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1=head1 NAME
2
3perlrun - how to execute the Perl interpreter
4
5=head1 SYNOPSIS
6
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7B<perl> S<[ B<-sTuU> ]>
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...'> ]>
12 S<[ B<-P> ]>
13 S<[ B<-S> ]>
14 S<[ B<-x>[I<dir>] ]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
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17
18=head1 DESCRIPTION
19
20Upon startup, Perl looks for your script in one of the following
21places:
22
23=over 4
24
25=item 1.
26
27Specified line by line via B<-e> switches on the command line.
28
29=item 2.
30
31Contained in the file specified by the first filename on the command line.
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32(Note that systems supporting the #! notation invoke interpreters this
33way. See L<Location of Perl>.)
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34
35=item 3.
36
5f05dabc 37Passed in implicitly via standard input. This works only if there are
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38no filename arguments--to pass arguments to a STDIN script you
39must explicitly specify a "-" for the script name.
40
41=back
42
43With methods 2 and 3, Perl starts parsing the input file from the
44beginning, unless you've specified a B<-x> switch, in which case it
45scans for the first line starting with #! and containing the word
46"perl", and starts there instead. This is useful for running a script
47embedded in a larger message. (In this case you would indicate the end
54310121 48of the script using the C<__END__> token.)
a0d0e21e 49
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50The #! line is always examined for switches as the line is being
51parsed. Thus, if you're on a machine that allows only one argument
52with the #! line, or worse, doesn't even recognize the #! line, you
53still can get consistent switch behavior regardless of how Perl was
54invoked, even if B<-x> was used to find the beginning of the script.
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55
56Because many operating systems silently chop off kernel interpretation of
57the #! line after 32 characters, some switches may be passed in on the
58command line, and some may not; you could even get a "-" without its
59letter, if you're not careful. You probably want to make sure that all
60your switches fall either before or after that 32 character boundary.
61Most switches don't actually care if they're processed redundantly, but
62getting a - instead of a complete switch could cause Perl to try to
63execute standard input instead of your script. And a partial B<-I> switch
64could also cause odd results.
65
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66Some switches do care if they are processed twice, for instance combinations
67of B<-l> and B<-0>. Either put all the switches after the 32 character
68boundary (if applicable), or replace the use of B<-0>I<digits> by
69C<BEGIN{ $/ = "\0digits"; }>.
70
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71Parsing of the #! switches starts wherever "perl" is mentioned in the line.
72The sequences "-*" and "- " are specifically ignored so that you could,
73if you were so inclined, say
74
75 #!/bin/sh -- # -*- perl -*- -p
a3cb178b 76 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
5f05dabc 77 if $running_under_some_shell;
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78
79to let Perl see the B<-p> switch.
80
81If the #! line does not contain the word "perl", the program named after
82the #! is executed instead of the Perl interpreter. This is slightly
83bizarre, but it helps people on machines that don't do #!, because they
84can tell a program that their SHELL is /usr/bin/perl, and Perl will then
85dispatch the program to the correct interpreter for them.
86
87After locating your script, Perl compiles the entire script to an
88internal form. If there are any compilation errors, execution of the
89script is not attempted. (This is unlike the typical shell script,
54310121 90which might run part-way through before finding a syntax error.)
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91
92If the script is syntactically correct, it is executed. If the script
93runs off the end without hitting an exit() or die() operator, an implicit
94C<exit(0)> is provided to indicate successful completion.
95
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96=head2 #! and quoting on non-Unix systems
97
98Unix's #! technique can be simulated on other systems:
99
100=over 4
101
102=item OS/2
103
104Put
105
106 extproc perl -S -your_switches
107
108as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
109`extproc' handling).
110
54310121 111=item MS-DOS
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112
113Create a batch file to run your script, and codify it in
114C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
115distribution for more information).
116
117=item Win95/NT
118
119The Win95/NT installation, when using the Activeware port of Perl,
c8db1d39 120will modify the Registry to associate the F<.pl> extension with the perl
68dc0745 121interpreter. If you install another port of Perl, including the one
4a6725af 122in the Win32 directory of the Perl distribution, then you'll have to
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123modify the Registry yourself. Note that this means you can no
124longer tell the difference between an executable Perl program
125and a Perl library file.
