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1=head1 NAME
2
3perlrun - how to execute the Perl interpreter
4
5=head1 SYNOPSIS
6
672fde27 7B<perl> S<[ B<-sTtuUWX> ]>
e0ebc809 8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
2cbb2ee1 9 S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>
f2095865 10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>
df451b2a 11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
aefc56c5 12 S<[ B<-A>[I<module>][=I<assertions>] ]>
c630fe62 13 S<[ B<-C [I<number/list>] >]>
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14 S<[ B<-P> ]>
15 S<[ B<-S> ]>
16 S<[ B<-x>[I<dir>] ]>
17 S<[ B<-i>[I<extension>] ]>
18 S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
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19
20=head1 DESCRIPTION
21
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22The normal way to run a Perl program is by making it directly
23executable, or else by passing the name of the source file as an
24argument on the command line. (An interactive Perl environment
25is also possible--see L<perldebug> for details on how to do that.)
26Upon startup, Perl looks for your program in one of the following
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27places:
28
29=over 4
30
31=item 1.
32
33Specified line by line via B<-e> switches on the command line.
34
35=item 2.
36
37Contained in the file specified by the first filename on the command line.
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38(Note that systems supporting the #! notation invoke interpreters this
39way. See L<Location of Perl>.)
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40
41=item 3.
42
5f05dabc 43Passed in implicitly via standard input. This works only if there are
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44no filename arguments--to pass arguments to a STDIN-read program you
45must explicitly specify a "-" for the program name.
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46
47=back
48
49With methods 2 and 3, Perl starts parsing the input file from the
50beginning, unless you've specified a B<-x> switch, in which case it
51scans for the first line starting with #! and containing the word
19799a22 52"perl", and starts there instead. This is useful for running a program
a0d0e21e 53embedded in a larger message. (In this case you would indicate the end
19799a22 54of the program using the C<__END__> token.)
a0d0e21e 55
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56The #! line is always examined for switches as the line is being
57parsed. Thus, if you're on a machine that allows only one argument
58with the #! line, or worse, doesn't even recognize the #! line, you
59still can get consistent switch behavior regardless of how Perl was
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60invoked, even if B<-x> was used to find the beginning of the program.
61
62Because historically some operating systems silently chopped off
63kernel interpretation of the #! line after 32 characters, some
64switches may be passed in on the command line, and some may not;
65you could even get a "-" without its letter, if you're not careful.
66You probably want to make sure that all your switches fall either
67before or after that 32-character boundary. Most switches don't
68actually care if they're processed redundantly, but getting a "-"
69instead of a complete switch could cause Perl to try to execute
70standard input instead of your program. And a partial B<-I> switch
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71could also cause odd results.
72
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73Some switches do care if they are processed twice, for instance
74combinations of B<-l> and B<-0>. Either put all the switches after
75the 32-character boundary (if applicable), or replace the use of
76B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
fb73857a 77
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78Parsing of the #! switches starts wherever "perl" is mentioned in the line.
79The sequences "-*" and "- " are specifically ignored so that you could,
80if you were so inclined, say
81
82 #!/bin/sh -- # -*- perl -*- -p
19799a22 83 eval 'exec perl -wS $0 ${1+"$@"}'
5f05dabc 84 if $running_under_some_shell;
a0d0e21e 85
44a4342c 86to let Perl see the B<-p> switch.
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87
88A similar trick involves the B<env> program, if you have it.
89
90 #!/usr/bin/env perl
91
92The examples above use a relative path to the perl interpreter,
93getting whatever version is first in the user's path. If you want
94a specific version of Perl, say, perl5.005_57, you should place
95that directly in the #! line's path.
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96
97If the #! line does not contain the word "perl", the program named after
98the #! is executed instead of the Perl interpreter. This is slightly
99bizarre, but it helps people on machines that don't do #!, because they
19799a22 100can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
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101dispatch the program to the correct interpreter for them.
102
19799a22 103After locating your program, Perl compiles the entire program to an
a0d0e21e 104internal form. If there are any compilation errors, execution of the
19799a22 105program is not attempted. (This is unlike the typical shell script,
54310121 106which might run part-way through before finding a syntax error.)
a0d0e21e 107
19799a22 108If the program is syntactically correct, it is executed. If the program
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109runs off the end without hitting an exit() or die() operator, an implicit
110C<exit(0)> is provided to indicate successful completion.
111
68dc0745 112=head2 #! and quoting on non-Unix systems
d74e8afc 113X<hashbang> X<#!>
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114
115Unix's #! technique can be simulated on other systems:
116
117=over 4
118
119=item OS/2
120
121Put
122
123 extproc perl -S -your_switches
124
19799a22 125as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
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126`extproc' handling).
127
54310121 128=item MS-DOS
68dc0745 129
19799a22 130Create a batch file to run your program, and codify it in
fd1adc71 131C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
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132distribution for more information).
133
134=item Win95/NT
135
6c6a61e2 136The Win95/NT installation, when using the ActiveState installer for Perl,
c8db1d39 137will modify the Registry to associate the F<.pl> extension with the perl
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138interpreter. If you install Perl by other means (including building from
139the sources), you may have to modify the Registry yourself. Note that
140this means you can no longer tell the difference between an executable
141Perl program and a Perl library file.
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142
143=item Macintosh
144
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145Under "Classic" MacOS, a perl program will have the appropriate Creator and
146Type, so that double-clicking them will invoke the MacPerl application.
147Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
148Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
68dc0745 149
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150=item VMS
151
152Put
153
154 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
155 $ exit++ + ++$status != 0 and $exit = $status = undef;
156
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157at the top of your program, where B<-mysw> are any command line switches you
158want to pass to Perl. You can now invoke the program directly, by saying
159C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
160via F<DCL$PATH> by just using the name of the program).
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161
162This incantation is a bit much to remember, but Perl will display it for
163you if you say C<perl "-V:startperl">.
164
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165=back
166
167Command-interpreters on non-Unix systems have rather different ideas
168on quoting than Unix shells. You'll need to learn the special
169characters in your command-interpreter (C<*>, C<\> and C<"> are
170common) and how to protect whitespace and these characters to run
19799a22 171one-liners (see B<-e> below).
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172
173On some systems, you may have to change single-quotes to double ones,
e6f03d26 174which you must I<not> do on Unix or Plan 9 systems. You might also
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175have to change a single % to a %%.
176
177For example:
178
179 # Unix
180 perl -e 'print "Hello world\n"'
181
54310121 182 # MS-DOS, etc.
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183 perl -e "print \"Hello world\n\""
184
54310121 185 # Macintosh
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186 print "Hello world\n"
187 (then Run "Myscript" or Shift-Command-R)
188
189 # VMS
190 perl -e "print ""Hello world\n"""
191
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192The problem is that none of this is reliable: it depends on the
193command and it is entirely possible neither works. If B<4DOS> were
194the command shell, this would probably work better:
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195
196 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
197
19799a22 198B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
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199when nobody was looking, but just try to find documentation for its
200quoting rules.
