Commit | Line | Data |
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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlrun - how to execute the Perl interpreter | |
4 | ||
5 | =head1 SYNOPSIS | |
6 | ||
672fde27 | 7 | B<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> ]> |
c630fe62 | 12 | S<[ B<-C [I<number/list>] >]> |
e0ebc809 | 13 | S<[ B<-S> ]> |
14 | S<[ B<-x>[I<dir>] ]> | |
15 | S<[ B<-i>[I<extension>] ]> | |
eb1dd64e | 16 | S<[ [B<-e>|B<-E>] I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...> |
a0d0e21e LW |
17 | |
18 | =head1 DESCRIPTION | |
19 | ||
19799a22 GS |
20 | The normal way to run a Perl program is by making it directly |
21 | executable, or else by passing the name of the source file as an | |
22 | argument on the command line. (An interactive Perl environment | |
23 | is also possible--see L<perldebug> for details on how to do that.) | |
24 | Upon startup, Perl looks for your program in one of the following | |
a0d0e21e LW |
25 | places: |
26 | ||
27 | =over 4 | |
28 | ||
29 | =item 1. | |
30 | ||
bc9b29db | 31 | Specified line by line via B<-e> or B<-E> switches on the command line. |
a0d0e21e LW |
32 | |
33 | =item 2. | |
34 | ||
35 | Contained in the file specified by the first filename on the command line. | |
f4750dab | 36 | (Note that systems supporting the C<#!> notation invoke interpreters this |
a3cb178b | 37 | way. See L<Location of Perl>.) |
a0d0e21e LW |
38 | |
39 | =item 3. | |
40 | ||
5f05dabc | 41 | Passed in implicitly via standard input. This works only if there are |
19799a22 GS |
42 | no filename arguments--to pass arguments to a STDIN-read program you |
43 | must explicitly specify a "-" for the program name. | |
a0d0e21e LW |
44 | |
45 | =back | |
46 | ||
47 | With methods 2 and 3, Perl starts parsing the input file from the | |
48 | beginning, unless you've specified a B<-x> switch, in which case it | |
f4750dab | 49 | scans for the first line starting with C<#!> and containing the word |
19799a22 | 50 | "perl", and starts there instead. This is useful for running a program |
a0d0e21e | 51 | embedded in a larger message. (In this case you would indicate the end |
19799a22 | 52 | of the program using the C<__END__> token.) |
a0d0e21e | 53 | |
f4750dab | 54 | The C<#!> line is always examined for switches as the line is being |
5f05dabc | 55 | parsed. Thus, if you're on a machine that allows only one argument |
f4750dab TC |
56 | with the C<#!> line, or worse, doesn't even recognize the C<#!> line, you |
57 | still can get consistent switch behaviour regardless of how Perl was | |
19799a22 GS |
58 | invoked, even if B<-x> was used to find the beginning of the program. |
59 | ||
60 | Because historically some operating systems silently chopped off | |
f4750dab | 61 | kernel interpretation of the C<#!> line after 32 characters, some |
19799a22 GS |
62 | switches may be passed in on the command line, and some may not; |
63 | you could even get a "-" without its letter, if you're not careful. | |
64 | You probably want to make sure that all your switches fall either | |
65 | before or after that 32-character boundary. Most switches don't | |
66 | actually care if they're processed redundantly, but getting a "-" | |
67 | instead of a complete switch could cause Perl to try to execute | |
68 | standard input instead of your program. And a partial B<-I> switch | |
a0d0e21e LW |
69 | could also cause odd results. |
70 | ||
19799a22 GS |
71 | Some switches do care if they are processed twice, for instance |
72 | combinations of B<-l> and B<-0>. Either put all the switches after | |
73 | the 32-character boundary (if applicable), or replace the use of | |
74 | B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>. | |
fb73857a | 75 | |
f4750dab | 76 | Parsing of the C<#!> switches starts wherever "perl" is mentioned in the line. |
a0d0e21e LW |
77 | The sequences "-*" and "- " are specifically ignored so that you could, |
78 | if you were so inclined, say | |
79 | ||
428bacd7 SP |
80 | #!/bin/sh |
81 | #! -*-perl-*- | |
82 | eval 'exec perl -x -wS $0 ${1+"$@"}' | |
83 | if 0; | |
a0d0e21e | 84 | |
44a4342c | 85 | to let Perl see the B<-p> switch. |
19799a22 | 86 | |
f4750dab | 87 | A similar trick involves the I<env> program, if you have it. |
19799a22 GS |
88 | |
89 | #!/usr/bin/env perl | |
90 | ||
91 | The examples above use a relative path to the perl interpreter, | |
92 | getting whatever version is first in the user's path. If you want | |
6898e867 | 93 | a specific version of Perl, say, perl5.14.1, you should place |
f4750dab | 94 | that directly in the C<#!> line's path. |
a0d0e21e | 95 | |
2f1fe8a3 RGS |
96 | If the C<#!> line does not contain the word "perl" nor the word "indir" |
97 | the program named after the C<#!> is executed instead of the Perl | |
98 | interpreter. This is slightly bizarre, but it helps people on machines | |
99 | that don't do C<#!>, because they can tell a program that their SHELL is | |
100 | F</usr/bin/perl>, and Perl will then dispatch the program to the correct | |
101 | interpreter for them. | |
a0d0e21e | 102 | |
19799a22 | 103 | After locating your program, Perl compiles the entire program to an |
a0d0e21e | 104 | internal form. If there are any compilation errors, execution of the |
19799a22 | 105 | program is not attempted. (This is unlike the typical shell script, |
54310121 | 106 | which might run part-way through before finding a syntax error.) |
a0d0e21e | 107 | |
19799a22 | 108 | If the program is syntactically correct, it is executed. If the program |
a0d0e21e LW |
109 | runs off the end without hitting an exit() or die() operator, an implicit |
110 | C<exit(0)> is provided to indicate successful completion. | |
111 | ||
68dc0745 | 112 | =head2 #! and quoting on non-Unix systems |
d74e8afc | 113 | X<hashbang> X<#!> |
68dc0745 | 114 | |
f4750dab | 115 | Unix's C<#!> technique can be simulated on other systems: |
68dc0745 | 116 | |
117 | =over 4 | |
118 | ||
119 | =item OS/2 | |
120 | ||
121 | Put | |
122 | ||
123 | extproc perl -S -your_switches | |
124 | ||
19799a22 | 125 | as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's |
68dc0745 | 126 | `extproc' handling). |
127 | ||
54310121 | 128 | =item MS-DOS |
68dc0745 | 129 | |
19799a22 | 130 | Create a batch file to run your program, and codify it in |
fd1adc71 | 131 | C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source |
68dc0745 | 132 | distribution for more information). |
133 | ||
134 | =item Win95/NT | |
135 | ||
6c6a61e2 | 136 | The Win95/NT installation, when using the ActiveState installer for Perl, |
c8db1d39 | 137 | will modify the Registry to associate the F<.pl> extension with the perl |
6c6a61e2 GS |
138 | interpreter. If you install Perl by other means (including building from |
139 | the sources), you may have to modify the Registry yourself. Note that | |
140 | this means you can no longer tell the difference between an executable | |
141 | Perl program and a Perl library file. | |
68dc0745 | 142 | |
bd3fa61c CB |
143 | =item VMS |
144 | ||
145 | Put | |
146 | ||
60b7c710 KW |
147 | $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' ! |
148 | $ exit++ + ++$status != 0 and $exit = $status = undef; | |
bd3fa61c | 149 | |
19799a22 GS |
150 | at the top of your program, where B<-mysw> are any command line switches you |
151 | want to pass to Perl. You can now invoke the program directly, by saying | |
152 | C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly | |
153 | via F<DCL$PATH> by just using the name of the program). | |
bd3fa61c CB |
154 | |
155 | This incantation is a bit much to remember, but Perl will display it for | |
156 | you if you say C<perl "-V:startperl">. | |
157 | ||
68dc0745 | 158 | =back |
159 | ||
160 | Command-interpreters on non-Unix systems have rather different ideas | |
161 | on quoting than Unix shells. You'll need to learn the special | |
162 | characters in your command-interpreter (C<*>, C<\> and C<"> are | |
163 | common) and how to protect whitespace and these characters to run | |
76c9ab0e | 164 | one-liners (see L<-e|/-e commandline> below). |
68dc0745 | 165 | |
166 | On some systems, you may have to change single-quotes to double ones, | |
e6f03d26 | 167 | which you must I<not> do on Unix or Plan 9 systems. You might also |
68dc0745 | 168 | have to change a single % to a %%. |
169 | ||
170 | For example: | |
171 | ||
172 | # Unix | |
173 | perl -e 'print "Hello world\n"' | |
174 | ||
54310121 | 175 | # MS-DOS, etc. |
68dc0745 | 176 | perl -e "print \"Hello world\n\"" |
177 | ||
68dc0745 | 178 | # VMS |
179 | perl -e "print ""Hello world\n""" | |
180 | ||
19799a22 | 181 | The problem is that none of this is reliable: it depends on the |
f4750dab | 182 | command and it is entirely possible neither works. If I<4DOS> were |
19799a22 | 183 | the command shell, this would probably work better: |
68dc0745 | 184 | |
185 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
186 | ||
19799a22 | 187 | B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in |