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126
127=item Macintosh
128
10a676f8 129Macintosh perl scripts will have the appropriate Creator and
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130Type, so that double-clicking them will invoke the perl application.
131
132=back
133
134Command-interpreters on non-Unix systems have rather different ideas
135on quoting than Unix shells. You'll need to learn the special
136characters in your command-interpreter (C<*>, C<\> and C<"> are
137common) and how to protect whitespace and these characters to run
138one-liners (see C<-e> below).
139
140On some systems, you may have to change single-quotes to double ones,
141which you must I<NOT> do on Unix or Plan9 systems. You might also
142have to change a single % to a %%.
143
144For example:
145
146 # Unix
147 perl -e 'print "Hello world\n"'
148
54310121 149 # MS-DOS, etc.
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150 perl -e "print \"Hello world\n\""
151
54310121 152 # Macintosh
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153 print "Hello world\n"
154 (then Run "Myscript" or Shift-Command-R)
155
156 # VMS
157 perl -e "print ""Hello world\n"""
158
159The problem is that none of this is reliable: it depends on the command
54310121 160and it is entirely possible neither works. If 4DOS was the command shell, this would
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161probably work better:
162
163 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
164
165CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
166when nobody was looking, but just try to find documentation for its
167quoting rules.
168
54310121 169Under the Macintosh, it depends which environment you are using. The MacPerl
68dc0745 170shell, or MPW, is much like Unix shells in its support for several
54310121 171quoting variants, except that it makes free use of the Macintosh's non-ASCII
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172characters as control characters.
173
174There is no general solution to all of this. It's just a mess.
175
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176=head2 Location of Perl
177
178It may seem obvious to say, but Perl is useful only when users can
179easily find it. When possible, it's good for both B</usr/bin/perl> and
180B</usr/local/bin/perl> to be symlinks to the actual binary. If that
181can't be done, system administrators are strongly encouraged to put
182(symlinks to) perl and its accompanying utilities, such as perldoc, into
183a directory typically found along a user's PATH, or in another obvious
184and convenient place.
185
186In this documentation, C<#!/usr/bin/perl> on the first line of the script
187will stand in for whatever method works on your system.
188
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189=head2 Switches
190
191A single-character switch may be combined with the following switch, if
192any.
193
194 #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
195
196Switches include:
197
198=over 5
199
e0ebc809 200=item B<-0>[I<digits>]
a0d0e21e 201
55497cff 202specifies the input record separator (C<$/>) as an octal number. If there are
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203no digits, the null character is the separator. Other switches may
204precede or follow the digits. For example, if you have a version of
205B<find> which can print filenames terminated by the null character, you
206can say this:
207
208 find . -name '*.bak' -print0 | perl -n0e unlink
209
210The special value 00 will cause Perl to slurp files in paragraph mode.
5f05dabc 211The value 0777 will cause Perl to slurp files whole because there is no
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212legal character with that value.
213
214=item B<-a>
215
216turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
217split command to the @F array is done as the first thing inside the
218implicit while loop produced by the B<-n> or B<-p>.
219
220 perl -ane 'print pop(@F), "\n";'
221
222is equivalent to
223
224 while (<>) {
225 @F = split(' ');
226 print pop(@F), "\n";
227 }
228
229An alternate delimiter may be specified using B<-F>.
230
231=item B<-c>
232
233causes Perl to check the syntax of the script and then exit without
cb1a09d0 234executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
54310121 235because these are considered as occurring outside the execution of
cb1a09d0 236your program.
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237
238=item B<-d>
239
240runs the script under the Perl debugger. See L<perldebug>.
241
e0ebc809 242=item B<-d:>I<foo>
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243
244runs the script under the control of a debugging or tracing module
a77489aa 245installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
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246Devel::DProf profiler. See L<perldebug>.
