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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> ]>
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8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[: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>] ]>
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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 S<[ B<-A [I<assertions>] >]>
18 S<[ B<-C [I<number/list>] >]>
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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
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112=head2 #! and quoting on non-Unix systems
113
114Unix's #! technique can be simulated on other systems:
115
116=over 4
117
118=item OS/2
119
120Put
121
122 extproc perl -S -your_switches
123
19799a22 124as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
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125`extproc' handling).
126
54310121 127=item MS-DOS
68dc0745 128
19799a22 129Create a batch file to run your program, and codify it in
fd1adc71 130C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
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131distribution for more information).
132
133=item Win95/NT
134
6c6a61e2 135The Win95/NT installation, when using the ActiveState installer for Perl,
c8db1d39 136will modify the Registry to associate the F<.pl> extension with the perl
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137interpreter. If you install Perl by other means (including building from
138the sources), you may have to modify the Registry yourself. Note that
139this means you can no longer tell the difference between an executable
140Perl program and a Perl library file.
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141
142=item Macintosh
143
19799a22 144A Macintosh perl program will have the appropriate Creator and
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145Type, so that double-clicking them will invoke the perl application.
146
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147=item VMS
148
149Put
150
151 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
152 $ exit++ + ++$status != 0 and $exit = $status = undef;
153
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154at the top of your program, where B<-mysw> are any command line switches you
155want to pass to Perl. You can now invoke the program directly, by saying
156C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
157via F<DCL$PATH> by just using the name of the program).
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158
159This incantation is a bit much to remember, but Perl will display it for
160you if you say C<perl "-V:startperl">.
161
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162=back
163
164Command-interpreters on non-Unix systems have rather different ideas
165on quoting than Unix shells. You'll need to learn the special
166characters in your command-interpreter (C<*>, C<\> and C<"> are
167common) and how to protect whitespace and these characters to run
19799a22 168one-liners (see B<-e> below).
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169
170On some systems, you may have to change single-quotes to double ones,
e6f03d26 171which you must I<not> do on Unix or Plan 9 systems. You might also
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172have to change a single % to a %%.
173
174For example:
175
176 # Unix
177 perl -e 'print "Hello world\n"'
178
54310121 179 # MS-DOS, etc.
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180 perl -e "print \"Hello world\n\""
181
54310121 182 # Macintosh
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183 print "Hello world\n"
184 (then Run "Myscript" or Shift-Command-R)
185
186 # VMS
187 perl -e "print ""Hello world\n"""
188
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189The problem is that none of this is reliable: it depends on the
190command and it is entirely possible neither works. If B<4DOS> were
191the command shell, this would probably work better:
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192
193 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
194
19799a22 195B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
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196when nobody was looking, but just try to find documentation for its
197quoting rules.
198
54310121 199Under the Macintosh, it depends which environment you are using. The MacPerl
68dc0745 200shell, or MPW, is much like Unix shells in its support for several
54310121 201quoting variants, except that it makes free use of the Macintosh's non-ASCII
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202characters as control characters.
203
204There is no general solution to all of this. It's just a mess.
205
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206=head2 Location of Perl
207
208It may seem obvious to say, but Perl is useful only when users can
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209easily find it. When possible, it's good for both F</usr/bin/perl>
210and F</usr/local/bin/perl> to be symlinks to the actual binary. If
211that can't be done, system administrators are strongly encouraged
212to put (symlinks to) perl and its accompanying utilities into a
213directory typically found along a user's PATH, or in some other
214obvious and convenient place.
215
216In this documentation, C<#!/usr/bin/perl> on the first line of the program
217will stand in for whatever method works on your system. You are
218advised to use a specific path if you care about a specific version.
a3cb178b 219
19799a22 220 #!/usr/local/bin/perl5.00554
a3cb178b 221
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222or if you just want to be running at least version, place a statement
223like this at the top of your program:
a0d0e21e 224
19799a22 225 use 5.005_54;
a0d0e21e 226
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227=head2 Command Switches
228
229As with all standard commands, a single-character switch may be
230clustered with the following switch, if any.
231
232 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
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233
234Switches include:
235
236=over 5
237
f2095865 238=item B<-0>[I<octal/hexadecimal>]
a0d0e21e 239
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240specifies the input record separator (C<$/>) as an octal or
241hexadecimal number. If there are no digits, the null character is the
242separator. Other switches may precede or follow the digits. For
243example, if you have a version of B<find> which can print filenames
244terminated by the null character, you can say this:
a0d0e21e 245
19799a22 246 find . -name '*.orig' -print0 | perl -n0e unlink
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247
248The special value 00 will cause Perl to slurp files in paragraph mode.
5f05dabc 249The value 0777 will cause Perl to slurp files whole because there is no
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250legal byte with that value.
251
252If you want to specify any Unicode character, use the hexadecimal
253format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
254(This means that you cannot use the C<-x> with a directory name that
255consists of hexadecimal digits.)
a0d0e21e 256
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257=item B<-A [I<assertions>]>
258
259Activates the assertions given after the switch as a comma-separated
260list of assertion names. If no assertion name is given, activates all
261assertions. See L<assertions>.
262
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263=item B<-a>
264
265turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
266split command to the @F array is done as the first thing inside the
267implicit while loop produced by the B<-n> or B<-p>.