68dc0745 | 188 | when nobody was looking, but just try to find documentation for its |
189 | quoting rules. | |
190 | ||
68dc0745 | 191 | There is no general solution to all of this. It's just a mess. |
192 | ||
a3cb178b | 193 | =head2 Location of Perl |
d74e8afc | 194 | X<perl, location of interpreter> |
a3cb178b GS |
195 | |
196 | It may seem obvious to say, but Perl is useful only when users can | |
19799a22 GS |
197 | easily find it. When possible, it's good for both F</usr/bin/perl> |
198 | and F</usr/local/bin/perl> to be symlinks to the actual binary. If | |
199 | that can't be done, system administrators are strongly encouraged | |
200 | to put (symlinks to) perl and its accompanying utilities into a | |
201 | directory typically found along a user's PATH, or in some other | |
202 | obvious and convenient place. | |
203 | ||
204 | In this documentation, C<#!/usr/bin/perl> on the first line of the program | |
205 | will stand in for whatever method works on your system. You are | |
206 | advised to use a specific path if you care about a specific version. | |
a3cb178b | 207 | |
6898e867 | 208 | #!/usr/local/bin/perl5.14 |
a3cb178b | 209 | |
19799a22 GS |
210 | or if you just want to be running at least version, place a statement |
211 | like this at the top of your program: | |
a0d0e21e | 212 | |
6898e867 | 213 | use 5.014; |
a0d0e21e | 214 | |
19799a22 | 215 | =head2 Command Switches |
d74e8afc | 216 | X<perl, command switches> X<command switches> |
19799a22 GS |
217 | |
218 | As with all standard commands, a single-character switch may be | |
219 | clustered with the following switch, if any. | |
220 | ||
221 | #!/usr/bin/perl -spi.orig # same as -s -p -i.orig | |
a0d0e21e | 222 | |
4612c2ba JK |
223 | A C<--> signals the end of options and disables further option processing. Any |
224 | arguments after the C<--> are treated as filenames and arguments. | |
225 | ||
a0d0e21e LW |
226 | Switches include: |
227 | ||
228 | =over 5 | |
229 | ||
f2095865 | 230 | =item B<-0>[I<octal/hexadecimal>] |
d74e8afc | 231 | X<-0> X<$/> |
a0d0e21e | 232 | |
f2095865 JH |
233 | specifies the input record separator (C<$/>) as an octal or |
234 | hexadecimal number. If there are no digits, the null character is the | |
235 | separator. Other switches may precede or follow the digits. For | |
f4750dab | 236 | example, if you have a version of I<find> which can print filenames |
f2095865 | 237 | terminated by the null character, you can say this: |
a0d0e21e | 238 | |
19799a22 | 239 | find . -name '*.orig' -print0 | perl -n0e unlink |
a0d0e21e LW |
240 | |
241 | The special value 00 will cause Perl to slurp files in paragraph mode. | |
7ba31cb4 KW |
242 | Any value 0400 or above will cause Perl to slurp files whole, but by convention |
243 | the value 0777 is the one normally used for this purpose. | |
f2095865 | 244 | |
7ba31cb4 | 245 | You can also specify the separator character using hexadecimal notation: |
f4750dab TC |
246 | B<-0xI<HHH...>>, where the C<I<H>> are valid hexadecimal digits. Unlike |
247 | the octal form, this one may be used to specify any Unicode character, even | |
248 | those beyond 0xFF. So if you I<really> want a record separator of 0777, | |
249 | specify it as B<-0x1FF>. (This means that you cannot use the B<-x> option | |
250 | with a directory name that consists of hexadecimal digits, or else Perl | |
251 | will think you have specified a hex number to B<-0>.) | |
a0d0e21e LW |
252 | |
253 | =item B<-a> | |
d74e8afc | 254 | X<-a> X<autosplit> |
a0d0e21e LW |
255 | |
256 | turns on autosplit mode when used with a B<-n> or B<-p>. An implicit | |
257 | split command to the @F array is done as the first thing inside the | |
258 | implicit while loop produced by the B<-n> or B<-p>. | |
259 | ||
260 | perl -ane 'print pop(@F), "\n";' | |
261 | ||
262 | is equivalent to | |
263 | ||
264 | while (<>) { | |
265 | @F = split(' '); | |
266 | print pop(@F), "\n"; | |
267 | } | |
268 | ||
269 | An alternate delimiter may be specified using B<-F>. | |
270 | ||
24ffa309 TC |
271 | B<-a> implicitly sets B<-n>. |
272 | ||
a05d7ebb | 273 | =item B<-C [I<number/list>]> |
d74e8afc | 274 | X<-C> |
46487f74 | 275 | |
f4750dab | 276 | The B<-C> flag controls some of the Perl Unicode features. |
a05d7ebb | 277 | |
f4750dab | 278 | As of 5.8.1, the B<-C> can be followed either by a number or a list |
f3f8427d | 279 | of option letters. The letters, their numeric values, and effects |
8aa8f774 | 280 | are as follows; listing the letters is equal to summing the numbers. |
9f21530f | 281 | |
73e12209 A |
282 | I 1 STDIN is assumed to be in UTF-8 |
283 | O 2 STDOUT will be in UTF-8 | |
284 | E 4 STDERR will be in UTF-8 | |
285 | S 7 I + O + E | |
286 | i 8 UTF-8 is the default PerlIO layer for input streams | |
287 | o 16 UTF-8 is the default PerlIO layer for output streams | |
288 | D 24 i + o | |
289 | A 32 the @ARGV elements are expected to be strings encoded | |
290 | in UTF-8 | |
60b7c710 KW |
291 | L 64 normally the "IOEioA" are unconditional, the L makes |
292 | them conditional on the locale environment variables | |
293 | (the LC_ALL, LC_TYPE, and LANG, in the order of | |
294 | decreasing precedence) -- if the variables indicate | |
73e12209 | 295 | UTF-8, then the selected "IOEioA" are in effect |
60b7c710 KW |
296 | a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching |
297 | code in debugging mode. | |
5a22a2bb NC |
298 | |
299 | =for documenting_the_underdocumented | |
300 | perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */" | |
9f21530f | 301 | |
f23930d5 NC |
302 | =for todo |
303 | perltodo mentions Unicode in %ENV and filenames. I guess that these will be | |
304 | options e and f (or F). | |
305 | ||
f4750dab | 306 | For example, B<-COE> and B<-C6> will both turn on UTF-8-ness on both |
9f21530f JH |
307 | STDOUT and STDERR. Repeating letters is just redundant, not cumulative |
308 | nor toggling. | |
a05d7ebb | 309 | |
44505768 | 310 | The C<io> options mean that any subsequent open() (or similar I/O |
88770b48 NT |
311 | operations) in the current file scope will have the C<:utf8> PerlIO layer |
312 | implicitly applied to them, in other words, UTF-8 is expected from any | |
313 | input stream, and UTF-8 is produced to any output stream. This is just | |
314 | the default, with explicit layers in open() and with binmode() one can | |
315 | manipulate streams as usual. | |
44505768 | 316 | |
f4750dab | 317 | B<-C> on its own (not followed by any number or option list), or the |
47427c4e | 318 | empty string C<""> for the C<PERL_UNICODE> environment variable, has the |
f4750dab TC |
319 | same effect as B<-CSDL>. In other words, the standard I/O handles and |
320 | the default C<open()> layer are UTF-8-fied I<but> only if the locale | |
47427c4e RGS |
321 | environment variables indicate a UTF-8 locale. This behaviour follows |
322 | the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0. | |
370155be | 323 | (See L<perl581delta/UTF-8 no longer default under UTF-8 locales>.) |
a05d7ebb | 324 | |
f4750dab | 325 | You can use B<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly |
5b4f334e | 326 | disable all the above Unicode features. |
fde18df1 | 327 | |
8aa8f774 | 328 | The read-only magic variable C<${^UNICODE}> reflects the numeric value |
f60ef620 | 329 | of this setting. This variable is set during Perl startup and is |
ab9e1bb7 | 330 | thereafter read-only. If you want runtime effects, use the three-arg |
2307c6d0 | 331 | open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>), |
ab9e1bb7 | 332 | and the C<open> pragma (see L<open>). |
fde18df1 | 333 | |
f4750dab | 334 | (In Perls earlier than 5.8.1 the B<-C> switch was a Win32-only switch |
fde18df1 JH |
335 | that enabled the use of Unicode-aware "wide system call" Win32 APIs. |
336 | This feature was practically unused, however, and the command line | |
337 | switch was therefore "recycled".) | |
46487f74 | 338 | |
f4750dab TC |
339 | B<Note:> Since perl 5.10.1, if the B<-C> option is used on the C<#!> line, |
340 | it must be specified on the command line as well, since the standard streams | |
618078e9 | 341 | are already set up at this point in the execution of the perl interpreter. |
4ba71d51 | 342 | You can also use binmode() to set the encoding of an I/O stream. |
618078e9 | 343 | |
a0d0e21e | 344 | =item B<-c> |
d74e8afc | 345 | X<-c> |
a0d0e21e | 346 | |
19799a22 | 347 | causes Perl to check the syntax of the program and then exit without |
f4750dab TC |
348 | executing it. Actually, it I<will> execute and C<BEGIN>, C<UNITCHECK>, |
349 | or C<CHECK> blocks and any C<use> statements: these are considered as | |
350 | occurring outside the execution of your program. C<INIT> and C<END> | |
351 | blocks, however, will be skipped. | |
a0d0e21e LW |
352 | |
353 | =item B<-d> | |
d74e8afc | 354 | X<-d> X<-dt> |
a0d0e21e | 355 | |
2cbb2ee1 RGS |
356 | =item B<-dt> |
357 | ||
19799a22 | 358 | runs the program under the Perl debugger. See L<perldebug>. |
2cbb2ee1 RGS |
359 | If B<t> is specified, it indicates to the debugger that threads |