201
54310121 202Under the Macintosh, it depends which environment you are using. The MacPerl
68dc0745 203shell, or MPW, is much like Unix shells in its support for several
54310121 204quoting variants, except that it makes free use of the Macintosh's non-ASCII
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205characters as control characters.
206
207There is no general solution to all of this. It's just a mess.
208
a3cb178b 209=head2 Location of Perl
d74e8afc 210X<perl, location of interpreter>
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211
212It may seem obvious to say, but Perl is useful only when users can
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213easily find it. When possible, it's good for both F</usr/bin/perl>
214and F</usr/local/bin/perl> to be symlinks to the actual binary. If
215that can't be done, system administrators are strongly encouraged
216to put (symlinks to) perl and its accompanying utilities into a
217directory typically found along a user's PATH, or in some other
218obvious and convenient place.
219
220In this documentation, C<#!/usr/bin/perl> on the first line of the program
221will stand in for whatever method works on your system. You are
222advised to use a specific path if you care about a specific version.
a3cb178b 223
19799a22 224 #!/usr/local/bin/perl5.00554
a3cb178b 225
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226or if you just want to be running at least version, place a statement
227like this at the top of your program:
a0d0e21e 228
19799a22 229 use 5.005_54;
a0d0e21e 230
19799a22 231=head2 Command Switches
d74e8afc 232X<perl, command switches> X<command switches>
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233
234As with all standard commands, a single-character switch may be
235clustered with the following switch, if any.
236
237 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
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238
239Switches include:
240
241=over 5
242
f2095865 243=item B<-0>[I<octal/hexadecimal>]
d74e8afc 244X<-0> X<$/>
a0d0e21e 245
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246specifies the input record separator (C<$/>) as an octal or
247hexadecimal number. If there are no digits, the null character is the
248separator. Other switches may precede or follow the digits. For
249example, if you have a version of B<find> which can print filenames
250terminated by the null character, you can say this:
a0d0e21e 251
19799a22 252 find . -name '*.orig' -print0 | perl -n0e unlink
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253
254The special value 00 will cause Perl to slurp files in paragraph mode.
5f05dabc 255The value 0777 will cause Perl to slurp files whole because there is no
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256legal byte with that value.
257
258If you want to specify any Unicode character, use the hexadecimal
259format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
260(This means that you cannot use the C<-x> with a directory name that
261consists of hexadecimal digits.)
a0d0e21e 262
aefc56c5 263=item B<-A[I<module>][=I<assertions>]>
d74e8afc 264X<-A>
702815ca 265
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266Activates the assertions given after the equal sign as a comma-separated
267list of assertion names or regular expressions. If no assertion name
268is given, activates all assertions.
269
270The module L<assertions::activate> is used by default to activate the
271selected assertions. An alternate module may be specified including
272its name between the switch and the equal sign.
273
274See L<assertions> and L<assertions::activate>.
702815ca 275
a0d0e21e 276=item B<-a>
d74e8afc 277X<-a> X<autosplit>
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278
279turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
280split command to the @F array is done as the first thing inside the
281implicit while loop produced by the B<-n> or B<-p>.
282
283 perl -ane 'print pop(@F), "\n";'
284
285is equivalent to
286
287 while (<>) {
288 @F = split(' ');
289 print pop(@F), "\n";
290 }
291
292An alternate delimiter may be specified using B<-F>.
293
a05d7ebb 294=item B<-C [I<number/list>]>
d74e8afc 295X<-C>
46487f74 296
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297The C<-C> flag controls some Unicode of the Perl Unicode features.
298
299As of 5.8.1, the C<-C> can be followed either by a number or a list
f3f8427d 300of option letters. The letters, their numeric values, and effects
8aa8f774 301are as follows; listing the letters is equal to summing the numbers.
9f21530f 302
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303 I 1 STDIN is assumed to be in UTF-8
304 O 2 STDOUT will be in UTF-8
305 E 4 STDERR will be in UTF-8
306 S 7 I + O + E
307 i 8 UTF-8 is the default PerlIO layer for input streams
308 o 16 UTF-8 is the default PerlIO layer for output streams
309 D 24 i + o
310 A 32 the @ARGV elements are expected to be strings encoded
311 in UTF-8
312 L 64 normally the "IOEioA" are unconditional,
313 the L makes them conditional on the locale environment
314 variables (the LC_ALL, LC_TYPE, and LANG, in the order
315 of decreasing precedence) -- if the variables indicate
316 UTF-8, then the selected "IOEioA" are in effect
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317
318For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
319STDOUT and STDERR. Repeating letters is just redundant, not cumulative
320nor toggling.
a05d7ebb 321
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322The C<io> options mean that any subsequent open() (or similar I/O
323operations) will have the C<:utf8> PerlIO layer implicitly applied
324to them, in other words, UTF-8 is expected from any input stream,
325and UTF-8 is produced to any output stream. This is just the default,
326with explicit layers in open() and with binmode() one can manipulate
327streams as usual.
328
8aa8f774 329C<-C> on its own (not followed by any number or option list), or the
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330empty string C<""> for the C<PERL_UNICODE> environment variable, has the
331same effect as C<-CSDL>. In other words, the standard I/O handles and
332the default C<open()> layer are UTF-8-fied B<but> only if the locale
333environment variables indicate a UTF-8 locale. This behaviour follows
334the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
a05d7ebb 335
47427c4e 336You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
5b4f334e 337disable all the above Unicode features.
fde18df1 338
8aa8f774 339The read-only magic variable C<${^UNICODE}> reflects the numeric value
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340of this setting. This is variable is set during Perl startup and is
341thereafter read-only. If you want runtime effects, use the three-arg
2307c6d0 342open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
ab9e1bb7 343and the C<open> pragma (see L<open>).
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344
345(In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
346that enabled the use of Unicode-aware "wide system call" Win32 APIs.
347This feature was practically unused, however, and the command line
348switch was therefore "recycled".)
46487f74 349
a0d0e21e 350=item B<-c>
d74e8afc 351X<-c>
a0d0e21e 352
19799a22 353causes Perl to check the syntax of the program and then exit without
7d30b5c4 354executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
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355C<use> blocks, because these are considered as occurring outside the
356execution of your program. C<INIT> and C<END> blocks, however, will
357be skipped.
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358
359=item B<-d>
d74e8afc 360X<-d> X<-dt>
a0d0e21e 361
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362=item B<-dt>
363
19799a22 364runs the program under the Perl debugger. See L<perldebug>.