268
269 perl -ane 'print pop(@F), "\n";'
270
271is equivalent to
272
273 while (<>) {
274 @F = split(' ');
275 print pop(@F), "\n";
276 }
277
278An alternate delimiter may be specified using B<-F>.
279
a05d7ebb 280=item B<-C [I<number/list>]>
46487f74 281
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282The C<-C> flag controls some Unicode of the Perl Unicode features.
283
284As of 5.8.1, the C<-C> can be followed either by a number or a list
f3f8427d 285of option letters. The letters, their numeric values, and effects
8aa8f774 286are as follows; listing the letters is equal to summing the numbers.
9f21530f 287
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288 I 1 STDIN is assumed to be in UTF-8
289 O 2 STDOUT will be in UTF-8
290 E 4 STDERR will be in UTF-8
291 S 7 I + O + E
292 i 8 UTF-8 is the default PerlIO layer for input streams
293 o 16 UTF-8 is the default PerlIO layer for output streams
294 D 24 i + o
295 A 32 the @ARGV elements are expected to be strings encoded
296 in UTF-8
297 L 64 normally the "IOEioA" are unconditional,
298 the L makes them conditional on the locale environment
299 variables (the LC_ALL, LC_TYPE, and LANG, in the order
300 of decreasing precedence) -- if the variables indicate
301 UTF-8, then the selected "IOEioA" are in effect
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302
303For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
304STDOUT and STDERR. Repeating letters is just redundant, not cumulative
305nor toggling.
a05d7ebb 306
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307The C<io> options mean that any subsequent open() (or similar I/O
308operations) will have the C<:utf8> PerlIO layer implicitly applied
309to them, in other words, UTF-8 is expected from any input stream,
310and UTF-8 is produced to any output stream. This is just the default,
311with explicit layers in open() and with binmode() one can manipulate
312streams as usual.
313
8aa8f774 314C<-C> on its own (not followed by any number or option list), or the
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315empty string C<""> for the C<PERL_UNICODE> environment variable, has the
316same effect as C<-CSDL>. In other words, the standard I/O handles and
317the default C<open()> layer are UTF-8-fied B<but> only if the locale
318environment variables indicate a UTF-8 locale. This behaviour follows
319the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
a05d7ebb 320
47427c4e 321You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
5b4f334e 322disable all the above Unicode features.
fde18df1 323
8aa8f774 324The read-only magic variable C<${^UNICODE}> reflects the numeric value
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325of this setting. This is variable is set during Perl startup and is
326thereafter read-only. If you want runtime effects, use the three-arg
2307c6d0 327open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
ab9e1bb7 328and the C<open> pragma (see L<open>).
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329
330(In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
331that enabled the use of Unicode-aware "wide system call" Win32 APIs.
332This feature was practically unused, however, and the command line
333switch was therefore "recycled".)
46487f74 334
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335=item B<-c>
336
19799a22 337causes Perl to check the syntax of the program and then exit without
7d30b5c4 338executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
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339C<use> blocks, because these are considered as occurring outside the
340execution of your program. C<INIT> and C<END> blocks, however, will
341be skipped.
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342
343=item B<-d>
344
19799a22 345runs the program under the Perl debugger. See L<perldebug>.
a0d0e21e 346
70c94a19 347=item B<-d:>I<foo[=bar,baz]>
3c81428c 348
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349runs the program under the control of a debugging, profiling, or
350tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
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351the program using the Devel::DProf profiler. As with the B<-M>
352flag, options may be passed to the Devel::foo package where they
353will be received and interpreted by the Devel::foo::import routine.
354The comma-separated list of options must follow a C<=> character.
355See L<perldebug>.
3c81428c 356
db2ba183 357=item B<-D>I<letters>
a0d0e21e 358
db2ba183 359=item B<-D>I<number>
a0d0e21e 360
19799a22 361sets debugging flags. To watch how it executes your program, use
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362B<-Dtls>. (This works only if debugging is compiled into your
363Perl.) Another nice value is B<-Dx>, which lists your compiled
4197b13f 364syntax tree. And B<-Dr> displays compiled regular expressions;
44a4342c 365the format of the output is explained in L<perldebguts>.
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366
367As an alternative, specify a number instead of list of letters (e.g.,
368B<-D14> is equivalent to B<-Dtls>):
a0d0e21e 369
9388183f 370 1 p Tokenizing and parsing (with v, displays parse stack)
db2ba183 371 2 s Stack snapshots
d6721266 372 with v, displays all stacks
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373 4 l Context (loop) stack processing
374 8 t Trace execution
375 16 o Method and overloading resolution
376 32 c String/numeric conversions
1045810a 377 64 P Print profiling info, preprocessor command for -P, source file input state
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378 128 m Memory allocation
379 256 f Format processing
380 512 r Regular expression parsing and execution
381 1024 x Syntax tree dump
382 2048 u Tainting checks
7bab3ede 383 4096 (Obsolete, previously used for LEAKTEST)
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384 8192 H Hash dump -- usurps values()
385 16384 X Scratchpad allocation
386 32768 D Cleaning up
8b73bbec 387 65536 S Thread synchronization
607df283 388 131072 T Tokenising
04932ac8 389 262144 R Include reference counts of dumped variables (eg when using -Ds)
1045810a 390 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
d6721266 391 1048576 v Verbose: use in conjunction with other flags
46187eeb 392 2097152 C Copy On Write
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393 4194304 A Consistency checks on internal structures
394 8388608 q quiet - currently only suppressed the "EXECUTING" message
a0d0e21e 395
19799a22 396All these flags require B<-DDEBUGGING> when you compile the Perl
1045810a 397executable (but see L<Devel::Peek>, L<re> which may change this).