247
db2ba183 248=item B<-D>I<letters>
a0d0e21e 249
db2ba183 250=item B<-D>I<number>
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251
252sets debugging flags. To watch how it executes your script, use
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253B<-Dtls>. (This works only if debugging is compiled into your
254Perl.) Another nice value is B<-Dx>, which lists your compiled
255syntax tree. And B<-Dr> displays compiled regular expressions. As an
256alternative, specify a number instead of list of letters (e.g., B<-D14> is
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257equivalent to B<-Dtls>):
258
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259 1 p Tokenizing and parsing
260 2 s Stack snapshots
261 4 l Context (loop) stack processing
262 8 t Trace execution
263 16 o Method and overloading resolution
264 32 c String/numeric conversions
265 64 P Print preprocessor command for -P
266 128 m Memory allocation
267 256 f Format processing
268 512 r Regular expression parsing and execution
269 1024 x Syntax tree dump
270 2048 u Tainting checks
8c52afec 271 4096 L Memory leaks (needs C<-DLEAKTEST> when compiling Perl)
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272 8192 H Hash dump -- usurps values()
273 16384 X Scratchpad allocation
274 32768 D Cleaning up
a0d0e21e 275
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276All these flags require C<-DDEBUGGING> when you compile the Perl
277executable. This flag is automatically set if you include C<-g>
278option when C<Configure> asks you about optimizer/debugger flags.
279
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280=item B<-e> I<commandline>
281
54310121 282may be used to enter one line of script.
a0d0e21e 283If B<-e> is given, Perl
54310121 284will not look for a script filename in the argument list.
a0d0e21e 285Multiple B<-e> commands may
4a6725af 286be given to build up a multi-line script.
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287Make sure to use semicolons where you would in a normal program.
288
e0ebc809 289=item B<-F>I<pattern>
a0d0e21e 290
e0ebc809 291specifies the pattern to split on if B<-a> is also in effect. The
5f05dabc 292pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
e0ebc809 293put in single quotes.
a0d0e21e 294
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295=item B<-h>
296
297prints a summary of the options.
298
299=item B<-i>[I<extension>]
a0d0e21e 300
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301specifies that files processed by the C<E<lt>E<gt>> construct are to be
302edited in-place. It does this by renaming the input file, opening the
303output file by the original name, and selecting that output file as the
304default for print() statements. The extension, if supplied, is used to
305modify the name of the old file to make a backup copy, following these
306rules:
307
308If no extension is supplied, no backup is made and the current file is
309overwritten.
310
311If the extension doesn't contain a C<*> then it is appended to the end
312of the current filename as a suffix.
313
314If the extension does contain one or more C<*> characters, then each C<*>
315is replaced with the current filename. In perl terms you could think of
316this as:
317
318 ($old_file_name = $extension) =~ s/\*/$file_name/g;
319
320This allows you to add a prefix to the backup file, instead of (or in
321addition to) a suffix:
322
323 $ perl -pi'bak_*' -e 's/bar/baz/' fileA # backup to 'bak_fileA'
324
325Or even to place backup copies of the original files into another
326directory (provided the directory already exists):
327
328 $ perl -pi'old/*.bak' -e 's/bar/baz/' fileA # backup to 'old/fileA.bak'
329
330From the shell, saying
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331
332 $ perl -p -i.bak -e "s/foo/bar/; ... "
333
334is the same as using the script:
335
336 #!/usr/bin/perl -pi.bak
337 s/foo/bar/;
338
339which is equivalent to
340
341 #!/usr/bin/perl
342 while (<>) {
343 if ($ARGV ne $oldargv) {
344 rename($ARGV, $ARGV . '.bak');
345 open(ARGVOUT, ">$ARGV");
346 select(ARGVOUT);
347 $oldargv = $ARGV;
348 }
349 s/foo/bar/;
350 }
351 continue {
352 print; # this prints to original filename
353 }
354 select(STDOUT);
355
356except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
357know when the filename has changed. It does, however, use ARGVOUT for
358the selected filehandle. Note that STDOUT is restored as the
359default output filehandle after the loop.
360
7b8d334a 361You can use C<eof> without parentheses to locate the end of each input file,
54310121 362in case you want to append to each file, or reset line numbering (see
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363example in L<perlfunc/eof>).
