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1 | =head1 NAME |
2 | |
3 | perlrun - how to execute the Perl interpreter |
4 | |
5 | =head1 SYNOPSIS |
6 | |
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7 | B<perl> S<[ B<-CsTtuUWX> ]> |
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8 | S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]> |
9 | S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]> |
10 | S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]> |
11 | S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]> |
12 | S<[ B<-P> ]> |
13 | S<[ B<-S> ]> |
14 | S<[ B<-x>[I<dir>] ]> |
15 | S<[ B<-i>[I<extension>] ]> |
16 | S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...> |
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17 | |
18 | =head1 DESCRIPTION |
19 | |
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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 |
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25 | places: |
26 | |
27 | =over 4 |
28 | |
29 | =item 1. |
30 | |
31 | Specified line by line via B<-e> switches on the command line. |
32 | |
33 | =item 2. |
34 | |
35 | Contained in the file specified by the first filename on the command line. |
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36 | (Note that systems supporting the #! notation invoke interpreters this |
37 | way. See L<Location of Perl>.) |
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38 | |
39 | =item 3. |
40 | |
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41 | Passed in implicitly via standard input. This works only if there are |
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42 | no filename arguments--to pass arguments to a STDIN-read program you |
43 | must explicitly specify a "-" for the program name. |
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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 |
49 | scans for the first line starting with #! and containing the word |
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50 | "perl", and starts there instead. This is useful for running a program |
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51 | embedded in a larger message. (In this case you would indicate the end |
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52 | of the program using the C<__END__> token.) |
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53 | |
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54 | The #! line is always examined for switches as the line is being |
55 | parsed. Thus, if you're on a machine that allows only one argument |
56 | with the #! line, or worse, doesn't even recognize the #! line, you |
57 | still can get consistent switch behavior regardless of how Perl was |
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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 |
61 | kernel interpretation of the #! line after 32 characters, some |
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 |
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69 | could also cause odd results. |
70 | |
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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"; }>. |
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75 | |
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76 | Parsing of the #! switches starts wherever "perl" is mentioned in the line. |
77 | The sequences "-*" and "- " are specifically ignored so that you could, |
78 | if you were so inclined, say |
79 | |
80 | #!/bin/sh -- # -*- perl -*- -p |
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81 | eval 'exec perl -wS $0 ${1+"$@"}' |
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82 | if $running_under_some_shell; |
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83 | |
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84 | to let Perl see the B<-p> switch. |
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85 | |
86 | A similar trick involves the B<env> program, if you have it. |
87 | |
88 | #!/usr/bin/env perl |
89 | |
90 | The examples above use a relative path to the perl interpreter, |
91 | getting whatever version is first in the user's path. If you want |
92 | a specific version of Perl, say, perl5.005_57, you should place |
93 | that directly in the #! line's path. |
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94 | |
95 | If the #! line does not contain the word "perl", the program named after |
96 | the #! is executed instead of the Perl interpreter. This is slightly |
97 | bizarre, but it helps people on machines that don't do #!, because they |
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98 | can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then |
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99 | dispatch the program to the correct interpreter for them. |
100 | |
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101 | After locating your program, Perl compiles the entire program to an |
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102 | internal form. If there are any compilation errors, execution of the |
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103 | program is not attempted. (This is unlike the typical shell script, |
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104 | which might run part-way through before finding a syntax error.) |
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105 | |
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106 | If the program is syntactically correct, it is executed. If the program |
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107 | runs off the end without hitting an exit() or die() operator, an implicit |
108 | C<exit(0)> is provided to indicate successful completion. |
109 | |
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110 | =head2 #! and quoting on non-Unix systems |
111 | |
112 | Unix's #! technique can be simulated on other systems: |
113 | |
114 | =over 4 |
115 | |
116 | =item OS/2 |
117 | |
118 | Put |
119 | |
120 | extproc perl -S -your_switches |
121 | |
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122 | as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's |
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123 | `extproc' handling). |
124 | |
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125 | =item MS-DOS |
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126 | |
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127 | Create a batch file to run your program, and codify it in |
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128 | C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source |
129 | distribution for more information). |
130 | |
131 | =item Win95/NT |
132 | |
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133 | The Win95/NT installation, when using the ActiveState installer for Perl, |