360 | will be used in the code being debugged. | |
a0d0e21e | 361 | |
f4750dab | 362 | =item B<-d:>I<MOD[=bar,baz]> |
d74e8afc | 363 | X<-d> X<-dt> |
3c81428c | 364 | |
f4750dab | 365 | =item B<-dt:>I<MOD[=bar,baz]> |
2cbb2ee1 | 366 | |
f4750dab TC |
367 | runs the program under the control of a debugging, profiling, or tracing |
368 | module installed as C<Devel::I<MOD>>. E.g., B<-d:DProf> executes the | |
369 | program using the C<Devel::DProf> profiler. As with the B<-M> flag, options | |
370 | may be passed to the C<Devel::I<MOD>> package where they will be received | |
371 | and interpreted by the C<Devel::I<MOD>::import> routine. Again, like B<-M>, | |
372 | use -B<-d:-I<MOD>> to call C<Devel::I<MOD>::unimport> instead of import. The | |
373 | comma-separated list of options must follow a C<=> character. If B<t> is | |
374 | specified, it indicates to the debugger that threads will be used in the | |
375 | code being debugged. See L<perldebug>. | |
3c81428c | 376 | |
db2ba183 | 377 | =item B<-D>I<letters> |
d74e8afc | 378 | X<-D> X<DEBUGGING> X<-DDEBUGGING> |
a0d0e21e | 379 | |
db2ba183 | 380 | =item B<-D>I<number> |
a0d0e21e | 381 | |
19799a22 | 382 | sets debugging flags. To watch how it executes your program, use |
db2ba183 TB |
383 | B<-Dtls>. (This works only if debugging is compiled into your |
384 | Perl.) Another nice value is B<-Dx>, which lists your compiled | |
4197b13f | 385 | syntax tree. And B<-Dr> displays compiled regular expressions; |
44a4342c | 386 | the format of the output is explained in L<perldebguts>. |
4197b13f MJD |
387 | |
388 | As an alternative, specify a number instead of list of letters (e.g., | |
389 | B<-D14> is equivalent to B<-Dtls>): | |
a0d0e21e | 390 | |
9388183f | 391 | 1 p Tokenizing and parsing (with v, displays parse stack) |
3679267a | 392 | 2 s Stack snapshots (with v, displays all stacks) |
db2ba183 TB |
393 | 4 l Context (loop) stack processing |
394 | 8 t Trace execution | |
395 | 16 o Method and overloading resolution | |
396 | 32 c String/numeric conversions | |
4c84d7f2 | 397 | 64 P Print profiling info, source file input state |
d7a2c63c | 398 | 128 m Memory and SV allocation |
db2ba183 TB |
399 | 256 f Format processing |
400 | 512 r Regular expression parsing and execution | |
401 | 1024 x Syntax tree dump | |
402 | 2048 u Tainting checks | |
60b7c710 KW |
403 | 4096 U Unofficial, User hacking (reserved for private, |
404 | unreleased use) | |
db2ba183 TB |
405 | 8192 H Hash dump -- usurps values() |
406 | 16384 X Scratchpad allocation | |
407 | 32768 D Cleaning up | |
56967202 | 408 | 65536 S Op slab allocation |
f4750dab | 409 | 131072 T Tokenizing |
60b7c710 KW |
410 | 262144 R Include reference counts of dumped variables (eg when |
411 | using -Ds) | |
412 | 524288 J show s,t,P-debug (don't Jump over) on opcodes within | |
413 | package DB | |
d6721266 | 414 | 1048576 v Verbose: use in conjunction with other flags |
46187eeb | 415 | 2097152 C Copy On Write |
ecae49c0 | 416 | 4194304 A Consistency checks on internal structures |
60b7c710 KW |
417 | 8388608 q quiet - currently only suppresses the "EXECUTING" |
418 | message | |
d7c0d282 | 419 | 16777216 M trace smart match resolution |
60b7c710 KW |
420 | 33554432 B dump suBroutine definitions, including special Blocks |
421 | like BEGIN | |
a0d0e21e | 422 | |
19799a22 | 423 | All these flags require B<-DDEBUGGING> when you compile the Perl |
c85da6fc TH |
424 | executable (but see C<:opd> in L<Devel::Peek> or L<re/'debug' mode> |
425 | which may change this). | |
44a4342c | 426 | See the F<INSTALL> file in the Perl source distribution |
19799a22 | 427 | for how to do this. This flag is automatically set if you include B<-g> |
8c52afec IZ |
428 | option when C<Configure> asks you about optimizer/debugger flags. |
429 | ||
19799a22 GS |
430 | If you're just trying to get a print out of each line of Perl code |
431 | as it executes, the way that C<sh -x> provides for shell scripts, | |
44a4342c | 432 | you can't use Perl's B<-D> switch. Instead do this |
19799a22 | 433 | |
c406981e | 434 | # If you have "env" utility |
fdac53cd | 435 | env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program |
c406981e | 436 | |
19799a22 GS |
437 | # Bourne shell syntax |
438 | $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program | |
439 | ||
440 | # csh syntax | |
441 | % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program) | |
442 | ||
443 | See L<perldebug> for details and variations. | |
444 | ||
a0d0e21e | 445 | =item B<-e> I<commandline> |
d74e8afc | 446 | X<-e> |
a0d0e21e | 447 | |
19799a22 GS |
448 | may be used to enter one line of program. If B<-e> is given, Perl |
449 | will not look for a filename in the argument list. Multiple B<-e> | |
450 | commands may be given to build up a multi-line script. Make sure | |
451 | to use semicolons where you would in a normal program. | |
a0d0e21e | 452 | |
bc9b29db RH |
453 | =item B<-E> I<commandline> |
454 | X<-E> | |
455 | ||
456 | behaves just like B<-e>, except that it implicitly enables all | |
457 | optional features (in the main compilation unit). See L<feature>. | |
458 | ||
20ef40cf | 459 | =item B<-f> |
174299ac | 460 | X<-f> X<sitecustomize> X<sitecustomize.pl> |
20ef40cf | 461 | |
4a42f219 | 462 | Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup. |
20ef40cf GA |
463 | |
464 | Perl can be built so that it by default will try to execute | |
e846cbe5 | 465 | F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block). |
f4750dab TC |
466 | This is a hook that allows the sysadmin to customize how Perl behaves. |
467 | It can for instance be used to add entries to the @INC array to make Perl | |
e846cbe5 | 468 | find modules in non-standard locations. |
20ef40cf | 469 | |
298ca354 PBB |
470 | Perl actually inserts the following code: |
471 | ||
472 | BEGIN { | |
473 | do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; } | |
474 | && do "$Config{sitelib}/sitecustomize.pl"; | |
475 | } | |
476 | ||
477 | Since it is an actual C<do> (not a C<require>), F<sitecustomize.pl> | |
478 | doesn't need to return a true value. The code is run in package C<main>, | |
479 | in its own lexical scope. However, if the script dies, C<$@> will not | |
480 | be set. | |
481 | ||
482 | The value of C<$Config{sitelib}> is also determined in C code and not | |
483 | read from C<Config.pm>, which is not loaded. | |
484 | ||
f4750dab | 485 | The code is executed I<very> early. For example, any changes made to |
298ca354 PBB |
486 | C<@INC> will show up in the output of `perl -V`. Of course, C<END> |
487 | blocks will be likewise executed very late. | |
488 | ||
489 | To determine at runtime if this capability has been compiled in your | |
490 | perl, you can check the value of C<$Config{usesitecustomize}>. | |
491 | ||
e0ebc809 | 492 | =item B<-F>I<pattern> |
d74e8afc | 493 | X<-F> |
a0d0e21e | 494 | |
24ffa309 TC |
495 | specifies the pattern to split on for B<-a>. The pattern may be |
496 | surrounded by C<//>, C<"">, or C<''>, otherwise it will be put in single | |
497 | quotes. You can't use literal whitespace in the pattern. | |
498 | ||
499 | B<-F> implicitly sets both B<-a> and B<-n>. | |
a0d0e21e | 500 | |
e0ebc809 | 501 | =item B<-h> |
d74e8afc | 502 | X<-h> |
e0ebc809 | 503 | |
504 | prints a summary of the options. | |
505 | ||
506 | =item B<-i>[I<extension>] | |
d74e8afc | 507 | X<-i> X<in-place> |
a0d0e21e | 508 | |
2d259d92 CK |
509 | specifies that files processed by the C<E<lt>E<gt>> construct are to be |
510 | edited in-place. It does this by renaming the input file, opening the | |
511 | output file by the original name, and selecting that output file as the | |
512 | default for print() statements. The extension, if supplied, is used to | |
513 | modify the name of the old file to make a backup copy, following these | |
514 | rules: | |
515 | ||
479e5f87 PM |
516 | If no extension is supplied, and your system supports it, the original |
517 | I<file> is kept open without a name while the output is redirected to | |
518 | a new file with the original I<filename>. When perl exits, cleanly or not, | |
519 | the original I<file> is unlinked. | |
2d259d92 | 520 | |
19799a22 GS |
521 | If the extension doesn't contain a C<*>, then it is appended to the |
522 | end of the current filename as a suffix. If the extension does | |
523 | contain one or more C<*> characters, then each C<*> is replaced | |
524 | with the current filename. In Perl terms, you could think of this | |
525 | as: | |
2d259d92 | 526 | |
66606d78 | 527 | ($backup = $extension) =~ s/\*/$file_name/g; |
2d259d92 CK |
528 | |
529 | This allows you to add a prefix to the backup file, instead of (or in | |
530 | addition to) a suffix: | |
531 | ||
60b7c710 KW |
532 | $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to |
533 | # 'orig_fileA' | |
2d259d92 CK |
534 | |
535 | Or even to place backup copies of the original files into another | |
536 | directory (provided the directory already exists): | |
537 | ||
60b7c710 KW |