44a4342c 398See the F<INSTALL> file in the Perl source distribution
19799a22 399for how to do this. This flag is automatically set if you include B<-g>
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400option when C<Configure> asks you about optimizer/debugger flags.
401
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402If you're just trying to get a print out of each line of Perl code
403as it executes, the way that C<sh -x> provides for shell scripts,
44a4342c 404you can't use Perl's B<-D> switch. Instead do this
19799a22 405
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406 # If you have "env" utility
407 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
408
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409 # Bourne shell syntax
410 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
411
412 # csh syntax
413 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
414
415See L<perldebug> for details and variations.
416
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417=item B<-e> I<commandline>
418
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419may be used to enter one line of program. If B<-e> is given, Perl
420will not look for a filename in the argument list. Multiple B<-e>
421commands may be given to build up a multi-line script. Make sure
422to use semicolons where you would in a normal program.
a0d0e21e 423
e0ebc809 424=item B<-F>I<pattern>
a0d0e21e 425
e0ebc809 426specifies the pattern to split on if B<-a> is also in effect. The
5f05dabc 427pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
e0ebc809 428put in single quotes.
a0d0e21e 429
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430=item B<-h>
431
432prints a summary of the options.
433
434=item B<-i>[I<extension>]
a0d0e21e 435
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436specifies that files processed by the C<E<lt>E<gt>> construct are to be
437edited in-place. It does this by renaming the input file, opening the
438output file by the original name, and selecting that output file as the
439default for print() statements. The extension, if supplied, is used to
440modify the name of the old file to make a backup copy, following these
441rules:
442
443If no extension is supplied, no backup is made and the current file is
444overwritten.
445
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446If the extension doesn't contain a C<*>, then it is appended to the
447end of the current filename as a suffix. If the extension does
448contain one or more C<*> characters, then each C<*> is replaced
449with the current filename. In Perl terms, you could think of this
450as:
2d259d92 451
66606d78 452 ($backup = $extension) =~ s/\*/$file_name/g;
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453
454This allows you to add a prefix to the backup file, instead of (or in
455addition to) a suffix:
456
ddffceb7 457 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
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458
459Or even to place backup copies of the original files into another
460directory (provided the directory already exists):
461
ddffceb7 462 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
2d259d92 463
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464These sets of one-liners are equivalent:
465
466 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
ddffceb7 467 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
66606d78 468
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469 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
470 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
66606d78 471
2d259d92 472From the shell, saying
a0d0e21e 473
19799a22 474 $ perl -p -i.orig -e "s/foo/bar/; ... "
a0d0e21e 475
19799a22 476is the same as using the program:
a0d0e21e 477
19799a22 478 #!/usr/bin/perl -pi.orig
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479 s/foo/bar/;
480
481which is equivalent to
482
483 #!/usr/bin/perl
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484 $extension = '.orig';
485 LINE: while (<>) {
a0d0e21e 486 if ($ARGV ne $oldargv) {
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487 if ($extension !~ /\*/) {
488 $backup = $ARGV . $extension;
489 }
490 else {
491 ($backup = $extension) =~ s/\*/$ARGV/g;
492 }
493 rename($ARGV, $backup);
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494 open(ARGVOUT, ">$ARGV");
495 select(ARGVOUT);
496 $oldargv = $ARGV;
497 }
498 s/foo/bar/;
499 }
500 continue {
501 print; # this prints to original filename
502 }
503 select(STDOUT);
504
505except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
506know when the filename has changed. It does, however, use ARGVOUT for
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507the selected filehandle. Note that STDOUT is restored as the default
508output filehandle after the loop.
509
510As shown above, Perl creates the backup file whether or not any output
511is actually changed. So this is just a fancy way to copy files:
512
cd2d1bac 513 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
19799a22 514or
cd2d1bac 515 $ perl -p -i'.orig' -e 1 file1 file2 file3...
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516
517You can use C<eof> without parentheses to locate the end of each input
518file, in case you want to append to each file, or reset line numbering
519(see example in L<perlfunc/eof>).
520
521If, for a given file, Perl is unable to create the backup file as
522specified in the extension then it will skip that file and continue on
523with the next one (if it exists).
524
19799a22 525For a discussion of issues surrounding file permissions and B<-i>,
cea6626f 526see 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
527
528You cannot use B<-i> to create directories or to strip extensions from
529files.
a0d0e21e 530
19799a22
GS
531Perl does not expand C<~> in filenames, which is good, since some
532folks use it for their backup files:
a0d0e21e 533
19799a22
GS
534 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
535
536Finally, the B<-i> switch does not impede execution when no
a2008d6d
GS
537files are given on the command line. In this case, no backup is made
538(the original file cannot, of course, be determined) and processing
539proceeds from STDIN to STDOUT as might be expected.
