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/hexadecimal>] ]>
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<number/list>] >]> ]>
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<octal/hexadecimal>]
239 specifies the input record separator (C<$/>) as an octal or
240 hexadecimal number. If there are no digits, the null character is the
241 separator. Other switches may precede or follow the digits. For
242 example, if you have a version of B<find> which can print filenames
243 terminated by the null character, you can say this:
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 byte with that value.
251 If you want to specify any Unicode character, use the hexadecimal
252 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
253 (This means that you cannot use the C<-x> with a directory name that
254 consists of hexadecimal digits.)
258 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
259 split command to the @F array is done as the first thing inside the
260 implicit while loop produced by the B<-n> or B<-p>.
262 perl -ane 'print pop(@F), "\n";'
271 An alternate delimiter may be specified using B<-F>.
273 =item B<-C [I<number/list>]>
275 The C<-C> flag controls some Unicode of the Perl Unicode features.
277 As of 5.8.1, the C<-C> can be followed either by a number or a list
278 of option letters. The letters, their numeric values, and effects
279 are as follows; listing the letters is equal to summing the numbers.
281 I 1 STDIN is assumed to be in UTF-8
282 O 2 STDOUT will be in UTF-8
283 E 4 STDERR will be in UTF-8
285 i 8 UTF-8 is the default PerlIO layer for input streams
286 o 16 UTF-8 is the default PerlIO layer for output streams
288 A 32 the @ARGV elements are expected to be strings encoded in UTF-8
289 L 64 normally the "IOEioA" are unconditional,
290 the L makes them conditional on the locale environment
291 variables (the LC_ALL, LC_TYPE, and LANG, in the order
292 of decreasing precedence) -- if the variables indicate
293 UTF-8, then the selected "IOEioA" are in effect
295 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
296 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
299 The C<io> options mean that any subsequent open() (or similar I/O
300 operations) will have the C<:utf8> PerlIO layer implicitly applied
301 to them, in other words, UTF-8 is expected from any input stream,
302 and UTF-8 is produced to any output stream. This is just the default,
303 with explicit layers in open() and with binmode() one can manipulate
306 C<-C> on its own (not followed by any number or option list), or the
307 empty string C<""> for the C<$ENV{PERL_UNICODE}, has the same effect
308 as <-CSDL>. In other words, the standard I/O handles and the default
309 C<open()> layer are UTF-8-fied B<but> only if the locale environment
310 variables indicate a UTF-8 locale. This behaviour follows the
311 I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
313 You can use C<-C0> (or C<"0"> for $ENV{PERL_UNICODE}) to explicitly
314 disable all the above Unicode features.
316 The read-only magic variable C<${^UNICODE}> reflects the numeric value
317 of this setting. This is variable is set during Perl startup and is
318 thereafter read-only. If you want runtime effects, use the three-arg
319 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
320 and the C<open> pragma (see L<open>).
322 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
323 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
324 This feature was practically unused, however, and the command line
325 switch was therefore "recycled".)
329 causes Perl to check the syntax of the program and then exit without
330 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
331 C<use> blocks, because these are considered as occurring outside the
332 execution of your program. C<INIT> and C<END> blocks, however, will
337 runs the program under the Perl debugger. See L<perldebug>.
339 =item B<-d:>I<foo[=bar,baz]>
341 runs the program under the control of a debugging, profiling, or
342 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
343 the program using the Devel::DProf profiler. As with the B<-M>
344 flag, options may be passed to the Devel::foo package where they
345 will be received and interpreted by the Devel::foo::import routine.
346 The comma-separated list of options must follow a C<=> character.
349 =item B<-D>I<letters>
353 sets debugging flags. To watch how it executes your program, use
354 B<-Dtls>. (This works only if debugging is compiled into your
355 Perl.) Another nice value is B<-Dx>, which lists your compiled
356 syntax tree. And B<-Dr> displays compiled regular expressions;
357 the format of the output is explained in L<perldebguts>.