538 | $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to |
539 | # 'old/fileA.orig' | |
2d259d92 | 540 | |
66606d78 CK |
541 | These sets of one-liners are equivalent: |
542 | ||
60b7c710 KW |
543 | $ perl -pi -e 's/bar/baz/' fileA # overwrite current file |
544 | $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file | |
66606d78 | 545 | |
60b7c710 KW |
546 | $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' |
547 | $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' | |
66606d78 | 548 | |
2d259d92 | 549 | From the shell, saying |
a0d0e21e | 550 | |
19799a22 | 551 | $ perl -p -i.orig -e "s/foo/bar/; ... " |
a0d0e21e | 552 | |
19799a22 | 553 | is the same as using the program: |
a0d0e21e | 554 | |
19799a22 | 555 | #!/usr/bin/perl -pi.orig |
a0d0e21e LW |
556 | s/foo/bar/; |
557 | ||
558 | which is equivalent to | |
559 | ||
560 | #!/usr/bin/perl | |
19799a22 GS |
561 | $extension = '.orig'; |
562 | LINE: while (<>) { | |
a0d0e21e | 563 | if ($ARGV ne $oldargv) { |
66606d78 CK |
564 | if ($extension !~ /\*/) { |
565 | $backup = $ARGV . $extension; | |
566 | } | |
567 | else { | |
568 | ($backup = $extension) =~ s/\*/$ARGV/g; | |
569 | } | |
570 | rename($ARGV, $backup); | |
a0d0e21e LW |
571 | open(ARGVOUT, ">$ARGV"); |
572 | select(ARGVOUT); | |
573 | $oldargv = $ARGV; | |
574 | } | |
575 | s/foo/bar/; | |
576 | } | |
577 | continue { | |
578 | print; # this prints to original filename | |
579 | } | |
580 | select(STDOUT); | |
581 | ||
582 | except that the B<-i> form doesn't need to compare $ARGV to $oldargv to | |
583 | know when the filename has changed. It does, however, use ARGVOUT for | |
66606d78 CK |
584 | the selected filehandle. Note that STDOUT is restored as the default |
585 | output filehandle after the loop. | |
586 | ||
587 | As shown above, Perl creates the backup file whether or not any output | |
588 | is actually changed. So this is just a fancy way to copy files: | |
589 | ||
cd2d1bac | 590 | $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3... |
19799a22 | 591 | or |
cd2d1bac | 592 | $ perl -p -i'.orig' -e 1 file1 file2 file3... |
66606d78 CK |
593 | |
594 | You can use C<eof> without parentheses to locate the end of each input | |
595 | file, in case you want to append to each file, or reset line numbering | |
596 | (see example in L<perlfunc/eof>). | |
597 | ||
598 | If, for a given file, Perl is unable to create the backup file as | |
599 | specified in the extension then it will skip that file and continue on | |
600 | with the next one (if it exists). | |
601 | ||
1dcc3c19 DG |
602 | For a discussion of issues surrounding file permissions and B<-i>, see |
603 | L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber | |
604 | protected files? Isn't this a bug in Perl?>. | |
66606d78 CK |
605 | |
606 | You cannot use B<-i> to create directories or to strip extensions from | |
607 | files. | |
a0d0e21e | 608 | |
19799a22 GS |
609 | Perl does not expand C<~> in filenames, which is good, since some |
610 | folks use it for their backup files: | |
a0d0e21e | 611 | |
19799a22 GS |
612 | $ perl -pi~ -e 's/foo/bar/' file1 file2 file3... |
613 | ||
a66b22ca | 614 | Note that because B<-i> renames or deletes the original file before |
e1020413 | 615 | creating a new file of the same name, Unix-style soft and hard links will |
0cb0633f | 616 | not be preserved. |
a66b22ca | 617 | |
19799a22 | 618 | Finally, the B<-i> switch does not impede execution when no |
a2008d6d GS |
619 | files are given on the command line. In this case, no backup is made |
620 | (the original file cannot, of course, be determined) and processing | |
621 | proceeds from STDIN to STDOUT as might be expected. | |
622 | ||
a0d0e21e | 623 | =item B<-I>I<directory> |
d74e8afc | 624 | X<-I> X<@INC> |
a0d0e21e | 625 | |
e0ebc809 | 626 | Directories specified by B<-I> are prepended to the search path for |
4c84d7f2 | 627 | modules (C<@INC>). |
a0d0e21e | 628 | |
e0ebc809 | 629 | =item B<-l>[I<octnum>] |
d74e8afc | 630 | X<-l> X<$/> X<$\> |
a0d0e21e | 631 | |
19799a22 GS |
632 | enables automatic line-ending processing. It has two separate |
633 | effects. First, it automatically chomps C<$/> (the input record | |
634 | separator) when used with B<-n> or B<-p>. Second, it assigns C<$\> | |
635 | (the output record separator) to have the value of I<octnum> so | |
636 | that any print statements will have that separator added back on. | |
637 | If I<octnum> is omitted, sets C<$\> to the current value of | |
638 | C<$/>. For instance, to trim lines to 80 columns: | |
a0d0e21e LW |
639 | |
640 | perl -lpe 'substr($_, 80) = ""' | |
641 | ||
642 | Note that the assignment C<$\ = $/> is done when the switch is processed, | |
643 | so the input record separator can be different than the output record | |
644 | separator if the B<-l> switch is followed by a B<-0> switch: | |
645 | ||
646 | gnufind / -print0 | perl -ln0e 'print "found $_" if -p' | |
647 | ||
1fef88e7 | 648 | This sets C<$\> to newline and then sets C<$/> to the null character. |
a0d0e21e | 649 | |
e0ebc809 | 650 | =item B<-m>[B<->]I<module> |
d74e8afc | 651 | X<-m> X<-M> |
e0ebc809 | 652 | |
653 | =item B<-M>[B<->]I<module> | |
c07a80fd | 654 | |
e0ebc809 | 655 | =item B<-M>[B<->]I<'module ...'> |
656 | ||
657 | =item B<-[mM]>[B<->]I<module=arg[,arg]...> | |
3c81428c | 658 | |
19799a22 GS |
659 | B<-m>I<module> executes C<use> I<module> C<();> before executing your |
660 | program. | |
3c81428c | 661 | |
19799a22 GS |
662 | B<-M>I<module> executes C<use> I<module> C<;> before executing your |
663 | program. You can use quotes to add extra code after the module name, | |
f4750dab | 664 | e.g., C<'-MI<MODULE> qw(foo bar)'>. |
3c81428c | 665 | |
f4750dab | 666 | If the first character after the B<-M> or B<-m> is a dash (B<->) |
a5f75d66 AD |
667 | then the 'use' is replaced with 'no'. |
668 | ||
54310121 | 669 | A little builtin syntactic sugar means you can also say |
f4750dab TC |
670 | B<-mI<MODULE>=foo,bar> or B<-MI<MODULE>=foo,bar> as a shortcut for |
671 | B<'-MI<MODULE> qw(foo bar)'>. This avoids the need to use quotes when | |
672 | importing symbols. The actual code generated by B<-MI<MODULE>=foo,bar> is | |
e0ebc809 | 673 | C<use module split(/,/,q{foo,bar})>. Note that the C<=> form |
c2d9228f A |
674 | removes the distinction between B<-m> and B<-M>; that is, |
675 | B<-mI<MODULE>=foo,bar> is the same as B<-MI<MODULE>=foo,bar>. | |
3c81428c | 676 | |
f4750dab TC |
677 | A consequence of this is that B<-MI<MODULE>=number> never does a version check, |
678 | unless C<I<MODULE>::import()> itself is set up to do a version check, which | |
679 | could happen for example if I<MODULE> inherits from L<Exporter>. | |
642d0c2f | 680 | |
a0d0e21e | 681 | =item B<-n> |
d74e8afc | 682 | X<-n> |
a0d0e21e | 683 | |
19799a22 | 684 | causes Perl to assume the following loop around your program, which |
f4750dab TC |
685 | makes it iterate over filename arguments somewhat like I<sed -n> or |
686 | I<awk>: | |
a0d0e21e | 687 | |
19799a22 | 688 | LINE: |
a0d0e21e | 689 | while (<>) { |
19799a22 | 690 | ... # your program goes here |
a0d0e21e LW |
691 | } |
692 | ||
76c9ab0e | 693 | Note that the lines are not printed by default. See L</-p> to have |
08e9d68e | 694 | lines printed. If a file named by an argument cannot be opened for |
19799a22 | 695 | some reason, Perl warns you about it and moves on to the next file. |
08e9d68e | 696 | |
48ab5743 ML |
697 | Also note that C<< <> >> passes command line arguments to |
698 | L<perlfunc/open>, which doesn't necessarily interpret them as file names. | |
699 | See L<perlop> for possible security implications. | |
700 | ||
fa11829f | 701 | Here is an efficient way to delete all files that haven't been modified for |
9976c5c7 | 702 | at least a week: |
a0d0e21e | 703 | |
19799a22 | 704 | find . -mtime +7 -print | perl -nle unlink |
a0d0e21e | 705 | |
f4750dab | 706 | This is faster than using the B<-exec> switch of I<find> because you don't |
19799a22 GS |
707 | have to start a process on every filename found. It does suffer from |
708 | the bug of mishandling newlines in pathnames, which you can fix if | |
44a4342c | 709 | you follow the example under B<-0>. |
a0d0e21e LW |
710 | |
711 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
f4750dab | 712 | the implicit program loop, just as in I<awk>. |
a0d0e21e LW |
713 | |
714 | =item B<-p> | |
d74e8afc | 715 | X<-p> |
a0d0e21e | 716 | |
19799a22 | 717 | causes Perl to assume the following loop around your program, which |
f4750dab | 718 | makes it iterate over filename arguments somewhat like I<sed>: |
a0d0e21e LW |
719 | |
720 | ||
19799a22 | 721 | LINE: |
a0d0e21e | 722 | while (<>) { |
19799a22 | 723 | ... # your program goes here |
a0d0e21e | 724 | } continue { |
08e9d68e | 725 | print or die "-p destination: $!\n"; |
a0d0e21e LW |
726 | } |
727 | ||
08e9d68e DD |
728 | If a file named by an argument cannot be opened for some reason, Perl |
729 | warns you about it, and moves on to the next file. Note that the | |