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134 | will modify the Registry to associate the F<.pl> extension with the perl |
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135 | interpreter. If you install Perl by other means (including building from |
136 | the sources), you may have to modify the Registry yourself. Note that |
137 | this means you can no longer tell the difference between an executable |
138 | Perl program and a Perl library file. |
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139 | |
140 | =item Macintosh |
141 | |
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142 | A Macintosh perl program will have the appropriate Creator and |
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143 | Type, so that double-clicking them will invoke the perl application. |
144 | |
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145 | =item VMS |
146 | |
147 | Put |
148 | |
149 | $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' ! |
150 | $ exit++ + ++$status != 0 and $exit = $status = undef; |
151 | |
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152 | at the top of your program, where B<-mysw> are any command line switches you |
153 | want to pass to Perl. You can now invoke the program directly, by saying |
154 | C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly |
155 | via F<DCL$PATH> by just using the name of the program). |
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156 | |
157 | This incantation is a bit much to remember, but Perl will display it for |
158 | you if you say C<perl "-V:startperl">. |
159 | |
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160 | =back |
161 | |
162 | Command-interpreters on non-Unix systems have rather different ideas |
163 | on quoting than Unix shells. You'll need to learn the special |
164 | characters in your command-interpreter (C<*>, C<\> and C<"> are |
165 | common) and how to protect whitespace and these characters to run |
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166 | one-liners (see B<-e> below). |
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167 | |
168 | On some systems, you may have to change single-quotes to double ones, |
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169 | which you must I<not> do on Unix or Plan9 systems. You might also |
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170 | have to change a single % to a %%. |
171 | |
172 | For example: |
173 | |
174 | # Unix |
175 | perl -e 'print "Hello world\n"' |
176 | |
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177 | # MS-DOS, etc. |
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178 | perl -e "print \"Hello world\n\"" |
179 | |
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180 | # Macintosh |
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181 | print "Hello world\n" |
182 | (then Run "Myscript" or Shift-Command-R) |
183 | |
184 | # VMS |
185 | perl -e "print ""Hello world\n""" |
186 | |
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187 | The problem is that none of this is reliable: it depends on the |
188 | command and it is entirely possible neither works. If B<4DOS> were |
189 | the command shell, this would probably work better: |
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190 | |
191 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
192 | |
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193 | B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in |
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194 | when nobody was looking, but just try to find documentation for its |
195 | quoting rules. |
196 | |
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197 | Under the Macintosh, it depends which environment you are using. The MacPerl |
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198 | shell, or MPW, is much like Unix shells in its support for several |
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199 | quoting variants, except that it makes free use of the Macintosh's non-ASCII |
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200 | characters as control characters. |
201 | |
202 | There is no general solution to all of this. It's just a mess. |
203 | |
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204 | =head2 Location of Perl |
205 | |
206 | It may seem obvious to say, but Perl is useful only when users can |
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207 | easily find it. When possible, it's good for both F</usr/bin/perl> |
208 | and F</usr/local/bin/perl> to be symlinks to the actual binary. If |
209 | that can't be done, system administrators are strongly encouraged |
210 | to put (symlinks to) perl and its accompanying utilities into a |
211 | directory typically found along a user's PATH, or in some other |
212 | obvious and convenient place. |
213 | |
214 | In this documentation, C<#!/usr/bin/perl> on the first line of the program |
215 | will stand in for whatever method works on your system. You are |
216 | advised to use a specific path if you care about a specific version. |
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217 | |
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218 | #!/usr/local/bin/perl5.00554 |
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219 | |
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220 | or if you just want to be running at least version, place a statement |
221 | like this at the top of your program: |
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222 | |
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223 | use 5.005_54; |
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224 | |
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225 | =head2 Command Switches |
226 | |
227 | As with all standard commands, a single-character switch may be |
228 | clustered with the following switch, if any. |
229 | |
230 | #!/usr/bin/perl -spi.orig # same as -s -p -i.orig |
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231 | |
232 | Switches include: |
233 | |
234 | =over 5 |
235 | |
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236 | =item B<-0>[I<digits>] |
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237 | |
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238 | specifies the input record separator (C<$/>) as an octal number. If there are |
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239 | no digits, the null character is the separator. Other switches may |
240 | precede or follow the digits. For example, if you have a version of |
241 | B<find> which can print filenames terminated by the null character, you |
242 | can say this: |
243 | |
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244 | find . -name '*.orig' -print0 | perl -n0e unlink |
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245 | |
246 | The special value 00 will cause Perl to slurp files in paragraph mode. |