359 As an alternative, specify a number instead of list of letters (e.g.,
360 B<-D14> is equivalent to B<-Dtls>):
362 1 p Tokenizing and parsing
364 with v, displays all stacks
365 4 l Context (loop) stack processing
367 16 o Method and overloading resolution
368 32 c String/numeric conversions
369 64 P Print profiling info, preprocessor command for -P, source file input state
370 128 m Memory allocation
371 256 f Format processing
372 512 r Regular expression parsing and execution
373 1024 x Syntax tree dump
374 2048 u Tainting checks
375 4096 (Obsolete, previously used for LEAKTEST)
376 8192 H Hash dump -- usurps values()
377 16384 X Scratchpad allocation
379 65536 S Thread synchronization
381 262144 R Include reference counts of dumped variables (eg when using -Ds)
382 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
383 1048576 v Verbose: use in conjunction with other flags
384 2097152 C Copy On Write
386 All these flags require B<-DDEBUGGING> when you compile the Perl
387 executable (but see L<Devel::Peek>, L<re> which may change this).
388 See the F<INSTALL> file in the Perl source distribution
389 for how to do this. This flag is automatically set if you include B<-g>
390 option when C<Configure> asks you about optimizer/debugger flags.
392 If you're just trying to get a print out of each line of Perl code
393 as it executes, the way that C<sh -x> provides for shell scripts,
394 you can't use Perl's B<-D> switch. Instead do this
396 # If you have "env" utility
397 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
399 # Bourne shell syntax
400 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
403 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
405 See L<perldebug> for details and variations.
407 =item B<-e> I<commandline>
409 may be used to enter one line of program. If B<-e> is given, Perl
410 will not look for a filename in the argument list. Multiple B<-e>
411 commands may be given to build up a multi-line script. Make sure
412 to use semicolons where you would in a normal program.
414 =item B<-F>I<pattern>
416 specifies the pattern to split on if B<-a> is also in effect. The
417 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
418 put in single quotes.
422 prints a summary of the options.
424 =item B<-i>[I<extension>]
426 specifies that files processed by the C<E<lt>E<gt>> construct are to be
427 edited in-place. It does this by renaming the input file, opening the
428 output file by the original name, and selecting that output file as the
429 default for print() statements. The extension, if supplied, is used to
430 modify the name of the old file to make a backup copy, following these
433 If no extension is supplied, no backup is made and the current file is
436 If the extension doesn't contain a C<*>, then it is appended to the
437 end of the current filename as a suffix. If the extension does
438 contain one or more C<*> characters, then each C<*> is replaced
439 with the current filename. In Perl terms, you could think of this
442 ($backup = $extension) =~ s/\*/$file_name/g;
444 This allows you to add a prefix to the backup file, instead of (or in
445 addition to) a suffix:
447 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
449 Or even to place backup copies of the original files into another
450 directory (provided the directory already exists):
452 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
454 These sets of one-liners are equivalent:
456 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
457 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
459 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
460 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
462 From the shell, saying
464 $ perl -p -i.orig -e "s/foo/bar/; ... "
466 is the same as using the program:
468 #!/usr/bin/perl -pi.orig
471 which is equivalent to
474 $extension = '.orig';
476 if ($ARGV ne $oldargv) {
477 if ($extension !~ /\*/) {
478 $backup = $ARGV . $extension;
481 ($backup = $extension) =~ s/\*/$ARGV/g;
483 rename($ARGV, $backup);
484 open(ARGVOUT, ">$ARGV");
491 print; # this prints to original filename
495 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
496 know when the filename has changed. It does, however, use ARGVOUT for
497 the selected filehandle. Note that STDOUT is restored as the default
498 output filehandle after the loop.
500 As shown above, Perl creates the backup file whether or not any output
501 is actually changed. So this is just a fancy way to copy files:
503 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
505 $ perl -p -i'.orig' -e 1 file1 file2 file3...
507 You can use C<eof> without parentheses to locate the end of each input
508 file, in case you want to append to each file, or reset line numbering
509 (see example in L<perlfunc/eof>).
511 If, for a given file, Perl is unable to create the backup file as
512 specified in the extension then it will skip that file and continue on
513 with the next one (if it exists).
515 For a discussion of issues surrounding file permissions and B<-i>,
516 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?>.
518 You cannot use B<-i> to create directories or to strip extensions from
521 Perl does not expand C<~> in filenames, which is good, since some
522 folks use it for their backup files:
524 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
526 Finally, the B<-i> switch does not impede execution when no
527 files are given on the command line. In this case, no backup is made
528 (the original file cannot, of course, be determined) and processing
529 proceeds from STDIN to STDOUT as might be expected.