c2611fb3 | 730 | lines are printed automatically. An error occurring during printing is |
08e9d68e DD |
731 | treated as fatal. To suppress printing use the B<-n> switch. A B<-p> |
732 | overrides a B<-n> switch. | |
a0d0e21e LW |
733 | |
734 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
f4750dab | 735 | the implicit loop, just as in I<awk>. |
a0d0e21e | 736 | |
a0d0e21e | 737 | =item B<-s> |
d74e8afc | 738 | X<-s> |
a0d0e21e | 739 | |
19799a22 GS |
740 | enables rudimentary switch parsing for switches on the command |
741 | line after the program name but before any filename arguments (or before | |
74ac850a | 742 | an argument of B<-->). Any switch found there is removed from @ARGV and sets the |
19799a22 | 743 | corresponding variable in the Perl program. The following program |
3c0facb2 GS |
744 | prints "1" if the program is invoked with a B<-xyz> switch, and "abc" |
745 | if it is invoked with B<-xyz=abc>. | |
a0d0e21e LW |
746 | |
747 | #!/usr/bin/perl -s | |
3c0facb2 | 748 | if ($xyz) { print "$xyz\n" } |
a0d0e21e | 749 | |
1dcc3c19 DG |
750 | Do note that a switch like B<--help> creates the variable C<${-help}>, which is |
751 | not compliant with C<use strict "refs">. Also, when using this option on a | |
752 | script with warnings enabled you may get a lot of spurious "used only once" | |
753 | warnings. | |
3bbcc830 | 754 | |
a0d0e21e | 755 | =item B<-S> |
d74e8afc | 756 | X<-S> |
a0d0e21e LW |
757 | |
758 | makes Perl use the PATH environment variable to search for the | |
f4750dab | 759 | program unless the name of the program contains path separators. |
19799a22 | 760 | |
2a92aaa0 GS |
761 | On some platforms, this also makes Perl append suffixes to the |
762 | filename while searching for it. For example, on Win32 platforms, | |
763 | the ".bat" and ".cmd" suffixes are appended if a lookup for the | |
764 | original name fails, and if the name does not already end in one | |
f4750dab TC |
765 | of those suffixes. If your Perl was compiled with C<DEBUGGING> turned |
766 | on, using the B<-Dp> switch to Perl shows how the search progresses. | |
2a92aaa0 | 767 | |
f4750dab TC |
768 | Typically this is used to emulate C<#!> startup on platforms that don't |
769 | support C<#!>. It's also convenient when debugging a script that uses C<#!>, | |
fa3aa65a JC |
770 | and is thus normally found by the shell's $PATH search mechanism. |
771 | ||
772 | This example works on many platforms that have a shell compatible with | |
773 | Bourne shell: | |
a0d0e21e LW |
774 | |
775 | #!/usr/bin/perl | |
a3cb178b | 776 | eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}' |
a0d0e21e LW |
777 | if $running_under_some_shell; |
778 | ||
19799a22 GS |
779 | The system ignores the first line and feeds the program to F</bin/sh>, |
780 | which proceeds to try to execute the Perl program as a shell script. | |
a0d0e21e LW |
781 | The shell executes the second line as a normal shell command, and thus |
782 | starts up the Perl interpreter. On some systems $0 doesn't always | |
783 | contain the full pathname, so the B<-S> tells Perl to search for the | |
19799a22 | 784 | program if necessary. After Perl locates the program, it parses the |
a0d0e21e | 785 | lines and ignores them because the variable $running_under_some_shell |
19799a22 | 786 | is never true. If the program will be interpreted by csh, you will need |
a3cb178b | 787 | to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand |
f4750dab TC |
788 | embedded spaces (and such) in the argument list. To start up I<sh> rather |
789 | than I<csh>, some systems may have to replace the C<#!> line with a line | |
a0d0e21e LW |
790 | containing just a colon, which will be politely ignored by Perl. Other |
791 | systems can't control that, and need a totally devious construct that | |
f4750dab | 792 | will work under any of I<csh>, I<sh>, or Perl, such as the following: |
a0d0e21e | 793 | |
19799a22 | 794 | eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}' |
a3cb178b | 795 | & eval 'exec /usr/bin/perl -wS $0 $argv:q' |
5f05dabc | 796 | if $running_under_some_shell; |
a0d0e21e | 797 | |
f4750dab | 798 | If the filename supplied contains directory separators (and so is an |
19799a22 GS |
799 | absolute or relative pathname), and if that file is not found, |
800 | platforms that append file extensions will do so and try to look | |
801 | for the file with those extensions added, one by one. | |
802 | ||
803 | On DOS-like platforms, if the program does not contain directory | |
804 | separators, it will first be searched for in the current directory | |
805 | before being searched for on the PATH. On Unix platforms, the | |
806 | program will be searched for strictly on the PATH. | |
807 | ||
6537fe72 | 808 | =item B<-t> |
d74e8afc | 809 | X<-t> |
6537fe72 MS |
810 | |
811 | Like B<-T>, but taint checks will issue warnings rather than fatal | |
f4750dab | 812 | errors. These warnings can now be controlled normally with C<no warnings |
317ea90d | 813 | qw(taint)>. |
1dbad523 | 814 | |
f4750dab TC |
815 | B<Note: This is not a substitute for C<-T>!> This is meant to be |
816 | used I<only> as a temporary development aid while securing legacy code: | |
817 | for real production code and for new secure code written from scratch, | |
1dbad523 | 818 | always use the real B<-T>. |
6537fe72 | 819 | |
a0d0e21e | 820 | =item B<-T> |
d74e8afc | 821 | X<-T> |
a0d0e21e | 822 | |
f4750dab | 823 | turns on "taint" so you can test them. Ordinarily |
19799a22 GS |
824 | these checks are done only when running setuid or setgid. It's a |
825 | good idea to turn them on explicitly for programs that run on behalf | |
826 | of someone else whom you might not necessarily trust, such as CGI | |
827 | programs or any internet servers you might write in Perl. See | |
828 | L<perlsec> for details. For security reasons, this option must be | |
829 | seen by Perl quite early; usually this means it must appear early | |
f4750dab | 830 | on the command line or in the C<#!> line for systems which support |
19799a22 | 831 | that construct. |
a0d0e21e LW |
832 | |
833 | =item B<-u> | |
d74e8afc | 834 | X<-u> |
a0d0e21e | 835 | |
f4750dab | 836 | This switch causes Perl to dump core after compiling your |
19799a22 | 837 | program. You can then in theory take this core dump and turn it |
f4750dab | 838 | into an executable file by using the I<undump> program (not supplied). |
19799a22 GS |
839 | This speeds startup at the expense of some disk space (which you |
840 | can minimize by stripping the executable). (Still, a "hello world" | |
841 | executable comes out to about 200K on my machine.) If you want to | |
842 | execute a portion of your program before dumping, use the dump() | |
f4750dab | 843 | operator instead. Note: availability of I<undump> is platform |
19799a22 GS |
844 | specific and may not be available for a specific port of Perl. |
845 | ||
a0d0e21e | 846 | =item B<-U> |
d74e8afc | 847 | X<-U> |
a0d0e21e LW |
848 | |
849 | allows Perl to do unsafe operations. Currently the only "unsafe" | |
f4750dab TC |
850 | operations are attempting to unlink directories while running as superuser |
851 | and running setuid programs with fatal taint checks turned into warnings. | |
852 | Note that warnings must be enabled along with this option to actually | |
853 | I<generate> the taint-check warnings. | |
a0d0e21e LW |
854 | |
855 | =item B<-v> | |
d74e8afc | 856 | X<-v> |
a0d0e21e | 857 | |
19799a22 | 858 | prints the version and patchlevel of your perl executable. |
a0d0e21e | 859 | |
3c81428c | 860 | =item B<-V> |
d74e8afc | 861 | X<-V> |
3c81428c | 862 | |
863 | prints summary of the major perl configuration values and the current | |
19799a22 | 864 | values of @INC. |
3c81428c | 865 | |
307dc113 | 866 | =item B<-V:>I<configvar> |
3c81428c | 867 | |
4a305f6a | 868 | Prints to STDOUT the value of the named configuration variable(s), |
f4750dab | 869 | with multiples when your C<I<configvar>> argument looks like a regex (has |
307dc113 | 870 | non-letters). For example: |
3c81428c | 871 | |
307dc113 JC |
872 | $ perl -V:libc |
873 | libc='/lib/libc-2.2.4.so'; | |
4a305f6a JC |
874 | $ perl -V:lib. |
875 | libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc'; | |
876 | libc='/lib/libc-2.2.4.so'; | |
877 | $ perl -V:lib.* | |
878 | libpth='/usr/local/lib /lib /usr/lib'; | |
879 | libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc'; | |
880 | lib_ext='.a'; | |
881 | libc='/lib/libc-2.2.4.so'; | |
882 | libperl='libperl.a'; | |
883 | .... | |
884 | ||
885 | Additionally, extra colons can be used to control formatting. A | |
f4750dab | 886 | trailing colon suppresses the linefeed and terminator ";", allowing |
4a305f6a | 887 | you to embed queries into shell commands. (mnemonic: PATH separator |
f4750dab | 888 | ":".) |
4a305f6a JC |
889 | |
890 | $ echo "compression-vars: " `perl -V:z.*: ` " are here !" | |
891 | compression-vars: zcat='' zip='zip' are here ! | |
892 | ||
f4750dab | 893 | A leading colon removes the "name=" part of the response, this allows |