364
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365Finally, note that the B<-i> switch does not impede execution when no
366files are given on the command line. In this case, no backup is made
367(the original file cannot, of course, be determined) and processing
368proceeds from STDIN to STDOUT as might be expected.
369
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370=item B<-I>I<directory>
371
e0ebc809 372Directories specified by B<-I> are prepended to the search path for
1fef88e7 373modules (C<@INC>), and also tells the C preprocessor where to search for
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374include files. The C preprocessor is invoked with B<-P>; by default it
375searches /usr/include and /usr/lib/perl.
a0d0e21e 376
e0ebc809 377=item B<-l>[I<octnum>]
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378
379enables automatic line-ending processing. It has two effects: first,
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380it automatically chomps "C<$/>" (the input record separator) when used
381with B<-n> or B<-p>, and second, it assigns "C<$\>"
382(the output record separator) to have the value of I<octnum> so that
383any print statements will have that separator added back on. If
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384I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
385instance, to trim lines to 80 columns:
386
387 perl -lpe 'substr($_, 80) = ""'
388
389Note that the assignment C<$\ = $/> is done when the switch is processed,
390so the input record separator can be different than the output record
391separator if the B<-l> switch is followed by a B<-0> switch:
392
393 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
394
1fef88e7 395This sets C<$\> to newline and then sets C<$/> to the null character.
a0d0e21e 396
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397=item B<-m>[B<->]I<module>
398
399=item B<-M>[B<->]I<module>
c07a80fd 400
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401=item B<-M>[B<->]I<'module ...'>
402
403=item B<-[mM]>[B<->]I<module=arg[,arg]...>
3c81428c 404
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405C<-m>I<module> executes C<use> I<module> C<();> before executing your
406script.
3c81428c 407
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408C<-M>I<module> executes C<use> I<module> C<;> before executing your
409script. You can use quotes to add extra code after the module name,
410e.g., C<-M'module qw(foo bar)'>.
3c81428c 411
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412If the first character after the C<-M> or C<-m> is a dash (C<->)
413then the 'use' is replaced with 'no'.
414
54310121 415A little builtin syntactic sugar means you can also say
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416C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for
417C<-M'module qw(foo bar)'>. This avoids the need to use quotes when
418importing symbols. The actual code generated by C<-Mmodule=foo,bar> is
419C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
a77489aa 420removes the distinction between C<-m> and C<-M>.
3c81428c 421
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422=item B<-n>
423
424causes Perl to assume the following loop around your script, which
425makes it iterate over filename arguments somewhat like B<sed -n> or
426B<awk>:
427
428 while (<>) {
429 ... # your script goes here
430 }
431
432Note that the lines are not printed by default. See B<-p> to have
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433lines printed. If a file named by an argument cannot be opened for
434some reason, Perl warns you about it, and moves on to the next file.
435
436Here is an efficient way to delete all files older than a week:
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437
438 find . -mtime +7 -print | perl -nle 'unlink;'
439
440This is faster than using the C<-exec> switch of B<find> because you don't
441have to start a process on every filename found.
442
443C<BEGIN> and C<END> blocks may be used to capture control before or after
444the implicit loop, just as in B<awk>.
445
446=item B<-p>
447
448causes Perl to assume the following loop around your script, which
449makes it iterate over filename arguments somewhat like B<sed>:
450
451
452 while (<>) {
453 ... # your script goes here
454 } continue {
08e9d68e 455 print or die "-p destination: $!\n";
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456 }
457
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458If a file named by an argument cannot be opened for some reason, Perl
459warns you about it, and moves on to the next file. Note that the
460lines are printed automatically. An error occuring during printing is
461treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
462overrides a B<-n> switch.
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463
464C<BEGIN> and C<END> blocks may be used to capture control before or after
465the implicit loop, just as in awk.
466
467=item B<-P>
468
469causes your script to be run through the C preprocessor before
5f05dabc 470compilation by Perl. (Because both comments and cpp directives begin
a0d0e21e 471with the # character, you should avoid starting comments with any words
5f05dabc 472recognized by the C preprocessor such as "if", "else", or "define".)