531 =item B<-I>I<directory>
533 Directories specified by B<-I> are prepended to the search path for
534 modules (C<@INC>), and also tells the C preprocessor where to search for
535 include files. The C preprocessor is invoked with B<-P>; by default it
536 searches /usr/include and /usr/lib/perl.
538 =item B<-l>[I<octnum>]
540 enables automatic line-ending processing. It has two separate
541 effects. First, it automatically chomps C<$/> (the input record
542 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
543 (the output record separator) to have the value of I<octnum> so
544 that any print statements will have that separator added back on.
545 If I<octnum> is omitted, sets C<$\> to the current value of
546 C<$/>. For instance, to trim lines to 80 columns:
548 perl -lpe 'substr($_, 80) = ""'
550 Note that the assignment C<$\ = $/> is done when the switch is processed,
551 so the input record separator can be different than the output record
552 separator if the B<-l> switch is followed by a B<-0> switch:
554 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
556 This sets C<$\> to newline and then sets C<$/> to the null character.
558 =item B<-m>[B<->]I<module>
560 =item B<-M>[B<->]I<module>
562 =item B<-M>[B<->]I<'module ...'>
564 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
566 B<-m>I<module> executes C<use> I<module> C<();> before executing your
569 B<-M>I<module> executes C<use> I<module> C<;> before executing your
570 program. You can use quotes to add extra code after the module name,
571 e.g., C<'-Mmodule qw(foo bar)'>.
573 If the first character after the B<-M> or B<-m> is a dash (C<->)
574 then the 'use' is replaced with 'no'.
576 A little builtin syntactic sugar means you can also say
577 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
578 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
579 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
580 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
581 removes the distinction between B<-m> and B<-M>.
585 causes Perl to assume the following loop around your program, which
586 makes it iterate over filename arguments somewhat like B<sed -n> or
591 ... # your program goes here
594 Note that the lines are not printed by default. See B<-p> to have
595 lines printed. If a file named by an argument cannot be opened for
596 some reason, Perl warns you about it and moves on to the next file.
598 Here is an efficient way to delete all files older than a week:
600 find . -mtime +7 -print | perl -nle unlink
602 This is faster than using the B<-exec> switch of B<find> because you don't
603 have to start a process on every filename found. It does suffer from
604 the bug of mishandling newlines in pathnames, which you can fix if
605 you follow the example under B<-0>.
607 C<BEGIN> and C<END> blocks may be used to capture control before or after
608 the implicit program loop, just as in B<awk>.
612 causes Perl to assume the following loop around your program, which
613 makes it iterate over filename arguments somewhat like B<sed>:
618 ... # your program goes here
620 print or die "-p destination: $!\n";
623 If a file named by an argument cannot be opened for some reason, Perl
624 warns you about it, and moves on to the next file. Note that the
625 lines are printed automatically. An error occurring during printing is
626 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
627 overrides a B<-n> switch.
629 C<BEGIN> and C<END> blocks may be used to capture control before or after
630 the implicit loop, just as in B<awk>.
634 B<NOTE: Use of -P is strongly discouraged because of its inherent
635 problems, including poor portability.>
637 This option causes your program to be run through the C preprocessor before
638 compilation by Perl. Because both comments and B<cpp> directives begin
639 with the # character, you should avoid starting comments with any words
640 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
642 If you're considering using C<-P>, you might also want to look at the
643 Filter::cpp module from CPAN.
645 The problems of -P include, but are not limited to:
651 The C<#!> line is stripped, so any switches there don't apply.
655 A C<-P> on a C<#!> line doesn't work.
659 B<All> lines that begin with (whitespace and) a C<#> but
660 do not look like cpp commands, are stripped, including anything
661 inside Perl strings, regular expressions, and here-docs .
665 In some platforms the C preprocessor knows too much: it knows about
666 the C++ -style until-end-of-line comments starting with C<"//">.
667 This will cause problems with common Perl constructs like
671 because after -P this will became illegal code
675 The workaround is to use some other quoting separator than C<"/">,
676 like for example C<"!">:
684 It requires not only a working C preprocessor but also a working
685 F<sed>. If not on UNIX, you are probably out of luck on this.
689 Script line numbers are not preserved.
693 The C<-x> does not work with C<-P>.
699 enables rudimentary switch parsing for switches on the command
700 line after the program name but before any filename arguments (or before
701 an argument of B<-->). This means you can have switches with two leading
702 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
703 corresponding variable in the Perl program. The following program
704 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
705 if it is invoked with B<-xyz=abc>.