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365If B<t> is specified, it indicates to the debugger that threads
366will be used in the code being debugged.
a0d0e21e 367
70c94a19 368=item B<-d:>I<foo[=bar,baz]>
d74e8afc 369X<-d> X<-dt>
3c81428c 370
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371=item B<-dt:>I<foo[=bar,baz]>
372
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373runs the program under the control of a debugging, profiling, or
374tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
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375the program using the Devel::DProf profiler. As with the B<-M>
376flag, options may be passed to the Devel::foo package where they
377will be received and interpreted by the Devel::foo::import routine.
378The comma-separated list of options must follow a C<=> character.
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379If B<t> is specified, it indicates to the debugger that threads
380will be used in the code being debugged.
70c94a19 381See L<perldebug>.
3c81428c 382
db2ba183 383=item B<-D>I<letters>
d74e8afc 384X<-D> X<DEBUGGING> X<-DDEBUGGING>
a0d0e21e 385
db2ba183 386=item B<-D>I<number>
a0d0e21e 387
19799a22 388sets debugging flags. To watch how it executes your program, use
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389B<-Dtls>. (This works only if debugging is compiled into your
390Perl.) Another nice value is B<-Dx>, which lists your compiled
4197b13f 391syntax tree. And B<-Dr> displays compiled regular expressions;
44a4342c 392the format of the output is explained in L<perldebguts>.
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393
394As an alternative, specify a number instead of list of letters (e.g.,
395B<-D14> is equivalent to B<-Dtls>):
a0d0e21e 396
9388183f 397 1 p Tokenizing and parsing (with v, displays parse stack)
3679267a 398 2 s Stack snapshots (with v, displays all stacks)
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399 4 l Context (loop) stack processing
400 8 t Trace execution
401 16 o Method and overloading resolution
402 32 c String/numeric conversions
1045810a 403 64 P Print profiling info, preprocessor command for -P, source file input state
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404 128 m Memory allocation
405 256 f Format processing
406 512 r Regular expression parsing and execution
407 1024 x Syntax tree dump
408 2048 u Tainting checks
7bab3ede 409 4096 (Obsolete, previously used for LEAKTEST)
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410 8192 H Hash dump -- usurps values()
411 16384 X Scratchpad allocation
412 32768 D Cleaning up
8b73bbec 413 65536 S Thread synchronization
607df283 414 131072 T Tokenising
04932ac8 415 262144 R Include reference counts of dumped variables (eg when using -Ds)
1045810a 416 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
d6721266 417 1048576 v Verbose: use in conjunction with other flags
46187eeb 418 2097152 C Copy On Write
ecae49c0 419 4194304 A Consistency checks on internal structures
3679267a 420 8388608 q quiet - currently only suppresses the "EXECUTING" message
a0d0e21e 421
19799a22 422All these flags require B<-DDEBUGGING> when you compile the Perl
1045810a 423executable (but see L<Devel::Peek>, L<re> which may change this).
44a4342c 424See the F<INSTALL> file in the Perl source distribution
19799a22 425for how to do this. This flag is automatically set if you include B<-g>
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426option when C<Configure> asks you about optimizer/debugger flags.
427
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428If you're just trying to get a print out of each line of Perl code
429as it executes, the way that C<sh -x> provides for shell scripts,
44a4342c 430you can't use Perl's B<-D> switch. Instead do this
19799a22 431
c406981e 432 # If you have "env" utility
fdac53cd 433 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
c406981e 434
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435 # Bourne shell syntax
436 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
437
438 # csh syntax
439 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
440
441See L<perldebug> for details and variations.
442
a0d0e21e 443=item B<-e> I<commandline>
d74e8afc 444X<-e>
a0d0e21e 445
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446may be used to enter one line of program. If B<-e> is given, Perl
447will not look for a filename in the argument list. Multiple B<-e>
448commands may be given to build up a multi-line script. Make sure
449to use semicolons where you would in a normal program.
a0d0e21e 450
20ef40cf 451=item B<-f>
d74e8afc 452X<-f>
20ef40cf 453
4a42f219 454Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
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455
456Perl can be built so that it by default will try to execute
4a42f219 457F<$Config{sitelib}/sitecustomize.pl> at startup. This is a hook that
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458allows the sysadmin to customize how perl behaves. It can for
459instance be used to add entries to the @INC array to make perl find
460modules in non-standard locations.
461
e0ebc809 462=item B<-F>I<pattern>
d74e8afc 463X<-F>
a0d0e21e 464
e0ebc809 465specifies the pattern to split on if B<-a> is also in effect. The
5f05dabc 466pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
d52fe7da 467put in single quotes. You can't use literal whitespace in the pattern.
a0d0e21e 468
e0ebc809 469=item B<-h>
d74e8afc 470X<-h>
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471
472prints a summary of the options.
473
474=item B<-i>[I<extension>]
d74e8afc 475X<-i> X<in-place>
a0d0e21e 476
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477specifies that files processed by the C<E<lt>E<gt>> construct are to be
478edited in-place. It does this by renaming the input file, opening the
479output file by the original name, and selecting that output file as the
480default for print() statements. The extension, if supplied, is used to
481modify the name of the old file to make a backup copy, following these
482rules:
483
484If no extension is supplied, no backup is made and the current file is
485overwritten.
486
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487If the extension doesn't contain a C<*>, then it is appended to the
488end of the current filename as a suffix. If the extension does
489contain one or more C<*> characters, then each C<*> is replaced
490with the current filename. In Perl terms, you could think of this
491as:
2d259d92 492
66606d78 493 ($backup = $extension) =~ s/\*/$file_name/g;
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494
495This allows you to add a prefix to the backup file, instead of (or in
496addition to) a suffix:
497
ddffceb7 498 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
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499
500Or even to place backup copies of the original files into another
501directory (provided the directory already exists):
502
ddffceb7 503 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
2d259d92 504
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505These sets of one-liners are equivalent:
506
507 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
ddffceb7 508 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
66606d78 509
ddffceb7
BD
510 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
511 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
66606d78 512
2d259d92 513From the shell, saying
a0d0e21e 514
19799a22 515 $ perl -p -i.orig -e "s/foo/bar/; ... "
a0d0e21e 516
19799a22 517is the same as using the program:
a0d0e21e 518
19799a22 519 #!/usr/bin/perl -pi.orig
a0d0e21e
LW
520 s/foo/bar/;
521
522which is equivalent to
523
524 #!/usr/bin/perl
19799a22
GS
525 $extension = '.orig';
526 LINE: while (<>) {
a0d0e21e 527 if ($ARGV ne $oldargv) {
66606d78
CK
528 if ($extension !~ /\*/) {
529 $backup = $ARGV . $extension;
530 }
531 else {
532 ($backup = $extension) =~ s/\*/$ARGV/g;
533 }
534 rename($ARGV, $backup);
a0d0e21e
LW
535 open(ARGVOUT, ">$ARGV");
536 select(ARGVOUT);
537 $oldargv = $ARGV;
538 }
539 s/foo/bar/;
540 }
541 continue {
542 print; # this prints to original filename
543 }
544 select(STDOUT);
545
546except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
547know when the filename has changed. It does, however, use ARGVOUT for
66606d78
CK
548the selected filehandle. Note that STDOUT is restored as the default
549output filehandle after the loop.