540
a0d0e21e
LW
541=item B<-I>I<directory>
542
e0ebc809 543Directories specified by B<-I> are prepended to the search path for
1fef88e7 544modules (C<@INC>), and also tells the C preprocessor where to search for
e0ebc809
PP
545include files. The C preprocessor is invoked with B<-P>; by default it
546searches /usr/include and /usr/lib/perl.
a0d0e21e 547
e0ebc809 548=item B<-l>[I<octnum>]
a0d0e21e 549
19799a22
GS
550enables automatic line-ending processing. It has two separate
551effects. First, it automatically chomps C<$/> (the input record
552separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
553(the output record separator) to have the value of I<octnum> so
554that any print statements will have that separator added back on.
555If I<octnum> is omitted, sets C<$\> to the current value of
556C<$/>. For instance, to trim lines to 80 columns:
a0d0e21e
LW
557
558 perl -lpe 'substr($_, 80) = ""'
559
560Note that the assignment C<$\ = $/> is done when the switch is processed,
561so the input record separator can be different than the output record
562separator if the B<-l> switch is followed by a B<-0> switch:
563
564 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
565
1fef88e7 566This sets C<$\> to newline and then sets C<$/> to the null character.
a0d0e21e 567
e0ebc809
PP
568=item B<-m>[B<->]I<module>
569
570=item B<-M>[B<->]I<module>
c07a80fd 571
e0ebc809
PP
572=item B<-M>[B<->]I<'module ...'>
573
574=item B<-[mM]>[B<->]I<module=arg[,arg]...>
3c81428c 575
19799a22
GS
576B<-m>I<module> executes C<use> I<module> C<();> before executing your
577program.
3c81428c 578
19799a22
GS
579B<-M>I<module> executes C<use> I<module> C<;> before executing your
580program. You can use quotes to add extra code after the module name,
581e.g., C<'-Mmodule qw(foo bar)'>.
3c81428c 582
19799a22 583If the first character after the B<-M> or B<-m> is a dash (C<->)
a5f75d66
AD
584then the 'use' is replaced with 'no'.
585
54310121 586A little builtin syntactic sugar means you can also say
19799a22
GS
587B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
588C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
589importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
e0ebc809 590C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
19799a22 591removes the distinction between B<-m> and B<-M>.
3c81428c 592
a0d0e21e
LW
593=item B<-n>
594
19799a22 595causes Perl to assume the following loop around your program, which
a0d0e21e
LW
596makes it iterate over filename arguments somewhat like B<sed -n> or
597B<awk>:
598
19799a22 599 LINE:
a0d0e21e 600 while (<>) {
19799a22 601 ... # your program goes here
a0d0e21e
LW
602 }
603
604Note that the lines are not printed by default. See B<-p> to have
08e9d68e 605lines printed. If a file named by an argument cannot be opened for
19799a22 606some reason, Perl warns you about it and moves on to the next file.
08e9d68e 607
9976c5c7
DM
608Here is an efficient way to delete all files that haven't been modifed for
609at least a week:
a0d0e21e 610
19799a22 611 find . -mtime +7 -print | perl -nle unlink
a0d0e21e 612
19799a22
GS
613This is faster than using the B<-exec> switch of B<find> because you don't
614have to start a process on every filename found. It does suffer from
615the bug of mishandling newlines in pathnames, which you can fix if
44a4342c 616you follow the example under B<-0>.
a0d0e21e
LW
617
618C<BEGIN> and C<END> blocks may be used to capture control before or after
19799a22 619the implicit program loop, just as in B<awk>.
a0d0e21e
LW
620
621=item B<-p>
622
19799a22 623causes Perl to assume the following loop around your program, which
a0d0e21e
LW
624makes it iterate over filename arguments somewhat like B<sed>:
625
626
19799a22 627 LINE:
a0d0e21e 628 while (<>) {
19799a22 629 ... # your program goes here
a0d0e21e 630 } continue {
08e9d68e 631 print or die "-p destination: $!\n";
a0d0e21e
LW
632 }
633
08e9d68e
DD
634If a file named by an argument cannot be opened for some reason, Perl
635warns you about it, and moves on to the next file. Note that the
c2611fb3 636lines are printed automatically. An error occurring during printing is
08e9d68e
DD
637treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
638overrides a B<-n> switch.
a0d0e21e
LW
639
640C<BEGIN> and C<END> blocks may be used to capture control before or after
19799a22 641the implicit loop, just as in B<awk>.
a0d0e21e
LW
642
643=item B<-P>
644
079a94c4
JH
645B<NOTE: Use of -P is strongly discouraged because of its inherent
646problems, including poor portability.>
647
648This option causes your program to be run through the C preprocessor before
efdf3af0 649compilation by Perl. Because both comments and B<cpp> directives begin
a0d0e21e 650with the # character, you should avoid starting comments with any words
efdf3af0 651recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
079a94c4
JH
652
653If you're considering using C<-P>, you might also want to look at the
654Filter::cpp module from CPAN.
655
656The problems of -P include, but are not limited to:
657
658=over 10
659
660=item *
661
662The C<#!> line is stripped, so any switches there don't apply.
663
664=item *
665
666A C<-P> on a C<#!> line doesn't work.