708 if ($xyz) { print "$xyz\n" }
710 Do note that B<--help> creates the variable ${-help}, which is not compliant
715 makes Perl use the PATH environment variable to search for the
716 program (unless the name of the program contains directory separators).
718 On some platforms, this also makes Perl append suffixes to the
719 filename while searching for it. For example, on Win32 platforms,
720 the ".bat" and ".cmd" suffixes are appended if a lookup for the
721 original name fails, and if the name does not already end in one
722 of those suffixes. If your Perl was compiled with DEBUGGING turned
723 on, using the -Dp switch to Perl shows how the search progresses.
725 Typically this is used to emulate #! startup on platforms that
726 don't support #!. This example works on many platforms that
727 have a shell compatible with Bourne shell:
730 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
731 if $running_under_some_shell;
733 The system ignores the first line and feeds the program to F</bin/sh>,
734 which proceeds to try to execute the Perl program as a shell script.
735 The shell executes the second line as a normal shell command, and thus
736 starts up the Perl interpreter. On some systems $0 doesn't always
737 contain the full pathname, so the B<-S> tells Perl to search for the
738 program if necessary. After Perl locates the program, it parses the
739 lines and ignores them because the variable $running_under_some_shell
740 is never true. If the program will be interpreted by csh, you will need
741 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
742 embedded spaces (and such) in the argument list. To start up sh rather
743 than csh, some systems may have to replace the #! line with a line
744 containing just a colon, which will be politely ignored by Perl. Other
745 systems can't control that, and need a totally devious construct that
746 will work under any of B<csh>, B<sh>, or Perl, such as the following:
748 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
749 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
750 if $running_under_some_shell;
752 If the filename supplied contains directory separators (i.e., is an
753 absolute or relative pathname), and if that file is not found,
754 platforms that append file extensions will do so and try to look
755 for the file with those extensions added, one by one.
757 On DOS-like platforms, if the program does not contain directory
758 separators, it will first be searched for in the current directory
759 before being searched for on the PATH. On Unix platforms, the
760 program will be searched for strictly on the PATH.
764 Like B<-T>, but taint checks will issue warnings rather than fatal
765 errors. These warnings can be controlled normally with C<no warnings
768 B<NOTE: this is not a substitute for -T.> This is meant only to be
769 used as a temporary development aid while securing legacy code:
770 for real production code and for new secure code written from scratch
771 always use the real B<-T>.
775 forces "taint" checks to be turned on so you can test them. Ordinarily
776 these checks are done only when running setuid or setgid. It's a
777 good idea to turn them on explicitly for programs that run on behalf
778 of someone else whom you might not necessarily trust, such as CGI
779 programs or any internet servers you might write in Perl. See
780 L<perlsec> for details. For security reasons, this option must be
781 seen by Perl quite early; usually this means it must appear early
782 on the command line or in the #! line for systems which support
787 This obsolete switch causes Perl to dump core after compiling your
788 program. You can then in theory take this core dump and turn it
789 into an executable file by using the B<undump> program (not supplied).
790 This speeds startup at the expense of some disk space (which you
791 can minimize by stripping the executable). (Still, a "hello world"
792 executable comes out to about 200K on my machine.) If you want to
793 execute a portion of your program before dumping, use the dump()
794 operator instead. Note: availability of B<undump> is platform
795 specific and may not be available for a specific port of Perl.
797 This switch has been superseded in favor of the new Perl code
798 generator backends to the compiler. See L<B> and L<B::Bytecode>
803 allows Perl to do unsafe operations. Currently the only "unsafe"
804 operations are the unlinking of directories while running as superuser,
805 and running setuid programs with fatal taint checks turned into
806 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
807 be used along with this option to actually I<generate> the
808 taint-check warnings.
812 prints the version and patchlevel of your perl executable.
816 prints summary of the major perl configuration values and the current
821 Prints to STDOUT the value of the named configuration variable.
826 will provide strong clues about what your MANPATH variable should
827 be set to in order to access the Perl documentation.
