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