307dc113 | 894 | you to map to the name you need. (mnemonic: empty label) |
4a305f6a JC |
895 | |
896 | $ echo "goodvfork="`./perl -Ilib -V::usevfork` | |
897 | goodvfork=false; | |
898 | ||
899 | Leading and trailing colons can be used together if you need | |
900 | positional parameter values without the names. Note that in the case | |
f4750dab | 901 | below, the C<PERL_API> params are returned in alphabetical order. |
4a305f6a JC |
902 | |
903 | $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now | |
904 | building_on 'linux' '5' '1' '9' now | |
a0d0e21e | 905 | |
19799a22 | 906 | =item B<-w> |
d74e8afc | 907 | X<-w> |
774d564b | 908 | |
19799a22 | 909 | prints warnings about dubious constructs, such as variable names |
f4750dab TC |
910 | mentioned only once and scalar variables used |
911 | before being set; redefined subroutines; references to undefined | |
912 | filehandles; filehandles opened read-only that you are attempting | |
913 | to write on; values used as a number that don't I<look> like numbers; | |
914 | using an array as though it were a scalar; if your subroutines | |
915 | recurse more than 100 deep; and innumerable other things. | |
916 | ||
917 | This switch really just enables the global C<$^W> variable; normally, | |
918 | the lexically scoped C<use warnings> pragma is preferred. You | |
19799a22 GS |
919 | can disable or promote into fatal errors specific warnings using |
920 | C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>. | |
f4750dab | 921 | See also L<perldiag> and L<perltrap>. A fine-grained warning |
19799a22 | 922 | facility is also available if you want to manipulate entire classes |
44ecbbd8 | 923 | of warnings; see L<warnings>. |
a0d0e21e | 924 | |
0453d815 | 925 | =item B<-W> |
d74e8afc | 926 | X<-W> |
0453d815 | 927 | |
3c0facb2 | 928 | Enables all warnings regardless of C<no warnings> or C<$^W>. |
44ecbbd8 | 929 | See L<warnings>. |
0453d815 PM |
930 | |
931 | =item B<-X> | |
d74e8afc | 932 | X<-X> |
0453d815 | 933 | |
3c0facb2 | 934 | Disables all warnings regardless of C<use warnings> or C<$^W>. |
44ecbbd8 | 935 | See L<warnings>. |
0453d815 | 936 | |
136e4fd6 | 937 | =item B<-x> |
d74e8afc | 938 | X<-x> |
136e4fd6 | 939 | |
d3bf4b0e | 940 | =item B<-x>I<directory> |
a0d0e21e | 941 | |
19799a22 | 942 | tells Perl that the program is embedded in a larger chunk of unrelated |
f4750dab TC |
943 | text, such as in a mail message. Leading garbage will be |
944 | discarded until the first line that starts with C<#!> and contains the | |
19799a22 | 945 | string "perl". Any meaningful switches on that line will be applied. |
3d6c2ba7 B |
946 | |
947 | All references to line numbers by the program (warnings, errors, ...) | |
f4750dab TC |
948 | will treat the C<#!> line as the first line. |
949 | Thus a warning on the 2nd line of the program, which is on the 100th | |
950 | line in the file will be reported as line 2, not as line 100. | |
951 | This can be overridden by using the C<#line> directive. | |
96090e4f | 952 | (See L<perlsyn/"Plain Old Comments (Not!)">) |
3d6c2ba7 | 953 | |
19799a22 GS |
954 | If a directory name is specified, Perl will switch to that directory |
955 | before running the program. The B<-x> switch controls only the | |
956 | disposal of leading garbage. The program must be terminated with | |
f4750dab TC |
957 | C<__END__> if there is trailing garbage to be ignored; the program |
958 | can process any or all of the trailing garbage via the C<DATA> filehandle | |
959 | if desired. | |
a0d0e21e | 960 | |
353c6505 | 961 | The directory, if specified, must appear immediately following the B<-x> |
d3bf4b0e DN |
962 | with no intervening whitespace. |
963 | ||
1e422769 | 964 | =back |
965 | ||
966 | =head1 ENVIRONMENT | |
d74e8afc | 967 | X<perl, environment variables> |
1e422769 | 968 | |
969 | =over 12 | |
970 | ||
971 | =item HOME | |
d74e8afc | 972 | X<HOME> |
1e422769 | 973 | |
f4750dab | 974 | Used if C<chdir> has no argument. |
1e422769 | 975 | |
976 | =item LOGDIR | |
d74e8afc | 977 | X<LOGDIR> |
1e422769 | 978 | |
f4750dab | 979 | Used if C<chdir> has no argument and HOME is not set. |
1e422769 | 980 | |
981 | =item PATH | |
d74e8afc | 982 | X<PATH> |
1e422769 | 983 | |
19799a22 | 984 | Used in executing subprocesses, and in finding the program if B<-S> is |
1e422769 | 985 | used. |
986 | ||
987 | =item PERL5LIB | |
d74e8afc | 988 | X<PERL5LIB> |
1e422769 | 989 | |
48b971ca | 990 | A list of directories in which to look for Perl library |
1e422769 | 991 | files before looking in the standard library and the current |
4b85e17e AD |
992 | directory. Any architecture-specific and version-specific directories, |
993 | such as F<version/archname/>, F<version/>, or F<archname/> under the | |
994 | specified locations are automatically included if they exist, with this | |
995 | lookup done at interpreter startup time. In addition, any directories | |
996 | matching the entries in C<$Config{inc_version_list}> are added. | |
997 | (These typically would be for older compatible perl versions installed | |
998 | in the same directory tree.) | |
69681433 A |
999 | |
1000 | If PERL5LIB is not defined, PERLLIB is used. Directories are separated | |
e1020413 | 1001 | (like in PATH) by a colon on Unixish platforms and by a semicolon on |
69681433 | 1002 | Windows (the proper path separator being given by the command C<perl |
f4750dab | 1003 | -V:I<path_sep>>). |
951ba7fe | 1004 | |
f4750dab TC |
1005 | When running taint checks, either because the program was running setuid or |
1006 | setgid, or the B<-T> or B<-t> switch was specified, neither PERL5LIB nor | |
1007 | PERLLIB is consulted. The program should instead say: | |
1e422769 | 1008 | |
1009 | use lib "/my/directory"; | |
1010 | ||
54310121 | 1011 | =item PERL5OPT |
d74e8afc | 1012 | X<PERL5OPT> |
54310121 | 1013 | |
f4750dab | 1014 | Command-line options (switches). Switches in this variable are treated |
2b622f1a | 1015 | as if they were on every Perl command line. Only the B<-[CDIMUdmtwW]> |
f4750dab TC |
1016 | switches are allowed. When running taint checks (either because the |
1017 | program was running setuid or setgid, or because the B<-T> or B<-t> | |
1018 | switch was used), this variable is ignored. If PERL5OPT begins with | |
cce9fd8c | 1019 | B<-T>, tainting will be enabled and subsequent options ignored. If |
f4750dab TC |
1020 | PERL5OPT begins with B<-t>, tainting will be enabled, a writable dot |
1021 | removed from @INC, and subsequent options honored. | |
54310121 | 1022 | |
16537909 | 1023 | =item PERLIO |
d74e8afc | 1024 | X<PERLIO> |
16537909 | 1025 | |
44a4342c | 1026 | A space (or colon) separated list of PerlIO layers. If perl is built |
f4750dab | 1027 | to use PerlIO system for IO (the default) these layers affect Perl's IO. |
44a4342c | 1028 | |
f4750dab TC |
1029 | It is conventional to start layer names with a colon (for example, C<:perlio>) to |
1030 | emphasize their similarity to variable "attributes". But the code that parses | |
cce9fd8c | 1031 | layer specification strings, which is also used to decode the PERLIO |
f4750dab | 1032 | environment variable, treats the colon as a separator. |
44a4342c | 1033 | |
5b64f2bf | 1034 | An unset or empty PERLIO is equivalent to the default set of layers for |
f4750dab | 1035 | your platform; for example, C<:unix:perlio> on Unix-like systems |
1f070127 | 1036 | and C<:unix:crlf> on Windows and other DOS-like systems. |
3b0db4f9 | 1037 | |
f4750dab TC |
1038 | The list becomes the default for I<all> Perl's IO. Consequently only built-in |
1039 | layers can appear in this list, as external layers (such as C<:encoding()>) need | |
cce9fd8c | 1040 | IO in order to load them! See L<"open pragma"|open> for how to add external |
44a4342c NIS |
1041 | encodings as defaults. |
1042 | ||
f4750dab TC |
1043 | Layers it makes sense to include in the PERLIO environment |
1044 | variable are briefly summarized below. For more details see L<PerlIO>. | |
16537909 JH |
1045 | |
1046 | =over 8 | |
1047 | ||
1048 | =item :bytes | |
d74e8afc | 1049 | X<:bytes> |
16537909 | 1050 | |
f4750dab TC |
1051 | A pseudolayer that turns the C<:utf8> flag I<off> for the layer below; |
1052 | unlikely to be useful on its own in the global PERLIO environment variable. | |
18aba96f | 1053 | You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>. |
16537909 JH |
1054 | |
1055 | =item :crlf | |
d74e8afc | 1056 | X<:crlf> |
16537909 | 1057 | |
f4750dab | 1058 | A layer which does CRLF to C<"\n"> translation distinguishing "text" and |
3d897973 IT |
1059 | "binary" files in the manner of MS-DOS and similar operating systems. |
1060 | (It currently does I<not> mimic MS-DOS as far as treating of Control-Z | |
1061 | as being an end-of-file marker.) | |
44a4342c NIS |
1062 | |
1063 | =item :mmap | |
d74e8afc | 1064 | X<:mmap> |
44a4342c | 1065 | |
f4750dab TC |
1066 | A layer that implements "reading" of files by using I<mmap>(2) to |
1067 | make an entire file appear in the process's address space, and then | |
3d897973 | 1068 | using that as PerlIO's "buffer". |