667
668=item *
669
670B<All> lines that begin with (whitespace and) a C<#> but
671do not look like cpp commands, are stripped, including anything
44a4342c 672inside Perl strings, regular expressions, and here-docs .
079a94c4
JH
673
674=item *
675
676In some platforms the C preprocessor knows too much: it knows about
677the C++ -style until-end-of-line comments starting with C<"//">.
efdf3af0
JH
678This will cause problems with common Perl constructs like
679
680 s/foo//;
681
682because after -P this will became illegal code
683
684 s/foo
685
686The workaround is to use some other quoting separator than C<"/">,
687like for example C<"!">:
688
689 s!foo!!;
a0d0e21e 690
079a94c4
JH
691
692
693=item *
694
695It requires not only a working C preprocessor but also a working
696F<sed>. If not on UNIX, you are probably out of luck on this.
697
698=item *
699
700Script line numbers are not preserved.
701
702=item *
703
704The C<-x> does not work with C<-P>.
705
706=back
9a1f07e7 707
a0d0e21e
LW
708=item B<-s>
709
19799a22
GS
710enables rudimentary switch parsing for switches on the command
711line after the program name but before any filename arguments (or before
3bbcc830
JP
712an argument of B<-->). This means you can have switches with two leading
713dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
19799a22 714corresponding variable in the Perl program. The following program
3c0facb2
GS
715prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
716if it is invoked with B<-xyz=abc>.
a0d0e21e
LW
717
718 #!/usr/bin/perl -s
3c0facb2 719 if ($xyz) { print "$xyz\n" }
a0d0e21e 720
3bbcc830
JP
721Do note that B<--help> creates the variable ${-help}, which is not compliant
722with C<strict refs>.
723
a0d0e21e
LW
724=item B<-S>
725
726makes Perl use the PATH environment variable to search for the
19799a22
GS
727program (unless the name of the program contains directory separators).
728
2a92aaa0
GS
729On some platforms, this also makes Perl append suffixes to the
730filename while searching for it. For example, on Win32 platforms,
731the ".bat" and ".cmd" suffixes are appended if a lookup for the
732original name fails, and if the name does not already end in one
733of those suffixes. If your Perl was compiled with DEBUGGING turned
734on, using the -Dp switch to Perl shows how the search progresses.
735
2a92aaa0
GS
736Typically this is used to emulate #! startup on platforms that
737don't support #!. This example works on many platforms that
738have a shell compatible with Bourne shell:
a0d0e21e
LW
739
740 #!/usr/bin/perl
a3cb178b 741 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
a0d0e21e
LW
742 if $running_under_some_shell;
743
19799a22
GS
744The system ignores the first line and feeds the program to F</bin/sh>,
745which proceeds to try to execute the Perl program as a shell script.
a0d0e21e
LW
746The shell executes the second line as a normal shell command, and thus
747starts up the Perl interpreter. On some systems $0 doesn't always
748contain the full pathname, so the B<-S> tells Perl to search for the
19799a22 749program if necessary. After Perl locates the program, it parses the
a0d0e21e 750lines and ignores them because the variable $running_under_some_shell
19799a22 751is never true. If the program will be interpreted by csh, you will need
a3cb178b
GS
752to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
753embedded spaces (and such) in the argument list. To start up sh rather
a0d0e21e
LW
754than csh, some systems may have to replace the #! line with a line
755containing just a colon, which will be politely ignored by Perl. Other
756systems can't control that, and need a totally devious construct that
19799a22 757will work under any of B<csh>, B<sh>, or Perl, such as the following:
a0d0e21e 758
19799a22 759 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
a3cb178b 760 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
5f05dabc 761 if $running_under_some_shell;
a0d0e21e 762
19799a22
GS
763If the filename supplied contains directory separators (i.e., is an
764absolute or relative pathname), and if that file is not found,
765platforms that append file extensions will do so and try to look
766for the file with those extensions added, one by one.
767
768On DOS-like platforms, if the program does not contain directory
769separators, it will first be searched for in the current directory
770before being searched for on the PATH. On Unix platforms, the
771program will be searched for strictly on the PATH.
772
6537fe72
MS
773=item B<-t>
774
775Like B<-T>, but taint checks will issue warnings rather than fatal
317ea90d
MS
776errors. These warnings can be controlled normally with C<no warnings
777qw(taint)>.
1dbad523
JH
778
779B<NOTE: this is not a substitute for -T.> This is meant only to be
780used as a temporary development aid while securing legacy code:
781for real production code and for new secure code written from scratch
782always use the real B<-T>.
6537fe72 783
a0d0e21e
LW
784=item B<-T>
785
a3cb178b 786forces "taint" checks to be turned on so you can test them. Ordinarily
19799a22
GS
787these checks are done only when running setuid or setgid. It's a
788good idea to turn them on explicitly for programs that run on behalf
789of someone else whom you might not necessarily trust, such as CGI
790programs or any internet servers you might write in Perl. See
791L<perlsec> for details. For security reasons, this option must be
792seen by Perl quite early; usually this means it must appear early
793on the command line or in the #! line for systems which support
794that construct.
a0d0e21e
LW
795
796=item B<-u>
797
19799a22
GS
798This obsolete switch causes Perl to dump core after compiling your
799program. You can then in theory take this core dump and turn it
800into an executable file by using the B<undump> program (not supplied).