831 prints warnings about dubious constructs, such as variable names
832 that are mentioned only once and scalar variables that are used
833 before being set, redefined subroutines, references to undefined
834 filehandles or filehandles opened read-only that you are attempting
835 to write on, values used as a number that doesn't look like numbers,
836 using an array as though it were a scalar, if your subroutines
837 recurse more than 100 deep, and innumerable other things.
839 This switch really just enables the internal C<$^W> variable. You
840 can disable or promote into fatal errors specific warnings using
841 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
842 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
843 facility is also available if you want to manipulate entire classes
844 of warnings; see L<warnings> or L<perllexwarn>.
848 Enables all warnings regardless of C<no warnings> or C<$^W>.
853 Disables all warnings regardless of C<use warnings> or C<$^W>.
856 =item B<-x> I<directory>
858 tells Perl that the program is embedded in a larger chunk of unrelated
859 ASCII text, such as in a mail message. Leading garbage will be
860 discarded until the first line that starts with #! and contains the
861 string "perl". Any meaningful switches on that line will be applied.
862 If a directory name is specified, Perl will switch to that directory
863 before running the program. The B<-x> switch controls only the
864 disposal of leading garbage. The program must be terminated with
865 C<__END__> if there is trailing garbage to be ignored (the program
866 can process any or all of the trailing garbage via the DATA filehandle
877 Used if chdir has no argument.
881 Used if chdir has no argument and HOME is not set.
885 Used in executing subprocesses, and in finding the program if B<-S> is
890 A colon-separated list of directories in which to look for Perl library
891 files before looking in the standard library and the current
892 directory. Any architecture-specific directories under the specified
893 locations are automatically included if they exist. If PERL5LIB is not
894 defined, PERLLIB is used.
896 When running taint checks (either because the program was running setuid
897 or setgid, or the B<-T> switch was used), neither variable is used.
898 The program should instead say:
900 use lib "/my/directory";
904 Command-line options (switches). Switches in this variable are taken
905 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
906 switches are allowed. When running taint checks (because the program
907 was running setuid or setgid, or the B<-T> switch was used), this
908 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
909 enabled, and any subsequent options ignored.
913 A space (or colon) separated list of PerlIO layers. If perl is built
914 to use PerlIO system for IO (the default) these layers effect perl's IO.
916 It is conventional to start layer names with a colon e.g. C<:perlio> to
917 emphasise their similarity to variable "attributes". But the code that parses
918 layer specification strings (which is also used to decode the PERLIO
919 environment variable) treats the colon as a separator.
921 An unset or empty PERLIO is equivalent to C<:stdio>.
923 The list becomes the default for I<all> perl's IO. Consequently only built-in
924 layers can appear in this list, as external layers (such as :encoding()) need
925 IO in order to load them!. See L<"open pragma"|open> for how to add external
926 encodings as defaults.
928 The layers that it makes sense to include in the PERLIO environment
929 variable are summarised below. For more details see L<PerlIO>.
935 Turns I<off> the C<:utf8> flag for the layer below.
936 Unlikely to be useful in global PERLIO environment variable.
940 A layer that implements DOS/Windows like CRLF line endings.
941 On read converts pairs of CR,LF to a single "\n" newline character.
942 On write converts each "\n" to a CR,LF pair.
943 Based on the C<:perlio> layer.
947 A layer which implements "reading" of files by using C<mmap()> to
948 make (whole) file appear in the process's address space, and then
949 using that as PerlIO's "buffer". This I<may> be faster in certain
950 circumstances for large files, and may result in less physical memory
951 use when multiple processes are reading the same file.
953 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
954 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
955 needs extra house-keeping (to extend the file) which negates any advantage.
957 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
961 A from scratch implementation of buffering for PerlIO. Provides fast
962 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
963 and in general attempts to minimize data copying.
965 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
969 Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
970 It makes the stream pass each byte as-is without any translation.
971 In particular CRLF translation, and/or :utf8 intuited from locale
974 Arranges for all accesses go straight to the lowest buffered layer provided
975 by the configration. That is it strips off any layers above that layer.
977 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
978 referred to as a "discipline") is documented as the inverse of the
979 C<:crlf> layer. That is no longer the case - other layers which would
980 alter binary nature of the stream are also disabled. If you want UNIX
981 line endings on a platform that normally does CRLF translation, but still
982 want UTF-8 or encoding defaults the appropriate thing to do is to add
983 C<:perlio> to PERLIO environment variable.
987 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
988 library calls. The layer provides both buffering and IO.