550
551As shown above, Perl creates the backup file whether or not any output
552is actually changed. So this is just a fancy way to copy files:
553
cd2d1bac 554 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
19799a22 555or
cd2d1bac 556 $ perl -p -i'.orig' -e 1 file1 file2 file3...
66606d78
CK
557
558You can use C<eof> without parentheses to locate the end of each input
559file, in case you want to append to each file, or reset line numbering
560(see example in L<perlfunc/eof>).
561
562If, for a given file, Perl is unable to create the backup file as
563specified in the extension then it will skip that file and continue on
564with the next one (if it exists).
565
19799a22 566For a discussion of issues surrounding file permissions and B<-i>,
cea6626f 567see L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>.
66606d78
CK
568
569You cannot use B<-i> to create directories or to strip extensions from
570files.
a0d0e21e 571
19799a22
GS
572Perl does not expand C<~> in filenames, which is good, since some
573folks use it for their backup files:
a0d0e21e 574
19799a22
GS
575 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
576
a66b22ca 577Note that because B<-i> renames or deletes the original file before
0cb0633f
DM
578creating a new file of the same name, UNIX-style soft and hard links will
579not be preserved.
a66b22ca 580
19799a22 581Finally, the B<-i> switch does not impede execution when no
a2008d6d
GS
582files are given on the command line. In this case, no backup is made
583(the original file cannot, of course, be determined) and processing
584proceeds from STDIN to STDOUT as might be expected.
585
a0d0e21e 586=item B<-I>I<directory>
d74e8afc 587X<-I> X<@INC>
a0d0e21e 588
e0ebc809 589Directories specified by B<-I> are prepended to the search path for
1fef88e7 590modules (C<@INC>), and also tells the C preprocessor where to search for
e0ebc809
PP
591include files. The C preprocessor is invoked with B<-P>; by default it
592searches /usr/include and /usr/lib/perl.
a0d0e21e 593
e0ebc809 594=item B<-l>[I<octnum>]
d74e8afc 595X<-l> X<$/> X<$\>
a0d0e21e 596
19799a22
GS
597enables automatic line-ending processing. It has two separate
598effects. First, it automatically chomps C<$/> (the input record
599separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
600(the output record separator) to have the value of I<octnum> so
601that any print statements will have that separator added back on.
602If I<octnum> is omitted, sets C<$\> to the current value of
603C<$/>. For instance, to trim lines to 80 columns:
a0d0e21e
LW
604
605 perl -lpe 'substr($_, 80) = ""'
606
607Note that the assignment C<$\ = $/> is done when the switch is processed,
608so the input record separator can be different than the output record
609separator if the B<-l> switch is followed by a B<-0> switch:
610
611 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
612
1fef88e7 613This sets C<$\> to newline and then sets C<$/> to the null character.
a0d0e21e 614
e0ebc809 615=item B<-m>[B<->]I<module>
d74e8afc 616X<-m> X<-M>
e0ebc809
PP
617
618=item B<-M>[B<->]I<module>
c07a80fd 619
e0ebc809
PP
620=item B<-M>[B<->]I<'module ...'>
621
622=item B<-[mM]>[B<->]I<module=arg[,arg]...>
3c81428c 623
19799a22
GS
624B<-m>I<module> executes C<use> I<module> C<();> before executing your
625program.
3c81428c 626
19799a22
GS
627B<-M>I<module> executes C<use> I<module> C<;> before executing your
628program. You can use quotes to add extra code after the module name,
629e.g., C<'-Mmodule qw(foo bar)'>.
3c81428c 630
19799a22 631If the first character after the B<-M> or B<-m> is a dash (C<->)
a5f75d66
AD
632then the 'use' is replaced with 'no'.
633
54310121 634A little builtin syntactic sugar means you can also say
19799a22
GS
635B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
636C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
637importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
e0ebc809 638C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
19799a22 639removes the distinction between B<-m> and B<-M>.
3c81428c 640
642d0c2f
RGS
641A consequence of this is that B<-MFoo=number> never does a version check
642(unless C<Foo::import()> itself is set up to do a version check, which
643could happen for example if Foo inherits from Exporter.)
644
a0d0e21e 645=item B<-n>
d74e8afc 646X<-n>
a0d0e21e 647
19799a22 648causes Perl to assume the following loop around your program, which
a0d0e21e
LW
649makes it iterate over filename arguments somewhat like B<sed -n> or
650B<awk>:
651
19799a22 652 LINE:
a0d0e21e 653 while (<>) {
19799a22 654 ... # your program goes here
a0d0e21e
LW
655 }
656
657Note that the lines are not printed by default. See B<-p> to have
08e9d68e 658lines printed. If a file named by an argument cannot be opened for
19799a22 659some reason, Perl warns you about it and moves on to the next file.
08e9d68e 660
fa11829f 661Here is an efficient way to delete all files that haven't been modified for
9976c5c7 662at least a week:
a0d0e21e 663
19799a22 664 find . -mtime +7 -print | perl -nle unlink
a0d0e21e 665
19799a22
GS
666This is faster than using the B<-exec> switch of B<find> because you don't
667have to start a process on every filename found. It does suffer from
668the bug of mishandling newlines in pathnames, which you can fix if
44a4342c 669you follow the example under B<-0>.
a0d0e21e
LW
670
671C<BEGIN> and C<END> blocks may be used to capture control before or after
19799a22 672the implicit program loop, just as in B<awk>.
a0d0e21e
LW
673
674=item B<-p>
d74e8afc 675X<-p>
a0d0e21e 676
19799a22 677causes Perl to assume the following loop around your program, which
a0d0e21e
LW
678makes it iterate over filename arguments somewhat like B<sed>:
679
680
19799a22 681 LINE:
a0d0e21e 682 while (<>) {
19799a22 683 ... # your program goes here
a0d0e21e 684 } continue {
08e9d68e 685 print or die "-p destination: $!\n";
a0d0e21e
LW
686 }
687
08e9d68e
DD
688If a file named by an argument cannot be opened for some reason, Perl
689warns you about it, and moves on to the next file. Note that the
c2611fb3 690lines are printed automatically. An error occurring during printing is
08e9d68e
DD
691treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
692overrides a B<-n> switch.
a0d0e21e
LW
693
694C<BEGIN> and C<END> blocks may be used to capture control before or after
19799a22 695the implicit loop, just as in B<awk>.
a0d0e21e
LW
696
697=item B<-P>
d74e8afc 698X<-P>
a0d0e21e 699
079a94c4
JH
700B<NOTE: Use of -P is strongly discouraged because of its inherent
701problems, including poor portability.>
702
703This option causes your program to be run through the C preprocessor before
efdf3af0 704compilation by Perl. Because both comments and B<cpp> directives begin
a0d0e21e 705with the # character, you should avoid starting comments with any words
efdf3af0 706recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
079a94c4
JH
707
708If you're considering using C<-P>, you might also want to look at the
709Filter::cpp module from CPAN.