801This speeds startup at the expense of some disk space (which you
802can minimize by stripping the executable). (Still, a "hello world"
803executable comes out to about 200K on my machine.) If you want to
804execute a portion of your program before dumping, use the dump()
805operator instead. Note: availability of B<undump> is platform
806specific and may not be available for a specific port of Perl.
807
808This switch has been superseded in favor of the new Perl code
809generator backends to the compiler. See L<B> and L<B::Bytecode>
810for details.
a0d0e21e
LW
811
812=item B<-U>
813
814allows Perl to do unsafe operations. Currently the only "unsafe"
815operations are the unlinking of directories while running as superuser,
816and running setuid programs with fatal taint checks turned into
19799a22
GS
817warnings. Note that the B<-w> switch (or the C<$^W> variable) must
818be used along with this option to actually I<generate> the
fb73857a 819taint-check warnings.
a0d0e21e
LW
820
821=item B<-v>
822
19799a22 823prints the version and patchlevel of your perl executable.
a0d0e21e 824
3c81428c
PP
825=item B<-V>
826
827prints summary of the major perl configuration values and the current
19799a22 828values of @INC.
3c81428c 829
e0ebc809 830=item B<-V:>I<name>
3c81428c
PP
831
832Prints to STDOUT the value of the named configuration variable.
44a4342c 833For example,
3c81428c 834
19799a22
GS
835 $ perl -V:man.dir
836
837will provide strong clues about what your MANPATH variable should
838be set to in order to access the Perl documentation.
a0d0e21e 839
19799a22 840=item B<-w>
774d564b 841
19799a22
GS
842prints warnings about dubious constructs, such as variable names
843that are mentioned only once and scalar variables that are used
844before being set, redefined subroutines, references to undefined
845filehandles or filehandles opened read-only that you are attempting
846to write on, values used as a number that doesn't look like numbers,
847using an array as though it were a scalar, if your subroutines
848recurse more than 100 deep, and innumerable other things.
849
b40da996 850This switch really just enables the internal C<$^W> variable. You
19799a22
GS
851can disable or promote into fatal errors specific warnings using
852C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
853See also L<perldiag> and L<perltrap>. A new, fine-grained warning
854facility is also available if you want to manipulate entire classes
9f1b1f2d 855of warnings; see L<warnings> or L<perllexwarn>.
a0d0e21e 856
0453d815
PM
857=item B<-W>
858
3c0facb2 859Enables all warnings regardless of C<no warnings> or C<$^W>.
0453d815
PM
860See L<perllexwarn>.
861
862=item B<-X>
863
3c0facb2 864Disables all warnings regardless of C<use warnings> or C<$^W>.
0453d815
PM
865See L<perllexwarn>.
866
a0d0e21e
LW
867=item B<-x> I<directory>
868
19799a22
GS
869tells Perl that the program is embedded in a larger chunk of unrelated
870ASCII text, such as in a mail message. Leading garbage will be
871discarded until the first line that starts with #! and contains the
872string "perl". Any meaningful switches on that line will be applied.
873If a directory name is specified, Perl will switch to that directory
874before running the program. The B<-x> switch controls only the
875disposal of leading garbage. The program must be terminated with
876C<__END__> if there is trailing garbage to be ignored (the program
877can process any or all of the trailing garbage via the DATA filehandle
878if desired).
a0d0e21e 879
1e422769
PP
880=back
881
882=head1 ENVIRONMENT
883
884=over 12
885
886=item HOME
887
888Used if chdir has no argument.
889
890=item LOGDIR
891
892Used if chdir has no argument and HOME is not set.
893
894=item PATH
895
19799a22 896Used in executing subprocesses, and in finding the program if B<-S> is
1e422769
PP
897used.
898
899=item PERL5LIB
900
48b971ca 901A list of directories in which to look for Perl library
1e422769 902files before looking in the standard library and the current
951ba7fe
GS
903directory. Any architecture-specific directories under the specified
904locations are automatically included if they exist. If PERL5LIB is not
48b971ca
RGS
905defined, PERLLIB is used. Directories are separated (like in PATH) by
906a colon on unixish platforms and by a semicolon on Windows (the proper
907path separator being given by the command C<perl -V:path_sep>).
951ba7fe
GS
908
909When running taint checks (either because the program was running setuid
910or setgid, or the B<-T> switch was used), neither variable is used.
911The program should instead say:
1e422769
PP
912
913 use lib "/my/directory";
914
54310121
PP
915=item PERL5OPT
916
917Command-line options (switches). Switches in this variable are taken
1c4db469 918as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
19799a22 919switches are allowed. When running taint checks (because the program
54310121 920was running setuid or setgid, or the B<-T> switch was used), this
74288ac8
GS
921variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
922enabled, and any subsequent options ignored.
54310121 923
16537909
JH
924=item PERLIO
925
44a4342c 926A space (or colon) separated list of PerlIO layers. If perl is built
03d9e98a 927to use PerlIO system for IO (the default) these layers effect perl's IO.
44a4342c
NIS
928
929It is conventional to start layer names with a colon e.g. C<:perlio> to
930emphasise their similarity to variable "attributes". But the code that parses
931layer specification strings (which is also used to decode the PERLIO
932environment variable) treats the colon as a separator.