16537909 | 1069 | |
44a4342c | 1070 | =item :perlio |
d74e8afc | 1071 | X<:perlio> |
16537909 | 1072 | |
f4750dab TC |
1073 | This is a re-implementation of stdio-like buffering written as a |
1074 | PerlIO layer. As such it will call whatever layer is below it for | |
1075 | its operations, typically C<:unix>. | |
16537909 | 1076 | |
18aba96f | 1077 | =item :pop |
d74e8afc | 1078 | X<:pop> |
18aba96f JH |
1079 | |
1080 | An experimental pseudolayer that removes the topmost layer. | |
f4750dab | 1081 | Use with the same care as is reserved for nitroglycerine. |
18aba96f | 1082 | |
44a4342c | 1083 | =item :raw |
d74e8afc | 1084 | X<:raw> |
16537909 | 1085 | |
136e4fd6 | 1086 | A pseudolayer that manipulates other layers. Applying the C<:raw> |
18aba96f | 1087 | layer is equivalent to calling C<binmode($fh)>. It makes the stream |
f4750dab TC |
1088 | pass each byte as-is without translation. In particular, both CRLF |
1089 | translation and intuiting C<:utf8> from the locale are disabled. | |
1cbfc93d | 1090 | |
f4750dab TC |
1091 | Unlike in earlier versions of Perl, C<:raw> is I<not> |
1092 | just the inverse of C<:crlf>: other layers which would affect the | |
3d897973 | 1093 | binary nature of the stream are also removed or disabled. |
16537909 | 1094 | |
44a4342c | 1095 | =item :stdio |
d74e8afc | 1096 | X<:stdio> |
44a4342c | 1097 | |
f4750dab | 1098 | This layer provides a PerlIO interface by wrapping system's ANSI C "stdio" |
44a4342c | 1099 | library calls. The layer provides both buffering and IO. |
f4750dab TC |
1100 | Note that the C<:stdio> layer does I<not> do CRLF translation even if that |
1101 | is the platform's normal behaviour. You will need a C<:crlf> layer above it | |
44a4342c NIS |
1102 | to do that. |
1103 | ||
1104 | =item :unix | |
d74e8afc | 1105 | X<:unix> |
44a4342c | 1106 | |
f4750dab | 1107 | Low-level layer that calls C<read>, C<write>, C<lseek>, etc. |
16537909 JH |
1108 | |
1109 | =item :utf8 | |
d74e8afc | 1110 | X<:utf8> |
16537909 | 1111 | |
f4750dab | 1112 | A pseudolayer that enables a flag in the layer below to tell Perl |
3d897973 | 1113 | that output should be in utf8 and that input should be regarded as |
f4750dab TC |
1114 | already in valid utf8 form. B<WARNING: It does not check for validity and as such |
1115 | should be handled with extreme caution for input, because security violations | |
1116 | can occur with non-shortest UTF-8 encodings, etc.> Generally C<:encoding(utf8)> is | |
740d4bb2 | 1117 | the best option when reading UTF-8 encoded data. |
44a4342c NIS |
1118 | |
1119 | =item :win32 | |
d74e8afc | 1120 | X<:win32> |
44a4342c | 1121 | |
ab4f7683 | 1122 | On Win32 platforms this I<experimental> layer uses native "handle" IO |
f4750dab TC |
1123 | rather than a Unix-like numeric file descriptor layer. Known to be |
1124 | buggy in this release (5.14). | |
16537909 JH |
1125 | |
1126 | =back | |
1127 | ||
f4750dab | 1128 | The default set of layers should give acceptable results on all platforms |
44a4342c | 1129 | |
f4750dab TC |
1130 | For Unix platforms that will be the equivalent of "unix perlio" or "stdio". |
1131 | Configure is set up to prefer the "stdio" implementation if the system's library | |
1132 | provides for fast access to the buffer; otherwise, it uses the "unix perlio" | |
44a4342c NIS |
1133 | implementation. |
1134 | ||
f4750dab TC |
1135 | On Win32 the default in this release (5.14) is "unix crlf". Win32's "stdio" |
1136 | has a number of bugs/mis-features for Perl IO which are somewhat depending | |
1137 | on the version and vendor of the C compiler. Using our own C<crlf> layer as | |
1138 | the buffer avoids those issues and makes things more uniform. The C<crlf> | |
1139 | layer provides CRLF conversion as well as buffering. | |
44a4342c | 1140 | |
f4750dab TC |
1141 | This release (5.14) uses C<unix> as the bottom layer on Win32, and so still |
1142 | uses the C compiler's numeric file descriptor routines. There is an | |
1143 | experimental native C<win32> layer, which is expected to be enhanced and | |
1144 | should eventually become the default under Win32. | |
44a4342c | 1145 | |
f4750dab | 1146 | The PERLIO environment variable is completely ignored when Perl |
5437faeb PF |
1147 | is run in taint mode. |
1148 | ||
44a4342c | 1149 | =item PERLIO_DEBUG |
d74e8afc | 1150 | X<PERLIO_DEBUG> |
44a4342c | 1151 | |
f4750dab | 1152 | If set to the name of a file or device, certain operations of PerlIO |
cce9fd8c | 1153 | subsystem will be logged to that file, which is opened in append mode. |
f4750dab | 1154 | Typical uses are in Unix: |
44a4342c | 1155 | |
f4750dab | 1156 | % env PERLIO_DEBUG=/dev/tty perl script ... |
44a4342c | 1157 | |
f4750dab | 1158 | and under Win32, the approximately equivalent: |
44a4342c | 1159 | |
f4750dab | 1160 | > set PERLIO_DEBUG=CON |
44a4342c NIS |
1161 | perl script ... |
1162 | ||
923e8b21 RGS |
1163 | This functionality is disabled for setuid scripts and for scripts run |
1164 | with B<-T>. | |
16537909 | 1165 | |
1e422769 | 1166 | =item PERLLIB |
d74e8afc | 1167 | X<PERLLIB> |
1e422769 | 1168 | |
48b971ca | 1169 | A list of directories in which to look for Perl library |
1e422769 | 1170 | files before looking in the standard library and the current directory. |
1171 | If PERL5LIB is defined, PERLLIB is not used. | |
1172 | ||
f4750dab | 1173 | The PERLLIB environment variable is completely ignored when Perl |
5437faeb PF |
1174 | is run in taint mode. |
1175 | ||
1e422769 | 1176 | =item PERL5DB |
d74e8afc | 1177 | X<PERL5DB> |
1e422769 | 1178 | |
1179 | The command used to load the debugger code. The default is: | |
1180 | ||
f4750dab | 1181 | BEGIN { require "perl5db.pl" } |
1e422769 | 1182 | |
f4750dab | 1183 | The PERL5DB environment variable is only used when Perl is started with |
5437faeb PF |
1184 | a bare B<-d> switch. |
1185 | ||
2cbb2ee1 | 1186 | =item PERL5DB_THREADED |
d74e8afc | 1187 | X<PERL5DB_THREADED> |
2cbb2ee1 RGS |
1188 | |
1189 | If set to a true value, indicates to the debugger that the code being | |
1190 | debugged uses threads. | |
1191 | ||
19799a22 | 1192 | =item PERL5SHELL (specific to the Win32 port) |
d74e8afc | 1193 | X<PERL5SHELL> |
174c211a | 1194 | |
f4750dab TC |
1195 | On Win32 ports only, may be set to an alternative shell that Perl must use |
1196 | internally for executing "backtick" commands or system(). Default is | |
1197 | C<cmd.exe /x/d/c> on WindowsNT and C<command.com /c> on Windows95. The | |
1198 | value is considered space-separated. Precede any character that | |
1199 | needs to be protected, like a space or backslash, with another backslash. | |
ce1da67e GS |
1200 | |
1201 | Note that Perl doesn't use COMSPEC for this purpose because | |
1202 | COMSPEC has a high degree of variability among users, leading to | |
f4750dab | 1203 | portability concerns. Besides, Perl can use a shell that may not be |
ce1da67e GS |
1204 | fit for interactive use, and setting COMSPEC to such a shell may |
1205 | interfere with the proper functioning of other programs (which usually | |
1206 | look in COMSPEC to find a shell fit for interactive use). | |
174c211a | 1207 | |
5437faeb PF |
1208 | Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked |
1209 | when running external commands. It is recommended that | |
1210 | you explicitly set (or delete) C<$ENV{PERL5SHELL}> when running | |
1211 | in taint mode under Windows. | |
1212 | ||
1c972609 | 1213 | =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port) |
d74e8afc | 1214 | X<PERL_ALLOW_NON_IFS_LSP> |
1c972609 | 1215 | |
f4750dab | 1216 | Set to 1 to allow the use of non-IFS compatible LSPs (Layered Service Providers). |
1c972609 SH |
1217 | Perl normally searches for an IFS-compatible LSP because this is required |
1218 | for its emulation of Windows sockets as real filehandles. However, this may | |
f4750dab TC |
1219 | cause problems if you have a firewall such as I<McAfee Guardian>, which requires |
1220 | that all applications use its LSP but which is not IFS-compatible, because clearly | |
1c972609 | 1221 | Perl will normally avoid using such an LSP. |
f4750dab | 1222 | |
1c972609 | 1223 | Setting this environment variable to 1 means that Perl will simply use the |
f4750dab TC |
1224 | first suitable LSP enumerated in the catalog, which keeps I<McAfee Guardian> |
1225 | happy--and in that particular case Perl still works too because I<McAfee | |
1226 | Guardian>'s LSP actually plays other games which allow applications | |
1227 | requiring IFS compatibility to work. | |
1c972609 | 1228 | |
1e422769 | 1229 | =item PERL_DEBUG_MSTATS |
d74e8afc | 1230 | X<PERL_DEBUG_MSTATS> |
1e422769 | 1231 | |
f4750dab TC |
1232 | Relevant only if Perl is compiled with the C<malloc> included with the Perl |
1233 | distribution; that is, if C<perl -V:d_mymalloc> is "define". | |
1234 | ||
1235 | If set, this dumps out memory statistics after execution. If set | |
1236 | to an integer greater than one, also dumps out memory statistics | |
1e422769 | 1237 | after compilation. |
1238 | ||
1239 | =item PERL_DESTRUCT_LEVEL | |