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247 | The value 0777 will cause Perl to slurp files whole because there is no |
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248 | legal character with that value. |
249 | |
250 | =item B<-a> |
251 | |
252 | turns on autosplit mode when used with a B<-n> or B<-p>. An implicit |
253 | split command to the @F array is done as the first thing inside the |
254 | implicit while loop produced by the B<-n> or B<-p>. |
255 | |
256 | perl -ane 'print pop(@F), "\n";' |
257 | |
258 | is equivalent to |
259 | |
260 | while (<>) { |
261 | @F = split(' '); |
262 | print pop(@F), "\n"; |
263 | } |
264 | |
265 | An alternate delimiter may be specified using B<-F>. |
266 | |
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267 | =item B<-C> |
268 | |
269 | enables Perl to use the native wide character APIs on the target system. |
270 | The magic variable C<${^WIDE_SYSTEM_CALLS}> reflects the state of |
271 | this switch. See L<perlvar/"${^WIDE_SYSTEM_CALLS}">. |
272 | |
273 | This feature is currently only implemented on the Win32 platform. |
274 | |
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275 | =item B<-c> |
276 | |
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277 | causes Perl to check the syntax of the program and then exit without |
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278 | executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and |
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279 | C<use> blocks, because these are considered as occurring outside the |
280 | execution of your program. C<INIT> and C<END> blocks, however, will |
281 | be skipped. |
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282 | |
283 | =item B<-d> |
284 | |
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285 | runs the program under the Perl debugger. See L<perldebug>. |
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286 | |
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287 | =item B<-d:>I<foo[=bar,baz]> |
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288 | |
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289 | runs the program under the control of a debugging, profiling, or |
290 | tracing module installed as Devel::foo. E.g., B<-d:DProf> executes |
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291 | the program using the Devel::DProf profiler. As with the B<-M> |
292 | flag, options may be passed to the Devel::foo package where they |
293 | will be received and interpreted by the Devel::foo::import routine. |
294 | The comma-separated list of options must follow a C<=> character. |
295 | See L<perldebug>. |
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296 | |
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297 | =item B<-D>I<letters> |
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298 | |
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299 | =item B<-D>I<number> |
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300 | |
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301 | sets debugging flags. To watch how it executes your program, use |
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302 | B<-Dtls>. (This works only if debugging is compiled into your |
303 | Perl.) Another nice value is B<-Dx>, which lists your compiled |
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304 | syntax tree. And B<-Dr> displays compiled regular expressions; |
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305 | the format of the output is explained in L<perldebguts>. |
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306 | |
307 | As an alternative, specify a number instead of list of letters (e.g., |
308 | B<-D14> is equivalent to B<-Dtls>): |
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309 | |
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310 | 1 p Tokenizing and parsing |
311 | 2 s Stack snapshots |
312 | 4 l Context (loop) stack processing |
313 | 8 t Trace execution |
314 | 16 o Method and overloading resolution |
315 | 32 c String/numeric conversions |
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316 | 64 P Print profiling info, preprocessor command for -P, source file input state |
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317 | 128 m Memory allocation |
318 | 256 f Format processing |
319 | 512 r Regular expression parsing and execution |
320 | 1024 x Syntax tree dump |
321 | 2048 u Tainting checks |
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322 | 4096 L Memory leaks (needs -DLEAKTEST when compiling Perl) |
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323 | 8192 H Hash dump -- usurps values() |
324 | 16384 X Scratchpad allocation |
325 | 32768 D Cleaning up |
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326 | 65536 S Thread synchronization |
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327 | 131072 T Tokenising |
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328 | 262144 R Include reference counts of dumped variables (eg when using -Ds) |
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329 | 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB |
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330 | |
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331 | All these flags require B<-DDEBUGGING> when you compile the Perl |
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332 | executable (but see L<Devel::Peek>, L<re> which may change this). |
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333 | See the F<INSTALL> file in the Perl source distribution |
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334 | for how to do this. This flag is automatically set if you include B<-g> |
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335 | option when C<Configure> asks you about optimizer/debugger flags. |
336 | |
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337 | If you're just trying to get a print out of each line of Perl code |
338 | as it executes, the way that C<sh -x> provides for shell scripts, |
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339 | you can't use Perl's B<-D> switch. Instead do this |
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340 | |
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341 | # If you have "env" utility |
342 | env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program |
343 | |
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344 | # Bourne shell syntax |
345 | $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program |
346 | |
347 | # csh syntax |
348 | % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program) |
349 | |
350 | See L<perldebug> for details and variations. |
351 | |
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352 | =item B<-e> I<commandline> |
353 | |
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354 | may be used to enter one line of program. If B<-e> is given, Perl |