710
711The problems of -P include, but are not limited to:
712
713=over 10
714
715=item *
716
717The C<#!> line is stripped, so any switches there don't apply.
718
719=item *
720
721A C<-P> on a C<#!> line doesn't work.
722
723=item *
724
725B<All> lines that begin with (whitespace and) a C<#> but
726do not look like cpp commands, are stripped, including anything
44a4342c 727inside Perl strings, regular expressions, and here-docs .
079a94c4
JH
728
729=item *
730
731In some platforms the C preprocessor knows too much: it knows about
732the C++ -style until-end-of-line comments starting with C<"//">.
efdf3af0
JH
733This will cause problems with common Perl constructs like
734
735 s/foo//;
736
737because after -P this will became illegal code
738
739 s/foo
740
741The workaround is to use some other quoting separator than C<"/">,
742like for example C<"!">:
743
744 s!foo!!;
a0d0e21e 745
079a94c4
JH
746
747
748=item *
749
750It requires not only a working C preprocessor but also a working
751F<sed>. If not on UNIX, you are probably out of luck on this.
752
753=item *
754
755Script line numbers are not preserved.
756
757=item *
758
759The C<-x> does not work with C<-P>.
760
761=back
9a1f07e7 762
a0d0e21e 763=item B<-s>
d74e8afc 764X<-s>
a0d0e21e 765
19799a22
GS
766enables rudimentary switch parsing for switches on the command
767line after the program name but before any filename arguments (or before
3bbcc830
JP
768an argument of B<-->). This means you can have switches with two leading
769dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
19799a22 770corresponding variable in the Perl program. The following program
3c0facb2
GS
771prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
772if it is invoked with B<-xyz=abc>.
a0d0e21e
LW
773
774 #!/usr/bin/perl -s
3c0facb2 775 if ($xyz) { print "$xyz\n" }
a0d0e21e 776
3bbcc830 777Do note that B<--help> creates the variable ${-help}, which is not compliant
50b5b186
SP
778with C<strict refs>. Also, when using this option on a script with
779warnings enabled you may get a lot of spurious "used only once" warnings.
3bbcc830 780
a0d0e21e 781=item B<-S>
d74e8afc 782X<-S>
a0d0e21e
LW
783
784makes Perl use the PATH environment variable to search for the
19799a22
GS
785program (unless the name of the program contains directory separators).
786
2a92aaa0
GS
787On some platforms, this also makes Perl append suffixes to the
788filename while searching for it. For example, on Win32 platforms,
789the ".bat" and ".cmd" suffixes are appended if a lookup for the
790original name fails, and if the name does not already end in one
791of those suffixes. If your Perl was compiled with DEBUGGING turned
792on, using the -Dp switch to Perl shows how the search progresses.
793
fa3aa65a
JC
794Typically this is used to emulate #! startup on platforms that don't
795support #!. Its also convenient when debugging a script that uses #!,
796and is thus normally found by the shell's $PATH search mechanism.
797
798This example works on many platforms that have a shell compatible with
799Bourne shell:
a0d0e21e
LW
800
801 #!/usr/bin/perl
a3cb178b 802 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
a0d0e21e
LW
803 if $running_under_some_shell;
804
19799a22
GS
805The system ignores the first line and feeds the program to F</bin/sh>,
806which proceeds to try to execute the Perl program as a shell script.
a0d0e21e
LW
807The shell executes the second line as a normal shell command, and thus
808starts up the Perl interpreter. On some systems $0 doesn't always
809contain the full pathname, so the B<-S> tells Perl to search for the
19799a22 810program if necessary. After Perl locates the program, it parses the
a0d0e21e 811lines and ignores them because the variable $running_under_some_shell
19799a22 812is never true. If the program will be interpreted by csh, you will need
a3cb178b
GS
813to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
814embedded spaces (and such) in the argument list. To start up sh rather
a0d0e21e
LW
815than csh, some systems may have to replace the #! line with a line
816containing just a colon, which will be politely ignored by Perl. Other
817systems can't control that, and need a totally devious construct that
19799a22 818will work under any of B<csh>, B<sh>, or Perl, such as the following:
a0d0e21e 819
19799a22 820 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
a3cb178b 821 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
5f05dabc 822 if $running_under_some_shell;
a0d0e21e 823
19799a22
GS
824If the filename supplied contains directory separators (i.e., is an
825absolute or relative pathname), and if that file is not found,
826platforms that append file extensions will do so and try to look
827for the file with those extensions added, one by one.
828
829On DOS-like platforms, if the program does not contain directory
830separators, it will first be searched for in the current directory
831before being searched for on the PATH. On Unix platforms, the
832program will be searched for strictly on the PATH.
833
6537fe72 834=item B<-t>
d74e8afc 835X<-t>
6537fe72
MS
836
837Like B<-T>, but taint checks will issue warnings rather than fatal
317ea90d
MS
838errors. These warnings can be controlled normally with C<no warnings
839qw(taint)>.
1dbad523
JH
840
841B<NOTE: this is not a substitute for -T.> This is meant only to be
842used as a temporary development aid while securing legacy code:
843for real production code and for new secure code written from scratch
844always use the real B<-T>.
6537fe72 845
a0d0e21e 846=item B<-T>
d74e8afc 847X<-T>
a0d0e21e 848
a3cb178b 849forces "taint" checks to be turned on so you can test them. Ordinarily
19799a22
GS
850these checks are done only when running setuid or setgid. It's a
851good idea to turn them on explicitly for programs that run on behalf
852of someone else whom you might not necessarily trust, such as CGI
853programs or any internet servers you might write in Perl. See
854L<perlsec> for details. For security reasons, this option must be
855seen by Perl quite early; usually this means it must appear early
856on the command line or in the #! line for systems which support
857that construct.
a0d0e21e
LW
858
859=item B<-u>
d74e8afc 860X<-u>
a0d0e21e 861
19799a22
GS
862This obsolete switch causes Perl to dump core after compiling your
863program. You can then in theory take this core dump and turn it
864into an executable file by using the B<undump> program (not supplied).
865This speeds startup at the expense of some disk space (which you
866can minimize by stripping the executable). (Still, a "hello world"
867executable comes out to about 200K on my machine.) If you want to
868execute a portion of your program before dumping, use the dump()
869operator instead. Note: availability of B<undump> is platform
870specific and may not be available for a specific port of Perl.