933
3b0db4f9
JH
934An unset or empty PERLIO is equivalent to C<:stdio>.
935
44a4342c
NIS
936The list becomes the default for I<all> perl's IO. Consequently only built-in
937layers can appear in this list, as external layers (such as :encoding()) need
938IO in order to load them!. See L<"open pragma"|open> for how to add external
939encodings as defaults.
940
941The layers that it makes sense to include in the PERLIO environment
3d897973 942variable are briefly summarised below. For more details see L<PerlIO>.
16537909
JH
943
944=over 8
945
946=item :bytes
947
18aba96f
JH
948A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
949Unlikely to be useful on its own in the global PERLIO environment variable.
950You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
16537909
JH
951
952=item :crlf
953
3d897973
IT
954A layer which does CRLF to "\n" translation distinguishing "text" and
955"binary" files in the manner of MS-DOS and similar operating systems.
956(It currently does I<not> mimic MS-DOS as far as treating of Control-Z
957as being an end-of-file marker.)
44a4342c
NIS
958
959=item :mmap
960
961A layer which implements "reading" of files by using C<mmap()> to
962make (whole) file appear in the process's address space, and then
3d897973 963using that as PerlIO's "buffer".
16537909 964
44a4342c 965=item :perlio
16537909 966
3d897973
IT
967This is a re-implementation of "stdio-like" buffering written as a
968PerlIO "layer". As such it will call whatever layer is below it for
969its operations (typically C<:unix>).
16537909 970
18aba96f
JH
971=item :pop
972
973An experimental pseudolayer that removes the topmost layer.
3d897973 974Use with the same care as is reserved for nitroglycerin.
18aba96f 975
44a4342c 976=item :raw
16537909 977
18aba96f
JH
978A pseudolayer that manipulates other layers. Applying the <:raw>
979layer is equivalent to calling C<binmode($fh)>. It makes the stream
980pass each byte as-is without any translation. In particular CRLF
981translation, and/or :utf8 intuited from locale are disabled.
1cbfc93d 982
3d897973
IT
983Unlike in the earlier versions of Perl C<:raw> is I<not>
984just the inverse of C<:crlf> - other layers which would affect the
985binary nature of the stream are also removed or disabled.
16537909 986
44a4342c
NIS
987=item :stdio
988
989This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
990library calls. The layer provides both buffering and IO.
991Note that C<:stdio> layer does I<not> do CRLF translation even if that
992is platforms normal behaviour. You will need a C<:crlf> layer above it
993to do that.
994
995=item :unix
996
3d897973 997Low level layer which calls C<read>, C<write> and C<lseek> etc.
16537909
JH
998
999=item :utf8
1000
18aba96f 1001A pseudolayer that turns on a flag on the layer below to tell perl
3d897973
IT
1002that output should be in utf8 and that input should be regarded as
1003already in utf8 form. May be useful in PERLIO environment
1004variable to make UTF-8 the default. (To turn off that behaviour
1005use C<:bytes> layer.)
44a4342c
NIS
1006
1007=item :win32
1008
ab4f7683 1009On Win32 platforms this I<experimental> layer uses native "handle" IO
44a4342c
NIS
1010rather than unix-like numeric file descriptor layer. Known to be
1011buggy in this release.
16537909
JH
1012
1013=back
1014
44a4342c
NIS
1015On all platforms the default set of layers should give acceptable results.
1016
ab4f7683 1017For UNIX platforms that will equivalent of "unix perlio" or "stdio".
44a4342c
NIS
1018Configure is setup to prefer "stdio" implementation if system's library
1019provides for fast access to the buffer, otherwise it uses the "unix perlio"
1020implementation.
1021
1022On Win32 the default in this release is "unix crlf". Win32's "stdio"
1023has a number of bugs/mis-features for perl IO which are somewhat
99366417 1024C compiler vendor/version dependent. Using our own C<crlf> layer as
44a4342c
NIS
1025the buffer avoids those issues and makes things more uniform.
1026The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1027buffering.
1028
1029This release uses C<unix> as the bottom layer on Win32 and so still uses C
1030compiler's numeric file descriptor routines. There is an experimental native
3d897973
IT
1031C<win32> layer which is expected to be enhanced and should eventually be
1032the default under Win32.
44a4342c
NIS
1033
1034=item PERLIO_DEBUG
1035
1036If set to the name of a file or device then certain operations of PerlIO
1037sub-system will be logged to that file (opened as append). Typical uses
1038are UNIX:
1039
1040 PERLIO_DEBUG=/dev/tty perl script ...
1041
1042and Win32 approximate equivalent:
1043
1044 set PERLIO_DEBUG=CON
1045 perl script ...
1046
16537909 1047
1e422769
PP
1048=item PERLLIB
1049
48b971ca 1050A list of directories in which to look for Perl library
1e422769
PP
1051files before looking in the standard library and the current directory.
1052If PERL5LIB is defined, PERLLIB is not used.