355 | will not look for a filename in the argument list. Multiple B<-e> |
356 | commands may be given to build up a multi-line script. Make sure |
357 | to use semicolons where you would in a normal program. |
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358 | |
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359 | =item B<-F>I<pattern> |
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360 | |
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361 | specifies the pattern to split on if B<-a> is also in effect. The |
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362 | pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be |
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363 | put in single quotes. |
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364 | |
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365 | =item B<-h> |
366 | |
367 | prints a summary of the options. |
368 | |
369 | =item B<-i>[I<extension>] |
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370 | |
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371 | specifies that files processed by the C<E<lt>E<gt>> construct are to be |
372 | edited in-place. It does this by renaming the input file, opening the |
373 | output file by the original name, and selecting that output file as the |
374 | default for print() statements. The extension, if supplied, is used to |
375 | modify the name of the old file to make a backup copy, following these |
376 | rules: |
377 | |
378 | If no extension is supplied, no backup is made and the current file is |
379 | overwritten. |
380 | |
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381 | If the extension doesn't contain a C<*>, then it is appended to the |
382 | end of the current filename as a suffix. If the extension does |
383 | contain one or more C<*> characters, then each C<*> is replaced |
384 | with the current filename. In Perl terms, you could think of this |
385 | as: |
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386 | |
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387 | ($backup = $extension) =~ s/\*/$file_name/g; |
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388 | |
389 | This allows you to add a prefix to the backup file, instead of (or in |
390 | addition to) a suffix: |
391 | |
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392 | $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA' |
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393 | |
394 | Or even to place backup copies of the original files into another |
395 | directory (provided the directory already exists): |
396 | |
19799a22 |
397 | $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig' |
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398 | |
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399 | These sets of one-liners are equivalent: |
400 | |
401 | $ perl -pi -e 's/bar/baz/' fileA # overwrite current file |
19799a22 |
402 | $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file |
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403 | |
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404 | $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' |
405 | $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' |
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406 | |
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407 | From the shell, saying |
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408 | |
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409 | $ perl -p -i.orig -e "s/foo/bar/; ... " |
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410 | |
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411 | is the same as using the program: |
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412 | |
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413 | #!/usr/bin/perl -pi.orig |
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414 | s/foo/bar/; |
415 | |
416 | which is equivalent to |
417 | |
418 | #!/usr/bin/perl |
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419 | $extension = '.orig'; |
420 | LINE: while (<>) { |
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421 | if ($ARGV ne $oldargv) { |
66606d78 |
422 | if ($extension !~ /\*/) { |
423 | $backup = $ARGV . $extension; |
424 | } |
425 | else { |
426 | ($backup = $extension) =~ s/\*/$ARGV/g; |
427 | } |
428 | rename($ARGV, $backup); |
a0d0e21e |
429 | open(ARGVOUT, ">$ARGV"); |
430 | select(ARGVOUT); |
431 | $oldargv = $ARGV; |
432 | } |
433 | s/foo/bar/; |
434 | } |
435 | continue { |
436 | print; # this prints to original filename |
437 | } |
438 | select(STDOUT); |
439 | |
440 | except that the B<-i> form doesn't need to compare $ARGV to $oldargv to |
441 | know when the filename has changed. It does, however, use ARGVOUT for |
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442 | the selected filehandle. Note that STDOUT is restored as the default |
443 | output filehandle after the loop. |
444 | |
445 | As shown above, Perl creates the backup file whether or not any output |
446 | is actually changed. So this is just a fancy way to copy files: |
447 | |
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448 | $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3... |
449 | or |
450 | $ perl -p -i '.orig' -e 1 file1 file2 file3... |
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451 | |
452 | You can use C<eof> without parentheses to locate the end of each input |
453 | file, in case you want to append to each file, or reset line numbering |
454 | (see example in L<perlfunc/eof>). |
455 | |
456 | If, for a given file, Perl is unable to create the backup file as |
457 | specified in the extension then it will skip that file and continue on |
458 | with the next one (if it exists). |
459 | |
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460 | For a discussion of issues surrounding file permissions and B<-i>, |
cea6626f |
461 | see L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>. |
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462 | |
463 | You cannot use B<-i> to create directories or to strip extensions from |
464 | files. |
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465 | |
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466 | Perl does not expand C<~> in filenames, which is good, since some |
467 | folks use it for their backup files: |
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468 | |
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469 | $ perl -pi~ -e 's/foo/bar/' file1 file2 file3... |
470 | |
471 | Finally, the B<-i> switch does not impede execution when no |
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472 | files are given on the command line. In this case, no backup is made |
473 | (the original file cannot, of course, be determined) and processing |
474 | proceeds from STDIN to STDOUT as might be expected. |
475 | |
a0d0e21e |
476 | =item B<-I>I<directory> |