871
872This switch has been superseded in favor of the new Perl code
873generator backends to the compiler. See L<B> and L<B::Bytecode>
874for details.
a0d0e21e
LW
875
876=item B<-U>
d74e8afc 877X<-U>
a0d0e21e
LW
878
879allows Perl to do unsafe operations. Currently the only "unsafe"
880operations are the unlinking of directories while running as superuser,
881and running setuid programs with fatal taint checks turned into
19799a22
GS
882warnings. Note that the B<-w> switch (or the C<$^W> variable) must
883be used along with this option to actually I<generate> the
fb73857a 884taint-check warnings.
a0d0e21e
LW
885
886=item B<-v>
d74e8afc 887X<-v>
a0d0e21e 888
19799a22 889prints the version and patchlevel of your perl executable.
a0d0e21e 890
3c81428c 891=item B<-V>
d74e8afc 892X<-V>
3c81428c
PP
893
894prints summary of the major perl configuration values and the current
19799a22 895values of @INC.
3c81428c 896
307dc113 897=item B<-V:>I<configvar>
3c81428c 898
4a305f6a 899Prints to STDOUT the value of the named configuration variable(s),
307dc113
JC
900with multiples when your configvar argument looks like a regex (has
901non-letters). For example:
3c81428c 902
307dc113
JC
903 $ perl -V:libc
904 libc='/lib/libc-2.2.4.so';
4a305f6a
JC
905 $ perl -V:lib.
906 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
907 libc='/lib/libc-2.2.4.so';
908 $ perl -V:lib.*
909 libpth='/usr/local/lib /lib /usr/lib';
910 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
911 lib_ext='.a';
912 libc='/lib/libc-2.2.4.so';
913 libperl='libperl.a';
914 ....
915
916Additionally, extra colons can be used to control formatting. A
917trailing colon suppresses the linefeed and terminator ';', allowing
918you to embed queries into shell commands. (mnemonic: PATH separator
919':'.)
920
921 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
922 compression-vars: zcat='' zip='zip' are here !
923
924A leading colon removes the 'name=' part of the response, this allows
307dc113 925you to map to the name you need. (mnemonic: empty label)
4a305f6a
JC
926
927 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
928 goodvfork=false;
929
930Leading and trailing colons can be used together if you need
931positional parameter values without the names. Note that in the case
932below, the PERL_API params are returned in alphabetical order.
933
934 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
935 building_on 'linux' '5' '1' '9' now
a0d0e21e 936
19799a22 937=item B<-w>
d74e8afc 938X<-w>
774d564b 939
19799a22
GS
940prints warnings about dubious constructs, such as variable names
941that are mentioned only once and scalar variables that are used
942before being set, redefined subroutines, references to undefined
943filehandles or filehandles opened read-only that you are attempting
a4d9c8a6 944to write on, values used as a number that don't look like numbers,
19799a22
GS
945using an array as though it were a scalar, if your subroutines
946recurse more than 100 deep, and innumerable other things.
947
b40da996 948This switch really just enables the internal C<$^W> variable. You
19799a22
GS
949can disable or promote into fatal errors specific warnings using
950C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
951See also L<perldiag> and L<perltrap>. A new, fine-grained warning
952facility is also available if you want to manipulate entire classes
9f1b1f2d 953of warnings; see L<warnings> or L<perllexwarn>.
a0d0e21e 954
0453d815 955=item B<-W>
d74e8afc 956X<-W>
0453d815 957
3c0facb2 958Enables all warnings regardless of C<no warnings> or C<$^W>.
0453d815
PM
959See L<perllexwarn>.
960
961=item B<-X>
d74e8afc 962X<-X>
0453d815 963
3c0facb2 964Disables all warnings regardless of C<use warnings> or C<$^W>.
0453d815
PM
965See L<perllexwarn>.
966
136e4fd6 967=item B<-x>
d74e8afc 968X<-x>
136e4fd6 969
a0d0e21e
LW
970=item B<-x> I<directory>
971
19799a22
GS
972tells Perl that the program is embedded in a larger chunk of unrelated
973ASCII text, such as in a mail message. Leading garbage will be
974discarded until the first line that starts with #! and contains the
975string "perl". Any meaningful switches on that line will be applied.
976If a directory name is specified, Perl will switch to that directory
977before running the program. The B<-x> switch controls only the
978disposal of leading garbage. The program must be terminated with
979C<__END__> if there is trailing garbage to be ignored (the program
980can process any or all of the trailing garbage via the DATA filehandle
981if desired).
a0d0e21e 982
1e422769
PP
983=back
984
985=head1 ENVIRONMENT
d74e8afc 986X<perl, environment variables>
1e422769
PP
987
988=over 12
989
990=item HOME
d74e8afc 991X<HOME>
1e422769
PP
992
993Used if chdir has no argument.
994
995=item LOGDIR
d74e8afc 996X<LOGDIR>
1e422769
PP
997
998Used if chdir has no argument and HOME is not set.
999
1000=item PATH
d74e8afc 1001X<PATH>
1e422769 1002
19799a22 1003Used in executing subprocesses, and in finding the program if B<-S> is
1e422769
PP
1004used.
1005
1006=item PERL5LIB
d74e8afc 1007X<PERL5LIB>
1e422769 1008
48b971ca 1009A list of directories in which to look for Perl library
1e422769 1010files before looking in the standard library and the current
951ba7fe
GS
1011directory. Any architecture-specific directories under the specified
1012locations are automatically included if they exist. If PERL5LIB is not
48b971ca
RGS
1013defined, PERLLIB is used. Directories are separated (like in PATH) by
1014a colon on unixish platforms and by a semicolon on Windows (the proper
1015path separator being given by the command C<perl -V:path_sep>).
951ba7fe
GS
1016
1017When running taint checks (either because the program was running setuid
1018or setgid, or the B<-T> switch was used), neither variable is used.
1019The program should instead say:
1e422769
PP
1020
1021 use lib "/my/directory";
1022
54310121 1023=item PERL5OPT
d74e8afc 1024X<PERL5OPT>
54310121
PP
1025
1026Command-line options (switches). Switches in this variable are taken
e4af53b0 1027as if they were on every Perl command line. Only the B<-[CDIMUdmtwA]>
19799a22 1028switches are allowed. When running taint checks (because the program
54310121 1029was running setuid or setgid, or the B<-T> switch was used), this
74288ac8
GS
1030variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
1031enabled, and any subsequent options ignored.
54310121 1032
16537909 1033=item PERLIO
d74e8afc 1034X<PERLIO>
16537909 1035
44a4342c 1036A space (or colon) separated list of PerlIO layers. If perl is built
03d9e98a 1037to use PerlIO system for IO (the default) these layers effect perl's IO.