d74e8afc | 1240 | X<PERL_DESTRUCT_LEVEL> |
1e422769 | 1241 | |
f4750dab TC |
1242 | Relevant only if your Perl executable was built with B<-DDEBUGGING>, |
1243 | this controls the behaviour of global destruction of objects and other | |
96090e4f | 1244 | references. See L<perlhacktips/PERL_DESTRUCT_LEVEL> for more information. |
a0d0e21e | 1245 | |
02c7413a | 1246 | =item PERL_DL_NONLAZY |
d74e8afc | 1247 | X<PERL_DL_NONLAZY> |
02c7413a | 1248 | |
f4750dab | 1249 | Set to C<"1"> to have Perl resolve I<all> undefined symbols when it loads |
02c7413a GA |
1250 | a dynamic library. The default behaviour is to resolve symbols when |
1251 | they are used. Setting this variable is useful during testing of | |
f4750dab TC |
1252 | extensions, as it ensures that you get an error on misspelled function |
1253 | names even if the test suite doesn't call them. | |
02c7413a | 1254 | |
5d170f3a | 1255 | =item PERL_ENCODING |
d74e8afc | 1256 | X<PERL_ENCODING> |
5d170f3a | 1257 | |
f4750dab | 1258 | If using the C<use encoding> pragma without an explicit encoding name, the |
5d170f3a JH |
1259 | PERL_ENCODING environment variable is consulted for an encoding name. |
1260 | ||
504f80c1 | 1261 | =item PERL_HASH_SEED |
d74e8afc | 1262 | X<PERL_HASH_SEED> |
504f80c1 | 1263 | |
6a5b4183 YO |
1264 | (Since Perl 5.8.1, new semantics in Perl 5.18.0) Used to override |
1265 | the randomization of Perl's internal hash function. The value is expressed | |
1266 | in hexadecimal, and may include a leading 0x. Truncated patterns | |
1267 | are treated as though they are suffixed with sufficient 0's as required. | |
8d4a1e6c | 1268 | |
6a5b4183 YO |
1269 | If the option is provided, and C<PERL_PERTURB_KEYS> is NOT set, then |
1270 | a value of '0' implies C<PERL_PERTURB_KEYS=0> and any other value | |
1271 | implies C<PERL_PERTURB_KEYS=2>. | |
504f80c1 | 1272 | |
f4750dab | 1273 | B<PLEASE NOTE: The hash seed is sensitive information>. Hashes are |
26a2d347 | 1274 | randomized to protect against local and remote attacks against Perl |
f4750dab | 1275 | code. By manually setting a seed, this protection may be partially or |
26a2d347 JH |
1276 | completely lost. |
1277 | ||
4a70680a | 1278 | See L<perlsec/"Algorithmic Complexity Attacks">, L</PERL_PERTURB_KEYS>, and |
26a2d347 | 1279 | L</PERL_HASH_SEED_DEBUG> for more information. |
504f80c1 | 1280 | |
6a5b4183 YO |
1281 | =item PERL_PERTURB_KEYS |
1282 | X<PERL_PERTURB_KEYS> | |
1283 | ||
1284 | (Since Perl 5.18.0) Set to C<"0"> or C<"NO"> then traversing keys | |
e6b54db6 | 1285 | will be repeatable from run to run for the same PERL_HASH_SEED. |
6a5b4183 YO |
1286 | Insertion into a hash will not change the order, except to provide |
1287 | for more space in the hash. When combined with setting PERL_HASH_SEED | |
1288 | this mode is as close to pre 5.18 behavior as you can get. | |
1289 | ||
1290 | When set to C<"1"> or C<"RANDOM"> then traversing keys will be randomized. | |
1291 | Every time a hash is inserted into the key order will change in a random | |
e6b54db6 | 1292 | fashion. The order may not be repeatable in a following program run |
6a5b4183 YO |
1293 | even if the PERL_HASH_SEED has been specified. This is the default |
1294 | mode for perl. | |
1295 | ||
1296 | When set to C<"2"> or C<"DETERMINISTIC"> then inserting keys into a hash | |
e6b54db6 | 1297 | will cause the key order to change, but in a way that is repeatable |
6a5b4183 YO |
1298 | from program run to program run. |
1299 | ||
1300 | B<NOTE:> Use of this option is considered insecure, and is intended only | |
1301 | for debugging non-deterministic behavior in Perl's hash function. Do | |
1302 | not use it in production. | |
1303 | ||
1304 | See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_HASH_SEED> | |
1305 | and L</PERL_HASH_SEED_DEBUG> for more information. You can get and set the | |
1306 | key traversal mask for a specific hash by using the C<hash_traversal_mask()> | |
1307 | function from L<Hash::Util>. | |
1308 | ||
2191697e | 1309 | =item PERL_HASH_SEED_DEBUG |
d74e8afc | 1310 | X<PERL_HASH_SEED_DEBUG> |
2191697e | 1311 | |
6a5b4183 YO |
1312 | (Since Perl 5.8.1.) Set to C<"1"> to display (to STDERR) information |
1313 | about the hash function, seed, and what type of key traversal | |
1314 | randomization is in effect at the beginning of execution. This, combined | |
1315 | with L</PERL_HASH_SEED> and L</PERL_PERTURB_KEYS> is intended to aid in | |
1316 | debugging nondeterministic behaviour caused by hash randomization. | |
1317 | ||
1318 | B<Note> that any information about the hash function, especially the hash | |
1319 | seed is B<sensitive information>: by knowing it, one can craft a denial-of-service | |
1320 | attack against Perl code, even remotely; see L<perlsec/"Algorithmic Complexity Attacks"> | |
1321 | for more information. B<Do not disclose the hash seed> to people who | |
1322 | don't need to know it. See also C<hash_seed()> and | |
1323 | C<key_traversal_mask()> in L<Hash::Util>. | |
1324 | ||
1325 | An example output might be: | |
26a2d347 | 1326 | |
6a5b4183 | 1327 | HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM) |
2191697e | 1328 | |
9aa9f499 JC |
1329 | =item PERL_MEM_LOG |
1330 | X<PERL_MEM_LOG> | |
1331 | ||
f4750dab | 1332 | If your Perl was configured with B<-Accflags=-DPERL_MEM_LOG>, setting |
7916a455 | 1333 | the environment variable C<PERL_MEM_LOG> enables logging debug |
f4750dab TC |
1334 | messages. The value has the form C<< <I<number>>[m][s][t] >>, where |
1335 | C<I<number>> is the file descriptor number you want to write to (2 is | |
7916a455 JC |
1336 | default), and the combination of letters specifies that you want |
1337 | information about (m)emory and/or (s)v, optionally with | |
f4750dab TC |
1338 | (t)imestamps. For example, C<PERL_MEM_LOG=1mst> logs all |
1339 | information to stdout. You can write to other opened file descriptors | |
1340 | in a variety of ways: | |
9aa9f499 | 1341 | |
f4750dab | 1342 | $ 3>foo3 PERL_MEM_LOG=3m perl ... |
9aa9f499 | 1343 | |
3d0ae7ba | 1344 | =item PERL_ROOT (specific to the VMS port) |
d74e8afc | 1345 | X<PERL_ROOT> |
3d0ae7ba | 1346 | |
f4750dab | 1347 | A translation-concealed rooted logical name that contains Perl and the |
3d0ae7ba | 1348 | logical device for the @INC path on VMS only. Other logical names that |
f4750dab TC |
1349 | affect Perl on VMS include PERLSHR, PERL_ENV_TABLES, and |
1350 | SYS$TIMEZONE_DIFFERENTIAL, but are optional and discussed further in | |
3d0ae7ba GS |
1351 | L<perlvms> and in F<README.vms> in the Perl source distribution. |
1352 | ||
4ffa73a3 | 1353 | =item PERL_SIGNALS |
d74e8afc | 1354 | X<PERL_SIGNALS> |
4ffa73a3 | 1355 | |
f4750dab TC |
1356 | Available in Perls 5.8.1 and later. If set to C<"unsafe">, the pre-Perl-5.8.0 |
1357 | signal behaviour (which is immediate but unsafe) is restored. If set | |
1358 | to C<safe>, then safe (but deferred) signals are used. See | |
1359 | L<perlipc/"Deferred Signals (Safe Signals)">. | |
4ffa73a3 | 1360 | |
a05d7ebb | 1361 | =item PERL_UNICODE |
d74e8afc | 1362 | X<PERL_UNICODE> |
acae81db | 1363 | |
bf61ac64 | 1364 | Equivalent to the B<-C> command-line switch. Note that this is not |
ac036724 | 1365 | a boolean variable. Setting this to C<"1"> is not the right way to |
5b4f334e | 1366 | "enable Unicode" (whatever that would mean). You can use C<"0"> to |
e654d908 | 1367 | "disable Unicode", though (or alternatively unset PERL_UNICODE in |
f4750dab | 1368 | your shell before starting Perl). See the description of the B<-C> |
e654d908 | 1369 | switch for more information. |
acae81db | 1370 | |
3d0ae7ba | 1371 | =item SYS$LOGIN (specific to the VMS port) |
d74e8afc | 1372 | X<SYS$LOGIN> |
3d0ae7ba GS |
1373 | |
1374 | Used if chdir has no argument and HOME and LOGDIR are not set. | |
1375 | ||
a0d0e21e | 1376 | =back |
1e422769 | 1377 | |
1378 | Perl also has environment variables that control how Perl handles data | |
f4750dab TC |
1379 | specific to particular natural languages; see L<perllocale>. |
1380 | ||
1381 | Perl and its various modules and components, including its test frameworks, | |
1382 | may sometimes make use of certain other environment variables. Some of | |
1383 | these are specific to a particular platform. Please consult the | |
1384 | appropriate module documentation and any documentation for your platform | |
1385 | (like L<perlsolaris>, L<perllinux>, L<perlmacosx>, L<perlwin32>, etc) for | |
1386 | variables peculiar to those specific situations. | |
1387 | ||
1388 | Perl makes all environment variables available to the program being | |
1389 | executed, and passes these along to any child processes it starts. | |
1390 | However, programs running setuid would do well to execute the following | |
1391 | lines before doing anything else, just to keep people honest: | |
1392 | ||
1393 | $ENV{PATH} = "/bin:/usr/bin"; # or whatever you need | |
1394 | $ENV{SHELL} = "/bin/sh" if exists $ENV{SHELL}; | |
c90c0ff4 | 1395 | delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; |