477 | |
e0ebc809 |
478 | Directories specified by B<-I> are prepended to the search path for |
1fef88e7 |
479 | modules (C<@INC>), and also tells the C preprocessor where to search for |
e0ebc809 |
480 | include files. The C preprocessor is invoked with B<-P>; by default it |
481 | searches /usr/include and /usr/lib/perl. |
a0d0e21e |
482 | |
e0ebc809 |
483 | =item B<-l>[I<octnum>] |
a0d0e21e |
484 | |
19799a22 |
485 | enables automatic line-ending processing. It has two separate |
486 | effects. First, it automatically chomps C<$/> (the input record |
487 | separator) when used with B<-n> or B<-p>. Second, it assigns C<$\> |
488 | (the output record separator) to have the value of I<octnum> so |
489 | that any print statements will have that separator added back on. |
490 | If I<octnum> is omitted, sets C<$\> to the current value of |
491 | C<$/>. For instance, to trim lines to 80 columns: |
a0d0e21e |
492 | |
493 | perl -lpe 'substr($_, 80) = ""' |
494 | |
495 | Note that the assignment C<$\ = $/> is done when the switch is processed, |
496 | so the input record separator can be different than the output record |
497 | separator if the B<-l> switch is followed by a B<-0> switch: |
498 | |
499 | gnufind / -print0 | perl -ln0e 'print "found $_" if -p' |
500 | |
1fef88e7 |
501 | This sets C<$\> to newline and then sets C<$/> to the null character. |
a0d0e21e |
502 | |
e0ebc809 |
503 | =item B<-m>[B<->]I<module> |
504 | |
505 | =item B<-M>[B<->]I<module> |
c07a80fd |
506 | |
e0ebc809 |
507 | =item B<-M>[B<->]I<'module ...'> |
508 | |
509 | =item B<-[mM]>[B<->]I<module=arg[,arg]...> |
3c81428c |
510 | |
19799a22 |
511 | B<-m>I<module> executes C<use> I<module> C<();> before executing your |
512 | program. |
3c81428c |
513 | |
19799a22 |
514 | B<-M>I<module> executes C<use> I<module> C<;> before executing your |
515 | program. You can use quotes to add extra code after the module name, |
516 | e.g., C<'-Mmodule qw(foo bar)'>. |
3c81428c |
517 | |
19799a22 |
518 | If the first character after the B<-M> or B<-m> is a dash (C<->) |
a5f75d66 |
519 | then the 'use' is replaced with 'no'. |
520 | |
54310121 |
521 | A little builtin syntactic sugar means you can also say |
19799a22 |
522 | B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for |
523 | C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when |
524 | importing symbols. The actual code generated by B<-Mmodule=foo,bar> is |
e0ebc809 |
525 | C<use module split(/,/,q{foo,bar})>. Note that the C<=> form |
19799a22 |
526 | removes the distinction between B<-m> and B<-M>. |
3c81428c |
527 | |
a0d0e21e |
528 | =item B<-n> |
529 | |
19799a22 |
530 | causes Perl to assume the following loop around your program, which |
a0d0e21e |
531 | makes it iterate over filename arguments somewhat like B<sed -n> or |
532 | B<awk>: |
533 | |
19799a22 |
534 | LINE: |
a0d0e21e |
535 | while (<>) { |
19799a22 |
536 | ... # your program goes here |
a0d0e21e |
537 | } |
538 | |
539 | Note that the lines are not printed by default. See B<-p> to have |
08e9d68e |
540 | lines printed. If a file named by an argument cannot be opened for |
19799a22 |
541 | some reason, Perl warns you about it and moves on to the next file. |
08e9d68e |
542 | |
543 | Here is an efficient way to delete all files older than a week: |
a0d0e21e |
544 | |
19799a22 |
545 | find . -mtime +7 -print | perl -nle unlink |
a0d0e21e |
546 | |
19799a22 |
547 | This is faster than using the B<-exec> switch of B<find> because you don't |
548 | have to start a process on every filename found. It does suffer from |
549 | the bug of mishandling newlines in pathnames, which you can fix if |
44a4342c |
550 | you follow the example under B<-0>. |
a0d0e21e |
551 | |
552 | C<BEGIN> and C<END> blocks may be used to capture control before or after |
19799a22 |
553 | the implicit program loop, just as in B<awk>. |
a0d0e21e |
554 | |
555 | =item B<-p> |
556 | |
19799a22 |
557 | causes Perl to assume the following loop around your program, which |
a0d0e21e |
558 | makes it iterate over filename arguments somewhat like B<sed>: |
559 | |
560 | |
19799a22 |
561 | LINE: |
a0d0e21e |
562 | while (<>) { |
19799a22 |
563 | ... # your program goes here |
a0d0e21e |
564 | } continue { |
08e9d68e |
565 | print or die "-p destination: $!\n"; |
a0d0e21e |
566 | } |
567 | |
08e9d68e |
568 | If a file named by an argument cannot be opened for some reason, Perl |
569 | warns you about it, and moves on to the next file. Note that the |
c2611fb3 |
570 | lines are printed automatically. An error occurring during printing is |
08e9d68e |
571 | treated as fatal. To suppress printing use the B<-n> switch. A B<-p> |
572 | overrides a B<-n> switch. |
a0d0e21e |
573 | |
574 | C<BEGIN> and C<END> blocks may be used to capture control before or after |
19799a22 |
575 | the implicit loop, just as in B<awk>. |
a0d0e21e |
576 | |
577 | =item B<-P> |
578 | |
079a94c4 |
579 | B<NOTE: Use of -P is strongly discouraged because of its inherent |
580 | problems, including poor portability.> |
581 | |
582 | This option causes your program to be run through the C preprocessor before |
efdf3af0 |
583 | compilation by Perl. Because both comments and B<cpp> directives begin |
a0d0e21e |
584 | with the # character, you should avoid starting comments with any words |
efdf3af0 |
585 | recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">. |
079a94c4 |
586 | |
587 | If you're considering using C<-P>, you might also want to look at the |
588 | Filter::cpp module from CPAN. |
589 | |
590 | The problems of -P include, but are not limited to: |
591 | |
592 | =over 10 |
593 | |
594 | =item * |
595 | |
596 | The C<#!> line is stripped, so any switches there don't apply. |
597 | |
598 | =item * |
599 | |
600 | A C<-P> on a C<#!> line doesn't work. |
601 | |
602 | =item * |
603 | |
604 | B<All> lines that begin with (whitespace and) a C<#> but |
605 | do not look like cpp commands, are stripped, including anything |
44a4342c |
606 | inside Perl strings, regular expressions, and here-docs . |
079a94c4 |
607 | |
608 | =item * |
609 | |
610 | In some platforms the C preprocessor knows too much: it knows about |
611 | the C++ -style until-end-of-line comments starting with C<"//">. |
efdf3af0 |
612 | This will cause problems with common Perl constructs like |
613 | |
614 | s/foo//; |
615 | |
616 | because after -P this will became illegal code |
617 | |
618 | s/foo |
619 | |
620 | The workaround is to use some other quoting separator than C<"/">, |
621 | like for example C<"!">: |
622 | |
623 | s!foo!!; |
a0d0e21e |
624 | |
079a94c4 |
625 | |
626 | |
627 | =item * |
628 | |
629 | It requires not only a working C preprocessor but also a working |
630 | F<sed>. If not on UNIX, you are probably out of luck on this. |
631 | |
632 | =item * |
633 | |
634 | Script line numbers are not preserved. |
635 | |
636 | =item * |
637 | |
638 | The C<-x> does not work with C<-P>. |
639 | |
640 | =back |