44a4342c
NIS
1038
1039It is conventional to start layer names with a colon e.g. C<:perlio> to
1040emphasise their similarity to variable "attributes". But the code that parses
1041layer specification strings (which is also used to decode the PERLIO
1042environment variable) treats the colon as a separator.
1043
3b0db4f9
JH
1044An unset or empty PERLIO is equivalent to C<:stdio>.
1045
44a4342c
NIS
1046The list becomes the default for I<all> perl's IO. Consequently only built-in
1047layers can appear in this list, as external layers (such as :encoding()) need
1048IO in order to load them!. See L<"open pragma"|open> for how to add external
1049encodings as defaults.
1050
1051The layers that it makes sense to include in the PERLIO environment
3d897973 1052variable are briefly summarised below. For more details see L<PerlIO>.
16537909
JH
1053
1054=over 8
1055
1056=item :bytes
d74e8afc 1057X<:bytes>
16537909 1058
18aba96f
JH
1059A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
1060Unlikely to be useful on its own in the global PERLIO environment variable.
1061You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
16537909
JH
1062
1063=item :crlf
d74e8afc 1064X<:crlf>
16537909 1065
3d897973
IT
1066A layer which does CRLF to "\n" translation distinguishing "text" and
1067"binary" files in the manner of MS-DOS and similar operating systems.
1068(It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1069as being an end-of-file marker.)
44a4342c
NIS
1070
1071=item :mmap
d74e8afc 1072X<:mmap>
44a4342c
NIS
1073
1074A layer which implements "reading" of files by using C<mmap()> to
1075make (whole) file appear in the process's address space, and then
3d897973 1076using that as PerlIO's "buffer".
16537909 1077
44a4342c 1078=item :perlio
d74e8afc 1079X<:perlio>
16537909 1080
3d897973
IT
1081This is a re-implementation of "stdio-like" buffering written as a
1082PerlIO "layer". As such it will call whatever layer is below it for
1083its operations (typically C<:unix>).
16537909 1084
18aba96f 1085=item :pop
d74e8afc 1086X<:pop>
18aba96f
JH
1087
1088An experimental pseudolayer that removes the topmost layer.
3d897973 1089Use with the same care as is reserved for nitroglycerin.
18aba96f 1090
44a4342c 1091=item :raw
d74e8afc 1092X<:raw>
16537909 1093
136e4fd6 1094A pseudolayer that manipulates other layers. Applying the C<:raw>
18aba96f
JH
1095layer is equivalent to calling C<binmode($fh)>. It makes the stream
1096pass each byte as-is without any translation. In particular CRLF
1097translation, and/or :utf8 intuited from locale are disabled.
1cbfc93d 1098
3d897973
IT
1099Unlike in the earlier versions of Perl C<:raw> is I<not>
1100just the inverse of C<:crlf> - other layers which would affect the
1101binary nature of the stream are also removed or disabled.
16537909 1102
44a4342c 1103=item :stdio
d74e8afc 1104X<:stdio>
44a4342c
NIS
1105
1106This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1107library calls. The layer provides both buffering and IO.
1108Note that C<:stdio> layer does I<not> do CRLF translation even if that
1109is platforms normal behaviour. You will need a C<:crlf> layer above it
1110to do that.
1111
1112=item :unix
d74e8afc 1113X<:unix>
44a4342c 1114
3d897973 1115Low level layer which calls C<read>, C<write> and C<lseek> etc.
16537909
JH
1116
1117=item :utf8
d74e8afc 1118X<:utf8>
16537909 1119
18aba96f 1120A pseudolayer that turns on a flag on the layer below to tell perl
3d897973
IT
1121that output should be in utf8 and that input should be regarded as
1122already in utf8 form. May be useful in PERLIO environment
1123variable to make UTF-8 the default. (To turn off that behaviour
1124use C<:bytes> layer.)
44a4342c
NIS
1125
1126=item :win32
d74e8afc 1127X<:win32>
44a4342c 1128
ab4f7683 1129On Win32 platforms this I<experimental> layer uses native "handle" IO
44a4342c
NIS
1130rather than unix-like numeric file descriptor layer. Known to be
1131buggy in this release.
16537909
JH
1132
1133=back
1134
44a4342c
NIS
1135On all platforms the default set of layers should give acceptable results.
1136
ab4f7683 1137For UNIX platforms that will equivalent of "unix perlio" or "stdio".
44a4342c
NIS
1138Configure is setup to prefer "stdio" implementation if system's library
1139provides for fast access to the buffer, otherwise it uses the "unix perlio"
1140implementation.
1141
1142On Win32 the default in this release is "unix crlf". Win32's "stdio"
1143has a number of bugs/mis-features for perl IO which are somewhat
99366417 1144C compiler vendor/version dependent. Using our own C<crlf> layer as
44a4342c
NIS
1145the buffer avoids those issues and makes things more uniform.
1146The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1147buffering.
1148
1149This release uses C<unix> as the bottom layer on Win32 and so still uses C
1150compiler's numeric file descriptor routines. There is an experimental native
3d897973
IT
1151C<win32> layer which is expected to be enhanced and should eventually be
1152the default under Win32.
44a4342c
NIS
1153
1154=item PERLIO_DEBUG
d74e8afc 1155X<PERLIO_DEBUG>
44a4342c
NIS
1156
1157If set to the name of a file or device then certain operations of PerlIO
1158sub-system will be logged to that file (opened as append). Typical uses
1159are UNIX:
1160
1161 PERLIO_DEBUG=/dev/tty perl script ...
1162
1163and Win32 approximate equivalent:
1164
1165 set PERLIO_DEBUG=CON
1166 perl script ...
1167
923e8b21
RGS
1168This functionality is disabled for setuid scripts and for scripts run
1169with B<-T>.
16537909 1170
1e422769 1171=item PERLLIB
d74e8afc 1172X<PERLLIB>
1e422769 1173
48b971ca 1174A list of directories in which to look for Perl library
1e422769
PP
1175files before looking in the standard library and the current directory.
1176If PERL5LIB is defined, PERLLIB is not used.
1177
1178=item PERL5DB
d74e8afc 1179X<PERL5DB>
1e422769
PP
1180
1181The command used to load the debugger code. The default is:
1182
1183 BEGIN { require 'perl5db.pl' }
1184
2cbb2ee1 1185=item PERL5DB_THREADED
d74e8afc 1186X<PERL5DB_THREADED>
2cbb2ee1
RGS
1187
1188If set to a true value, indicates to the debugger that the code being
1189debugged uses threads.