1053
1054=item PERL5DB
1055
1056The command used to load the debugger code. The default is:
1057
1058 BEGIN { require 'perl5db.pl' }
1059
19799a22 1060=item PERL5SHELL (specific to the Win32 port)
174c211a
GS
1061
1062May be set to an alternative shell that perl must use internally for
11998fdb 1063executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
ce1da67e 1064on WindowsNT and C<command.com /c> on Windows95. The value is considered
19799a22 1065to be space-separated. Precede any character that needs to be protected
ce1da67e
GS
1066(like a space or backslash) with a backslash.
1067
1068Note that Perl doesn't use COMSPEC for this purpose because
1069COMSPEC has a high degree of variability among users, leading to
1070portability concerns. Besides, perl can use a shell that may not be
1071fit for interactive use, and setting COMSPEC to such a shell may
1072interfere with the proper functioning of other programs (which usually
1073look in COMSPEC to find a shell fit for interactive use).
174c211a 1074
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1075=item PERL_DEBUG_MSTATS
1076
67ce8856 1077Relevant only if perl is compiled with the malloc included with the perl
a3cb178b
GS
1078distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1079If set, this causes memory statistics to be dumped after execution. If set
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1080to an integer greater than one, also causes memory statistics to be dumped
1081after compilation.
1082
1083=item PERL_DESTRUCT_LEVEL
1084
1085Relevant only if your perl executable was built with B<-DDEBUGGING>,
1086this controls the behavior of global destruction of objects and other
64cea5fd 1087references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
a0d0e21e 1088
02c7413a
GA
1089=item PERL_DL_NONLAZY
1090
1091Set to one to have perl resolve B<all> undefined symbols when it loads
1092a dynamic library. The default behaviour is to resolve symbols when
1093they are used. Setting this variable is useful during testing of
1094extensions as it ensures that you get an error on misspelled function
1095names even if the test suite doesn't call it.
1096
5d170f3a
JH
1097=item PERL_ENCODING
1098
1099If using the C<encoding> pragma without an explicit encoding name, the
1100PERL_ENCODING environment variable is consulted for an encoding name.
1101
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JH
1102=item PERL_HASH_SEED
1103
183c3da1 1104(Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
4546b9e6
JH
1105To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1106exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1107things, that hash keys will be ordered the same between different runs
1108of Perl.
504f80c1 1109
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JH
1110The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1111If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1112behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
504f80c1
JH
1113
1114If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
1115the pseudorandom seed supplied by the operating system and libraries.
4546b9e6
JH
1116This means that each different run of Perl will have a different
1117ordering of the results of keys(), values(), and each().
504f80c1 1118
26a2d347
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1119B<Please note that the hash seed is sensitive information>. Hashes are
1120randomized to protect against local and remote attacks against Perl
1121code. By manually setting a seed this protection may be partially or
1122completely lost.
1123
1124See L<perlsec/"Algorithmic Complexity Attacks"> and
1125L</PERL_HASH_SEED_DEBUG> for more information.
504f80c1 1126
2191697e
JH
1127=item PERL_HASH_SEED_DEBUG
1128
e67b9e52 1129(Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
26a2d347
JH
1130the hash seed at the beginning of execution. This, combined with
1131L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1132behavior caused by hash randomization.
1133
1134B<Note that the hash seed is sensitive information>: by knowing it one
1135can craft a denial-of-service attack against Perl code, even remotely,
1136see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
e67b9e52 1137B<Do not disclose the hash seed> to people who don't need to know it.
9a7034eb 1138See also hash_seed() of L<Hash::Util>.
2191697e 1139
3d0ae7ba
GS
1140=item PERL_ROOT (specific to the VMS port)
1141
1142A translation concealed rooted logical name that contains perl and the
1143logical device for the @INC path on VMS only. Other logical names that
44a4342c
NIS
1144affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1145SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
3d0ae7ba
GS
1146L<perlvms> and in F<README.vms> in the Perl source distribution.
1147
4ffa73a3
JH
1148=item PERL_SIGNALS
1149
1150In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1151signals behaviour (immediate but unsafe) is restored. If set to
ec488bcf
JH
1152C<safe> the safe (or deferred) signals are used.
1153See L<perlipc/"Deferred Signals (Safe signals)">.
4ffa73a3 1154
a05d7ebb 1155=item PERL_UNICODE
acae81db 1156
bf61ac64
JH
1157Equivalent to the B<-C> command-line switch. Note that this is not
1158a boolean variable-- setting this to C<"1"> is not the right way to
5b4f334e 1159"enable Unicode" (whatever that would mean). You can use C<"0"> to
e654d908
JH
1160"disable Unicode", though (or alternatively unset PERL_UNICODE in
1161your shell before starting Perl). See the description of the C<-C>
1162switch for more information.
acae81db 1163
3d0ae7ba
GS
1164=item SYS$LOGIN (specific to the VMS port)
1165
1166Used if chdir has no argument and HOME and LOGDIR are not set.
1167
a0d0e21e 1168=back
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1169
1170Perl also has environment variables that control how Perl handles data
1171specific to particular natural languages. See L<perllocale>.
1172
1173Apart from these, Perl uses no other environment variables, except
19799a22
GS
1174to make them available to the program being executed, and to child
1175processes. However, programs running setuid would do well to execute
1e422769
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1176the following lines before doing anything else, just to keep people
1177honest:
1178
19799a22 1179 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
7bac28a0 1180 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
c90c0ff4 1181 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};