9a1f07e7 |
641 | |
a0d0e21e |
642 | =item B<-s> |
643 | |
19799a22 |
644 | enables rudimentary switch parsing for switches on the command |
645 | line after the program name but before any filename arguments (or before |
3bbcc830 |
646 | an argument of B<-->). This means you can have switches with two leading |
647 | dashes (B<--help>). Any switch found there is removed from @ARGV and sets the |
19799a22 |
648 | corresponding variable in the Perl program. The following program |
3c0facb2 |
649 | prints "1" if the program is invoked with a B<-xyz> switch, and "abc" |
650 | if it is invoked with B<-xyz=abc>. |
a0d0e21e |
651 | |
652 | #!/usr/bin/perl -s |
3c0facb2 |
653 | if ($xyz) { print "$xyz\n" } |
a0d0e21e |
654 | |
3bbcc830 |
655 | Do note that B<--help> creates the variable ${-help}, which is not compliant |
656 | with C<strict refs>. |
657 | |
a0d0e21e |
658 | =item B<-S> |
659 | |
660 | makes Perl use the PATH environment variable to search for the |
19799a22 |
661 | program (unless the name of the program contains directory separators). |
662 | |
2a92aaa0 |
663 | On some platforms, this also makes Perl append suffixes to the |
664 | filename while searching for it. For example, on Win32 platforms, |
665 | the ".bat" and ".cmd" suffixes are appended if a lookup for the |
666 | original name fails, and if the name does not already end in one |
667 | of those suffixes. If your Perl was compiled with DEBUGGING turned |
668 | on, using the -Dp switch to Perl shows how the search progresses. |
669 | |
2a92aaa0 |
670 | Typically this is used to emulate #! startup on platforms that |
671 | don't support #!. This example works on many platforms that |
672 | have a shell compatible with Bourne shell: |
a0d0e21e |
673 | |
674 | #!/usr/bin/perl |
a3cb178b |
675 | eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}' |
a0d0e21e |
676 | if $running_under_some_shell; |
677 | |
19799a22 |
678 | The system ignores the first line and feeds the program to F</bin/sh>, |
679 | which proceeds to try to execute the Perl program as a shell script. |
a0d0e21e |
680 | The shell executes the second line as a normal shell command, and thus |
681 | starts up the Perl interpreter. On some systems $0 doesn't always |
682 | contain the full pathname, so the B<-S> tells Perl to search for the |
19799a22 |
683 | program if necessary. After Perl locates the program, it parses the |
a0d0e21e |
684 | lines and ignores them because the variable $running_under_some_shell |
19799a22 |
685 | is never true. If the program will be interpreted by csh, you will need |
a3cb178b |
686 | to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand |
687 | embedded spaces (and such) in the argument list. To start up sh rather |
a0d0e21e |
688 | than csh, some systems may have to replace the #! line with a line |
689 | containing just a colon, which will be politely ignored by Perl. Other |
690 | systems can't control that, and need a totally devious construct that |
19799a22 |
691 | will work under any of B<csh>, B<sh>, or Perl, such as the following: |
a0d0e21e |
692 | |
19799a22 |
693 | eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}' |
a3cb178b |
694 | & eval 'exec /usr/bin/perl -wS $0 $argv:q' |
5f05dabc |
695 | if $running_under_some_shell; |
a0d0e21e |
696 | |
19799a22 |
697 | If the filename supplied contains directory separators (i.e., is an |
698 | absolute or relative pathname), and if that file is not found, |
699 | platforms that append file extensions will do so and try to look |
700 | for the file with those extensions added, one by one. |
701 | |
702 | On DOS-like platforms, if the program does not contain directory |
703 | separators, it will first be searched for in the current directory |
704 | before being searched for on the PATH. On Unix platforms, the |
705 | program will be searched for strictly on the PATH. |
706 | |
6537fe72 |
707 | =item B<-t> |
708 | |
709 | Like B<-T>, but taint checks will issue warnings rather than fatal |
317ea90d |
710 | errors. These warnings can be controlled normally with C<no warnings |
711 | qw(taint)>. |
1dbad523 |
712 | |
713 | B<NOTE: this is not a substitute for -T.> This is meant only to be |
714 | used as a temporary development aid while securing legacy code: |
715 | for real production code and for new secure code written from scratch |
716 | always use the real B<-T>. |
6537fe72 |
717 | |
a0d0e21e |
718 | =item B<-T> |
719 | |
a3cb178b |
720 | forces "taint" checks to be turned on so you can test them. Ordinarily |
19799a22 |
721 | these checks are done only when running setuid or setgid. It's a |
722 | good idea to turn them on explicitly for programs that run on behalf |
723 | of someone else whom you might not necessarily trust, such as CGI |
724 | programs or any internet servers you might write in Perl. See |
725 | L<perlsec> for details. For security reasons, this option must be |
726 | seen by Perl quite early; usually this means it must appear early |
727 | on the command line or in the #! line for systems which support |
728 | that construct. |
a0d0e21e |
729 | |
730 | =item B<-u> |
731 | |
19799a22 |
732 | This obsolete switch causes Perl to dump core after compiling your |
733 | program. You can then in theory take this core dump and turn it |
734 | into an executable file by using the B<undump> program (not supplied). |
735 | This speeds startup at the expense of some disk space (which you |
736 | can minimize by stripping the executable). (Still, a "hello world" |
737 | executable comes out to about 200K on my machine.) If you want to |
738 | execute a portion of your program before dumping, use the dump() |
739 | operator instead. Note: availability of B<undump> is platform |
740 | specific and may not be available for a specific port of Perl. |
741 | |
742 | This switch has been superseded in favor of the new Perl code |
743 | generator backends to the compiler. See L<B> and L<B::Bytecode> |
744 | for details. |
a0d0e21e |
745 | |
746 | =item B<-U> |
747 | |
748 | allows Perl to do unsafe operations. Currently the only "unsafe" |
749 | operations are the unlinking of directories while running as superuser, |
750 | and running setuid programs with fatal taint checks turned into |
19799a22 |
751 | warnings. Note that the B<-w> switch (or the C<$^W> variable) must |
752 | be used along with this option to actually I<generate> the |
fb73857a |
753 | taint-check warnings. |
a0d0e21e |
754 | |
755 | =item B<-v> |
756 | |
19799a22 |
757 | prints the version and patchlevel of your perl executable. |
a0d0e21e |
758 | |
3c81428c |
759 | =item B<-V> |
760 | |
761 | prints summary of the major perl configuration values and the current |
19799a22 |
762 | values of @INC. |
3c81428c |
763 | |
e0ebc809 |
764 | =item B<-V:>I<name> |
3c81428c |
765 | |
766 | Prints to STDOUT the value of the named configuration variable. |
44a4342c |
767 | For example, |
3c81428c |
768 | |
19799a22 |