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473
474=item B<-s>
475
476enables some rudimentary switch parsing for switches on the command
477line after the script name but before any filename arguments (or before
478a B<-->). Any switch found there is removed from @ARGV and sets the
479corresponding variable in the Perl script. The following script
480prints "true" if and only if the script is invoked with a B<-xyz> switch.
481
482 #!/usr/bin/perl -s
483 if ($xyz) { print "true\n"; }
484
485=item B<-S>
486
487makes Perl use the PATH environment variable to search for the
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488script (unless the name of the script contains directory separators).
489On some platforms, this also makes Perl append suffixes to the
490filename while searching for it. For example, on Win32 platforms,
491the ".bat" and ".cmd" suffixes are appended if a lookup for the
492original name fails, and if the name does not already end in one
493of those suffixes. If your Perl was compiled with DEBUGGING turned
494on, using the -Dp switch to Perl shows how the search progresses.
495
a3cb178b 496If the filename supplied contains directory separators (i.e. it is an
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497absolute or relative pathname), and if the file is not found,
498platforms that append file extensions will do so and try to look
499for the file with those extensions added, one by one.
500
501On DOS-like platforms, if the script does not contain directory
502separators, it will first be searched for in the current directory
503before being searched for on the PATH. On Unix platforms, the
504script will be searched for strictly on the PATH.
505
506Typically this is used to emulate #! startup on platforms that
507don't support #!. This example works on many platforms that
508have a shell compatible with Bourne shell:
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509
510 #!/usr/bin/perl
a3cb178b 511 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
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512 if $running_under_some_shell;
513
514The system ignores the first line and feeds the script to /bin/sh,
515which proceeds to try to execute the Perl script as a shell script.
516The shell executes the second line as a normal shell command, and thus
517starts up the Perl interpreter. On some systems $0 doesn't always
518contain the full pathname, so the B<-S> tells Perl to search for the
519script if necessary. After Perl locates the script, it parses the
520lines and ignores them because the variable $running_under_some_shell
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521is never true. If the script will be interpreted by csh, you will need
522to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
523embedded spaces (and such) in the argument list. To start up sh rather
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524than csh, some systems may have to replace the #! line with a line
525containing just a colon, which will be politely ignored by Perl. Other
526systems can't control that, and need a totally devious construct that
5f05dabc 527will work under any of csh, sh, or Perl, such as the following:
a0d0e21e 528
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529 eval '(exit $?0)' && eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
530 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
5f05dabc 531 if $running_under_some_shell;
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532
533=item B<-T>
534
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535forces "taint" checks to be turned on so you can test them. Ordinarily
536these checks are done only when running setuid or setgid. It's a good
537idea to turn them on explicitly for programs run on another's behalf,
538such as CGI programs. See L<perlsec>. Note that (for security reasons)
539this option must be seen by Perl quite early; usually this means it must
540appear early on the command line or in the #! line (for systems which
541support that).
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542
543=item B<-u>
544
545causes Perl to dump core after compiling your script. You can then
5a964f20 546in theory take this core dump and turn it into an executable file by using the
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547B<undump> program (not supplied). This speeds startup at the expense of
548some disk space (which you can minimize by stripping the executable).
549(Still, a "hello world" executable comes out to about 200K on my
550machine.) If you want to execute a portion of your script before dumping,
551use the dump() operator instead. Note: availability of B<undump> is
552platform specific and may not be available for a specific port of
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553Perl. It has been superseded by the new perl-to-C compiler, which is more
554portable, even though it's still only considered beta.
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555
556=item B<-U>
557
558allows Perl to do unsafe operations. Currently the only "unsafe"
559operations are the unlinking of directories while running as superuser,
560and running setuid programs with fatal taint checks turned into
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561warnings. Note that the B<-w> switch (or the C<$^W> variable) must
562be used along with this option to actually B<generate> the
563taint-check warnings.
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564
565=item B<-v>
566
567prints the version and patchlevel of your Perl executable.
568
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569=item B<-V>
570
571prints summary of the major perl configuration values and the current
572value of @INC.
573
e0ebc809 574=item B<-V:>I<name>
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575
576Prints to STDOUT the value of the named configuration variable.