1190
19799a22 1191=item PERL5SHELL (specific to the Win32 port)
d74e8afc 1192X<PERL5SHELL>
174c211a
GS
1193
1194May be set to an alternative shell that perl must use internally for
11998fdb 1195executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
ce1da67e 1196on WindowsNT and C<command.com /c> on Windows95. The value is considered
19799a22 1197to be space-separated. Precede any character that needs to be protected
ce1da67e
GS
1198(like a space or backslash) with a backslash.
1199
1200Note that Perl doesn't use COMSPEC for this purpose because
1201COMSPEC has a high degree of variability among users, leading to
1202portability concerns. Besides, perl can use a shell that may not be
1203fit for interactive use, and setting COMSPEC to such a shell may
1204interfere with the proper functioning of other programs (which usually
1205look in COMSPEC to find a shell fit for interactive use).
174c211a 1206
1c972609 1207=item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
d74e8afc 1208X<PERL_ALLOW_NON_IFS_LSP>
1c972609
SH
1209
1210Set to 1 to allow the use of non-IFS compatible LSP's.
1211Perl normally searches for an IFS-compatible LSP because this is required
1212for its emulation of Windows sockets as real filehandles. However, this may
1213cause problems if you have a firewall such as McAfee Guardian which requires
1214all applications to use its LSP which is not IFS-compatible, because clearly
1215Perl will normally avoid using such an LSP.
1216Setting this environment variable to 1 means that Perl will simply use the
1217first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1218happy (and in that particular case Perl still works too because McAfee
1219Guardian's LSP actually plays some other games which allow applications
1220requiring IFS compatibility to work).
1221
1e422769 1222=item PERL_DEBUG_MSTATS
d74e8afc 1223X<PERL_DEBUG_MSTATS>
1e422769 1224
67ce8856 1225Relevant only if perl is compiled with the malloc included with the perl
a3cb178b
GS
1226distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1227If set, this causes memory statistics to be dumped after execution. If set
1e422769
PP
1228to an integer greater than one, also causes memory statistics to be dumped
1229after compilation.
1230
1231=item PERL_DESTRUCT_LEVEL
d74e8afc 1232X<PERL_DESTRUCT_LEVEL>
1e422769
PP
1233
1234Relevant only if your perl executable was built with B<-DDEBUGGING>,
1235this controls the behavior of global destruction of objects and other
64cea5fd 1236references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
a0d0e21e 1237
02c7413a 1238=item PERL_DL_NONLAZY
d74e8afc 1239X<PERL_DL_NONLAZY>
02c7413a
GA
1240
1241Set to one to have perl resolve B<all> undefined symbols when it loads
1242a dynamic library. The default behaviour is to resolve symbols when
1243they are used. Setting this variable is useful during testing of
1244extensions as it ensures that you get an error on misspelled function
1245names even if the test suite doesn't call it.
1246
5d170f3a 1247=item PERL_ENCODING
d74e8afc 1248X<PERL_ENCODING>
5d170f3a
JH
1249
1250If using the C<encoding> pragma without an explicit encoding name, the
1251PERL_ENCODING environment variable is consulted for an encoding name.
1252
504f80c1 1253=item PERL_HASH_SEED
d74e8afc 1254X<PERL_HASH_SEED>
504f80c1 1255
183c3da1 1256(Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
4546b9e6
JH
1257To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1258exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1259things, that hash keys will be ordered the same between different runs
1260of Perl.
504f80c1 1261
4546b9e6
JH
1262The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1263If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1264behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
504f80c1
JH
1265
1266If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
1267the pseudorandom seed supplied by the operating system and libraries.
4546b9e6
JH
1268This means that each different run of Perl will have a different
1269ordering of the results of keys(), values(), and each().
504f80c1 1270
26a2d347
JH
1271B<Please note that the hash seed is sensitive information>. Hashes are
1272randomized to protect against local and remote attacks against Perl
1273code. By manually setting a seed this protection may be partially or
1274completely lost.
1275
1276See L<perlsec/"Algorithmic Complexity Attacks"> and
1277L</PERL_HASH_SEED_DEBUG> for more information.
504f80c1 1278
2191697e 1279=item PERL_HASH_SEED_DEBUG
d74e8afc 1280X<PERL_HASH_SEED_DEBUG>
2191697e 1281
e67b9e52 1282(Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
26a2d347
JH
1283the hash seed at the beginning of execution. This, combined with
1284L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1285behavior caused by hash randomization.
1286
1287B<Note that the hash seed is sensitive information>: by knowing it one
1288can craft a denial-of-service attack against Perl code, even remotely,
1289see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
e67b9e52 1290B<Do not disclose the hash seed> to people who don't need to know it.
9a7034eb 1291See also hash_seed() of L<Hash::Util>.
2191697e 1292
3d0ae7ba 1293=item PERL_ROOT (specific to the VMS port)
d74e8afc 1294X<PERL_ROOT>
3d0ae7ba
GS
1295
1296A translation concealed rooted logical name that contains perl and the
1297logical device for the @INC path on VMS only. Other logical names that
44a4342c
NIS
1298affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1299SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
3d0ae7ba
GS
1300L<perlvms> and in F<README.vms> in the Perl source distribution.
1301
4ffa73a3 1302=item PERL_SIGNALS
d74e8afc 1303X<PERL_SIGNALS>
4ffa73a3
JH
1304
1305In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1306signals behaviour (immediate but unsafe) is restored. If set to
ec488bcf 1307C<safe> the safe (or deferred) signals are used.
65c3f8ef 1308See L<perlipc/"Deferred Signals (Safe Signals)">.
4ffa73a3 1309
a05d7ebb 1310=item PERL_UNICODE
d74e8afc 1311X<PERL_UNICODE>
acae81db 1312
bf61ac64
JH
1313Equivalent to the B<-C> command-line switch. Note that this is not
1314a boolean variable-- setting this to C<"1"> is not the right way to
5b4f334e 1315"enable Unicode" (whatever that would mean). You can use C<"0"> to
e654d908
JH
1316"disable Unicode", though (or alternatively unset PERL_UNICODE in
1317your shell before starting Perl). See the description of the C<-C>
1318switch for more information.
acae81db 1319
3d0ae7ba 1320=item SYS$LOGIN (specific to the VMS port)
d74e8afc 1321X<SYS$LOGIN>
3d0ae7ba
GS
1322
1323Used if chdir has no argument and HOME and LOGDIR are not set.
1324
a0d0e21e 1325=back
1e422769
PP
1326
1327Perl also has environment variables that control how Perl handles data
1328specific to particular natural languages. See L<perllocale>.
1329
1330Apart from these, Perl uses no other environment variables, except
19799a22
GS
1331to make them available to the program being executed, and to child
1332processes. However, programs running setuid would do well to execute
1e422769
PP
1333the following lines before doing anything else, just to keep people
1334honest:
1335
19799a22 1336 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
7bac28a0 1337 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
c90c0ff4 1338 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};