769 | $ perl -V:man.dir |
770 | |
771 | will provide strong clues about what your MANPATH variable should |
772 | be set to in order to access the Perl documentation. |
a0d0e21e |
773 | |
19799a22 |
774 | =item B<-w> |
774d564b |
775 | |
19799a22 |
776 | prints warnings about dubious constructs, such as variable names |
777 | that are mentioned only once and scalar variables that are used |
778 | before being set, redefined subroutines, references to undefined |
779 | filehandles or filehandles opened read-only that you are attempting |
780 | to write on, values used as a number that doesn't look like numbers, |
781 | using an array as though it were a scalar, if your subroutines |
782 | recurse more than 100 deep, and innumerable other things. |
783 | |
784 | This switch really just enables the internal C<^$W> variable. You |
785 | can disable or promote into fatal errors specific warnings using |
786 | C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>. |
787 | See also L<perldiag> and L<perltrap>. A new, fine-grained warning |
788 | facility is also available if you want to manipulate entire classes |
9f1b1f2d |
789 | of warnings; see L<warnings> or L<perllexwarn>. |
a0d0e21e |
790 | |
0453d815 |
791 | =item B<-W> |
792 | |
3c0facb2 |
793 | Enables all warnings regardless of C<no warnings> or C<$^W>. |
0453d815 |
794 | See L<perllexwarn>. |
795 | |
796 | =item B<-X> |
797 | |
3c0facb2 |
798 | Disables all warnings regardless of C<use warnings> or C<$^W>. |
0453d815 |
799 | See L<perllexwarn>. |
800 | |
a0d0e21e |
801 | =item B<-x> I<directory> |
802 | |
19799a22 |
803 | tells Perl that the program is embedded in a larger chunk of unrelated |
804 | ASCII text, such as in a mail message. Leading garbage will be |
805 | discarded until the first line that starts with #! and contains the |
806 | string "perl". Any meaningful switches on that line will be applied. |
807 | If a directory name is specified, Perl will switch to that directory |
808 | before running the program. The B<-x> switch controls only the |
809 | disposal of leading garbage. The program must be terminated with |
810 | C<__END__> if there is trailing garbage to be ignored (the program |
811 | can process any or all of the trailing garbage via the DATA filehandle |
812 | if desired). |
a0d0e21e |
813 | |
1e422769 |
814 | =back |
815 | |
816 | =head1 ENVIRONMENT |
817 | |
818 | =over 12 |
819 | |
820 | =item HOME |
821 | |
822 | Used if chdir has no argument. |
823 | |
824 | =item LOGDIR |
825 | |
826 | Used if chdir has no argument and HOME is not set. |
827 | |
828 | =item PATH |
829 | |
19799a22 |
830 | Used in executing subprocesses, and in finding the program if B<-S> is |
1e422769 |
831 | used. |
832 | |
833 | =item PERL5LIB |
834 | |
835 | A colon-separated list of directories in which to look for Perl library |
836 | files before looking in the standard library and the current |
951ba7fe |
837 | directory. Any architecture-specific directories under the specified |
838 | locations are automatically included if they exist. If PERL5LIB is not |
839 | defined, PERLLIB is used. |
840 | |
841 | When running taint checks (either because the program was running setuid |
842 | or setgid, or the B<-T> switch was used), neither variable is used. |
843 | The program should instead say: |
1e422769 |
844 | |
845 | use lib "/my/directory"; |
846 | |
54310121 |
847 | =item PERL5OPT |
848 | |
849 | Command-line options (switches). Switches in this variable are taken |
1c4db469 |
850 | as if they were on every Perl command line. Only the B<-[DIMUdmtw]> |
19799a22 |
851 | switches are allowed. When running taint checks (because the program |
54310121 |
852 | was running setuid or setgid, or the B<-T> switch was used), this |
74288ac8 |
853 | variable is ignored. If PERL5OPT begins with B<-T>, tainting will be |
854 | enabled, and any subsequent options ignored. |
54310121 |
855 | |
16537909 |
856 | =item PERLIO |
857 | |
44a4342c |
858 | A space (or colon) separated list of PerlIO layers. If perl is built |
859 | to use PerlIO system for IO (the default) these layers effect perl's IO. |
860 | |
861 | It is conventional to start layer names with a colon e.g. C<:perlio> to |
862 | emphasise their similarity to variable "attributes". But the code that parses |
863 | layer specification strings (which is also used to decode the PERLIO |
864 | environment variable) treats the colon as a separator. |
865 | |
866 | The list becomes the default for I<all> perl's IO. Consequently only built-in |
867 | layers can appear in this list, as external layers (such as :encoding()) need |
868 | IO in order to load them!. See L<"open pragma"|open> for how to add external |
869 | encodings as defaults. |
870 | |
871 | The layers that it makes sense to include in the PERLIO environment |
872 | variable are summarised below. For more details see L<PerlIO>. |
16537909 |
873 | |
874 | =over 8 |
875 | |
876 | =item :bytes |
877 | |
44a4342c |
878 | Turns I<off> the C<:utf8> flag for the layer below. |
99366417 |
879 | Unlikely to be useful in global PERLIO environment variable. |
16537909 |
880 | |
881 | =item :crlf |
882 | |
44a4342c |
883 | A layer that implements DOS/Windows like CRLF line endings. |
884 | On read converts pairs of CR,LF to a single "\n" newline character. |
885 | On write converts each "\n" to a CR,LF pair. |
886 | Based on the C<:perlio> layer. |
887 | |
888 | =item :mmap |
889 | |
890 | A layer which implements "reading" of files by using C<mmap()> to |
891 | make (whole) file appear in the process's address space, and then |
892 | using that as PerlIO's "buffer". This I<may> be faster in certain |
893 | circumstances for large files, and may result in less physical memory |
894 | use when multiple processes are reading the same file. |
16537909 |
895 | |
44a4342c |
896 | Files which are not C<mmap()>-able revert to behaving like the C<:perlio> |
897 | layer. Writes also behave like C<:perlio> layer as C<mmap()> for write |
898 | needs extra house-keeping (to extend the file) which negates any advantage. |
16537909 |
899 | |
44a4342c |
900 | The C<:mmap> layer will not exist if platform does not support C<mmap()>. |
16537909 |
901 | |
44a4342c |
902 | =item :perlio |
16537909 |
903 | |
44a4342c |
904 | A from scratch implementation of buffering for PerlIO. Provides fast |
905 | access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt> |
906 | and in general attempts to minimize data copying. |
16537909 |
907 | |
44a4342c |
908 | C<:perlio> will insert a C<:unix> layer below itself to do low level IO. |
16537909 |
909 | |
44a4342c |
910 | =item :raw |
16537909 |
911 | |
44a4342c |
912 | Arranges for all accesses go straight to the lowest level layer provided |
913 | by the configration. That is it strips off any layers above that layer. |
914 | (The intent - unless layers are then pushed on top again - |
915 | is to make perl's C<read> behave like C<sysread>.) |