989 Note that C<:stdio> layer does I<not> do CRLF translation even if that
990 is platforms normal behaviour. You will need a C<:crlf> layer above it
995 Lowest level layer which provides basic PerlIO operations in terms of
996 UNIX/POSIX numeric file descriptor calls
997 C<open(), read(), write(), lseek(), close()>
1001 Turns on a flag on the layer below to tell perl that data sent to the
1002 stream should be converted to perl internal "utf8" form and that data from the
1003 stream should be considered as so encoded. On ASCII based platforms the
1004 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
1005 May be useful in PERLIO environment variable to make UTF-8 the
1006 default. (To turn off that behaviour use C<:bytes> layer.)
1010 On Win32 platforms this I<experimental> layer uses native "handle" IO
1011 rather than unix-like numeric file descriptor layer. Known to be
1012 buggy in this release.
1016 On all platforms the default set of layers should give acceptable results.
1018 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1019 Configure is setup to prefer "stdio" implementation if system's library
1020 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1023 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1024 has a number of bugs/mis-features for perl IO which are somewhat
1025 C compiler vendor/version dependent. Using our own C<crlf> layer as
1026 the buffer avoids those issues and makes things more uniform.
1027 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1030 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1031 compiler's numeric file descriptor routines. There is an experimental native
1032 C<win32> layer which is expected to be enhanced and should eventually replace
1037 If set to the name of a file or device then certain operations of PerlIO
1038 sub-system will be logged to that file (opened as append). Typical uses
1041 PERLIO_DEBUG=/dev/tty perl script ...
1043 and Win32 approximate equivalent:
1045 set PERLIO_DEBUG=CON
1051 A colon-separated list of directories in which to look for Perl library
1052 files before looking in the standard library and the current directory.
1053 If PERL5LIB is defined, PERLLIB is not used.
1057 The command used to load the debugger code. The default is:
1059 BEGIN { require 'perl5db.pl' }
1061 =item PERL5SHELL (specific to the Win32 port)
1063 May be set to an alternative shell that perl must use internally for
1064 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1065 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1066 to be space-separated. Precede any character that needs to be protected
1067 (like a space or backslash) with a backslash.
1069 Note that Perl doesn't use COMSPEC for this purpose because
1070 COMSPEC has a high degree of variability among users, leading to
1071 portability concerns. Besides, perl can use a shell that may not be
1072 fit for interactive use, and setting COMSPEC to such a shell may
1073 interfere with the proper functioning of other programs (which usually
1074 look in COMSPEC to find a shell fit for interactive use).
1076 =item PERL_DEBUG_MSTATS
1078 Relevant only if perl is compiled with the malloc included with the perl
1079 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1080 If set, this causes memory statistics to be dumped after execution. If set
1081 to an integer greater than one, also causes memory statistics to be dumped
1084 =item PERL_DESTRUCT_LEVEL
1086 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1087 this controls the behavior of global destruction of objects and other
1088 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1092 If using the C<encoding> pragma without an explicit encoding name, the
1093 PERL_ENCODING environment variable is consulted for an encoding name.
1095 =item PERL_ROOT (specific to the VMS port)
1097 A translation concealed rooted logical name that contains perl and the
1098 logical device for the @INC path on VMS only. Other logical names that
1099 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1100 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1101 L<perlvms> and in F<README.vms> in the Perl source distribution.
1105 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1106 signals behaviour (immediate but unsafe) is restored. If set to
1107 C<safe> the safe (or deferred) signals are used. See L<perlipc>.
1111 Equivalent to the B<-C> command-line switch. Note that this is not
1112 a boolean variable-- setting this to C<"1"> is not the right way to
1113 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1114 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1115 your shell before starting Perl). See the description of the C<-C>
1116 switch for more information.
1118 =item SYS$LOGIN (specific to the VMS port)
1120 Used if chdir has no argument and HOME and LOGDIR are not set.
1124 Perl also has environment variables that control how Perl handles data
1125 specific to particular natural languages. See L<perllocale>.
1127 Apart from these, Perl uses no other environment variables, except
1128 to make them available to the program being executed, and to child
1129 processes. However, programs running setuid would do well to execute
1130 the following lines before doing anything else, just to keep people
1133 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1134 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1135 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};