577
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578=item B<-w>
579
049cd8b0 580prints warnings about variable names that are mentioned only once, and
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581scalar variables that are used before being set. Also warns about
582redefined subroutines, and references to undefined filehandles or
5f05dabc 583filehandles opened read-only that you are attempting to write on. Also
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584warns you if you use values as a number that doesn't look like numbers,
585using an array as though it were a scalar, if your subroutines recurse
586more than 100 deep, and innumerable other things.
587
588You can disable specific warnings using C<__WARN__> hooks, as described
589in L<perlvar> and L<perlfunc/warn>. See also L<perldiag> and L<perltrap>.
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590
591=item B<-x> I<directory>
592
593tells Perl that the script is embedded in a message. Leading
594garbage will be discarded until the first line that starts with #! and
595contains the string "perl". Any meaningful switches on that line will
ff0cee69 596be applied. If a directory name is specified, Perl will switch to
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597that directory before running the script. The B<-x> switch controls
598only the disposal of leading garbage. The script must be
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599terminated with C<__END__> if there is trailing garbage to be ignored (the
600script can process any or all of the trailing garbage via the DATA
601filehandle if desired).
602
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603=back
604
605=head1 ENVIRONMENT
606
607=over 12
608
609=item HOME
610
611Used if chdir has no argument.
612
613=item LOGDIR
614
615Used if chdir has no argument and HOME is not set.
616
617=item PATH
618
619Used in executing subprocesses, and in finding the script if B<-S> is
620used.
621
622=item PERL5LIB
623
624A colon-separated list of directories in which to look for Perl library
625files before looking in the standard library and the current
626directory. If PERL5LIB is not defined, PERLLIB is used. When running
627taint checks (because the script was running setuid or setgid, or the
628B<-T> switch was used), neither variable is used. The script should
629instead say
630
631 use lib "/my/directory";
632
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633=item PERL5OPT
634
635Command-line options (switches). Switches in this variable are taken
636as if they were on every Perl command line. Only the B<-[DIMUdmw]>
637switches are allowed. When running taint checks (because the script
638was running setuid or setgid, or the B<-T> switch was used), this
639variable is ignored.
640
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641=item PERLLIB
642
643A colon-separated list of directories in which to look for Perl library
644files before looking in the standard library and the current directory.
645If PERL5LIB is defined, PERLLIB is not used.
646
647=item PERL5DB
648
649The command used to load the debugger code. The default is:
650
651 BEGIN { require 'perl5db.pl' }
652
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653=item PERL5SHELL (specific to WIN32 port)
654
655May be set to an alternative shell that perl must use internally for
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656executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
657on WindowsNT and C<command.com /c> on Windows95. The value is considered
658to be space delimited. Precede any character that needs to be protected
659(like a space or backslash) with a backslash.
660
661Note that Perl doesn't use COMSPEC for this purpose because
662COMSPEC has a high degree of variability among users, leading to
663portability concerns. Besides, perl can use a shell that may not be
664fit for interactive use, and setting COMSPEC to such a shell may
665interfere with the proper functioning of other programs (which usually
666look in COMSPEC to find a shell fit for interactive use).
174c211a 667
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668=item PERL_DEBUG_MSTATS
669
67ce8856 670Relevant only if perl is compiled with the malloc included with the perl
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671distribution (that is, if C<perl -V:d_mymalloc> is 'define').
672If set, this causes memory statistics to be dumped after execution. If set
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673to an integer greater than one, also causes memory statistics to be dumped
674after compilation.
675
676=item PERL_DESTRUCT_LEVEL
677
678Relevant only if your perl executable was built with B<-DDEBUGGING>,
679this controls the behavior of global destruction of objects and other
680references.
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681
682=back
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683
684Perl also has environment variables that control how Perl handles data
685specific to particular natural languages. See L<perllocale>.
686
687Apart from these, Perl uses no other environment variables, except
688to make them available to the script being executed, and to child
689processes. However, scripts running setuid would do well to execute
690the following lines before doing anything else, just to keep people
691honest:
692
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693 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
694 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
c90c0ff4 695 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
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