want UTF-8 or encoding defaults the appropriate thing to do is to add
941 C<:perlio> to PERLIO environment variable.
945 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
946 library calls. The layer provides both buffering and IO.
947 Note that C<:stdio> layer does I<not> do CRLF translation even if that
948 is platforms normal behaviour. You will need a C<:crlf> layer above it
953 Lowest level layer which provides basic PerlIO operations in terms of
954 UNIX/POSIX numeric file descriptor calls
955 C<open(), read(), write(), lseek(), close()>
959 Turns on a flag on the layer below to tell perl that data sent to the
960 stream should be converted to perl internal "utf8" form and that data from the
961 stream should be considered as so encoded. On ASCII based platforms the
962 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
963 May be useful in PERLIO environment variable to make UTF-8 the
964 default. (To turn off that behaviour use C<:bytes> layer.)
968 On Win32 platforms this I<experimental> layer uses native "handle" IO
969 rather than unix-like numeric file descriptor layer. Known to be
970 buggy in this release.
974 On all platforms the default set of layers should give acceptable results.
976 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
977 Configure is setup to prefer "stdio" implementation if system's library
978 provides for fast access to the buffer, otherwise it uses the "unix perlio"
981 On Win32 the default in this release is "unix crlf". Win32's "stdio"
982 has a number of bugs/mis-features for perl IO which are somewhat
983 C compiler vendor/version dependent. Using our own C<crlf> layer as
984 the buffer avoids those issues and makes things more uniform.
985 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
988 This release uses C<unix> as the bottom layer on Win32 and so still uses C
989 compiler's numeric file descriptor routines. There is an experimental native
990 C<win32> layer which is expected to be enhanced and should eventually replace
995 If set to the name of a file or device then certain operations of PerlIO
996 sub-system will be logged to that file (opened as append). Typical uses
999 PERLIO_DEBUG=/dev/tty perl script ...
1001 and Win32 approximate equivalent:
1003 set PERLIO_DEBUG=CON
1009 A colon-separated list of directories in which to look for Perl library
1010 files before looking in the standard library and the current directory.
1011 If PERL5LIB is defined, PERLLIB is not used.
1015 The command used to load the debugger code. The default is:
1017 BEGIN { require 'perl5db.pl' }
1019 =item PERL5SHELL (specific to the Win32 port)
1021 May be set to an alternative shell that perl must use internally for
1022 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1023 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1024 to be space-separated. Precede any character that needs to be protected
1025 (like a space or backslash) with a backslash.
1027 Note that Perl doesn't use COMSPEC for this purpose because
1028 COMSPEC has a high degree of variability among users, leading to
1029 portability concerns. Besides, perl can use a shell that may not be
1030 fit for interactive use, and setting COMSPEC to such a shell may
1031 interfere with the proper functioning of other programs (which usually
1032 look in COMSPEC to find a shell fit for interactive use).
1034 =item PERL_DEBUG_MSTATS
1036 Relevant only if perl is compiled with the malloc included with the perl
1037 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1038 If set, this causes memory statistics to be dumped after execution. If set
1039 to an integer greater than one, also causes memory statistics to be dumped
1042 =item PERL_DESTRUCT_LEVEL
1044 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1045 this controls the behavior of global destruction of objects and other
1046 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1050 If using the C<encoding> pragma without an explicit encoding name, the
1051 PERL_ENCODING environment variable is consulted for an encoding name.
1053 =item PERL_ROOT (specific to the VMS port)
1055 A translation concealed rooted logical name that contains perl and the
1056 logical device for the @INC path on VMS only. Other logical names that
1057 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1058 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1059 L<perlvms> and in F<README.vms> in the Perl source distribution.
1061 =item PERL_UTF8_LOCALE
1063 Equivalent to the B<-C> command-line switch.
1065 =item SYS$LOGIN (specific to the VMS port)
1067 Used if chdir has no argument and HOME and LOGDIR are not set.
1071 Perl also has environment variables that control how Perl handles data
1072 specific to particular natural languages. See L<perllocale>.
1074 Apart from these, Perl uses no other environment variables, except
1075 to make them available to the program being executed, and to child
1076 processes. However, programs running setuid would do well to execute
1077 the following lines before doing anything else, just to keep people
1080 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1081 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1082 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};