16537909 |
916 | |
44a4342c |
917 | Not really useful in PERLIO environment variable, instead just use C<:unix> |
918 | layer explicitly. |
16537909 |
919 | |
44a4342c |
920 | In perl5.6 and some books the C<:raw> layer (also called a discipline) is |
921 | documented as the inverse of the C<:crlf> layer. That is not really the case. |
922 | If you want UNIX line endings on a platform that normaly does CRLF translation |
923 | the appropriate thing to do is to add C<:perlio> to PERLIO environment |
924 | variable. |
16537909 |
925 | |
44a4342c |
926 | =item :stdio |
927 | |
928 | This layer provides PerlIO interface by wrapping system's ANSI C "stdio" |
929 | library calls. The layer provides both buffering and IO. |
930 | Note that C<:stdio> layer does I<not> do CRLF translation even if that |
931 | is platforms normal behaviour. You will need a C<:crlf> layer above it |
932 | to do that. |
933 | |
934 | =item :unix |
935 | |
936 | Lowest level layer which provides basic PerlIO operations in terms of |
937 | UNIX/POSIX numeric file descriptor calls |
938 | C<open(), read(), write(), lseek(), close()> |
16537909 |
939 | |
940 | =item :utf8 |
941 | |
44a4342c |
942 | Turns on a flag on the layer below to tell perl that data sent to the |
943 | stream should be converted to perl internal "utf8" form and that data from the |
944 | stream should be considered as so encoded. On ASCII based platforms the |
945 | encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC. |
946 | May be useful in PERLIO environment variable to make UTF-8 the |
947 | default. (To turn off that behaviour use C<:bytes> layer.) |
948 | |
949 | =item :win32 |
950 | |
951 | On Win32 platfroms this I<experimental> layer uses native "handle" IO |
952 | rather than unix-like numeric file descriptor layer. Known to be |
953 | buggy in this release. |
16537909 |
954 | |
955 | =back |
956 | |
44a4342c |
957 | On all platforms the default set of layers should give acceptable results. |
958 | |
959 | For UNIX platfroms that will equivalent of "unix perlio" or "stdio". |
960 | Configure is setup to prefer "stdio" implementation if system's library |
961 | provides for fast access to the buffer, otherwise it uses the "unix perlio" |
962 | implementation. |
963 | |
964 | On Win32 the default in this release is "unix crlf". Win32's "stdio" |
965 | has a number of bugs/mis-features for perl IO which are somewhat |
99366417 |
966 | C compiler vendor/version dependent. Using our own C<crlf> layer as |
44a4342c |
967 | the buffer avoids those issues and makes things more uniform. |
968 | The C<crlf> layer provides CRLF to/from "\n" conversion as well as |
969 | buffering. |
970 | |
971 | This release uses C<unix> as the bottom layer on Win32 and so still uses C |
972 | compiler's numeric file descriptor routines. There is an experimental native |
973 | C<win32> layer which is expected to be enhanced and should eventually replace |
974 | the C<unix> layer. |
975 | |
976 | =item PERLIO_DEBUG |
977 | |
978 | If set to the name of a file or device then certain operations of PerlIO |
979 | sub-system will be logged to that file (opened as append). Typical uses |
980 | are UNIX: |
981 | |
982 | PERLIO_DEBUG=/dev/tty perl script ... |
983 | |
984 | and Win32 approximate equivalent: |
985 | |
986 | set PERLIO_DEBUG=CON |
987 | perl script ... |
988 | |
16537909 |
989 | |
1e422769 |
990 | =item PERLLIB |
991 | |
992 | A colon-separated list of directories in which to look for Perl library |
993 | files before looking in the standard library and the current directory. |
994 | If PERL5LIB is defined, PERLLIB is not used. |
995 | |
996 | =item PERL5DB |
997 | |
998 | The command used to load the debugger code. The default is: |
999 | |
1000 | BEGIN { require 'perl5db.pl' } |
1001 | |
19799a22 |
1002 | =item PERL5SHELL (specific to the Win32 port) |
174c211a |
1003 | |
1004 | May be set to an alternative shell that perl must use internally for |
ce1da67e |
1005 | executing "backtick" commands or system(). Default is C<cmd.exe /x/c> |
1006 | on WindowsNT and C<command.com /c> on Windows95. The value is considered |
19799a22 |
1007 | to be space-separated. Precede any character that needs to be protected |
ce1da67e |
1008 | (like a space or backslash) with a backslash. |
1009 | |
1010 | Note that Perl doesn't use COMSPEC for this purpose because |
1011 | COMSPEC has a high degree of variability among users, leading to |
1012 | portability concerns. Besides, perl can use a shell that may not be |
1013 | fit for interactive use, and setting COMSPEC to such a shell may |
1014 | interfere with the proper functioning of other programs (which usually |
1015 | look in COMSPEC to find a shell fit for interactive use). |
174c211a |
1016 | |
1e422769 |
1017 | =item PERL_DEBUG_MSTATS |
1018 | |
67ce8856 |
1019 | Relevant only if perl is compiled with the malloc included with the perl |
a3cb178b |
1020 | distribution (that is, if C<perl -V:d_mymalloc> is 'define'). |
1021 | If set, this causes memory statistics to be dumped after execution. If set |
1e422769 |
1022 | to an integer greater than one, also causes memory statistics to be dumped |
1023 | after compilation. |
1024 | |
1025 | =item PERL_DESTRUCT_LEVEL |
1026 | |
1027 | Relevant only if your perl executable was built with B<-DDEBUGGING>, |
1028 | this controls the behavior of global destruction of objects and other |
64cea5fd |
1029 | references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information. |
a0d0e21e |
1030 | |
5d170f3a |
1031 | =item PERL_ENCODING |
1032 | |
1033 | If using the C<encoding> pragma without an explicit encoding name, the |
1034 | PERL_ENCODING environment variable is consulted for an encoding name. |
1035 | |
3d0ae7ba |
1036 | =item PERL_ROOT (specific to the VMS port) |
1037 | |
1038 | A translation concealed rooted logical name that contains perl and the |
1039 | logical device for the @INC path on VMS only. Other logical names that |
44a4342c |
1040 | affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and |
1041 | SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in |
3d0ae7ba |
1042 | L<perlvms> and in F<README.vms> in the Perl source distribution. |
1043 | |
1044 | =item SYS$LOGIN (specific to the VMS port) |
1045 | |
1046 | Used if chdir has no argument and HOME and LOGDIR are not set. |
1047 | |
a0d0e21e |
1048 | =back |
1e422769 |
1049 | |
1050 | Perl also has environment variables that control how Perl handles data |
1051 | specific to particular natural languages. See L<perllocale>. |
1052 | |
1053 | Apart from these, Perl uses no other environment variables, except |
19799a22 |
1054 | to make them available to the program being executed, and to child |
1055 | processes. However, programs running setuid would do well to execute |
1e422769 |
1056 | the following lines before doing anything else, just to keep people |
1057 | honest: |
1058 | |
19799a22 |
1059 | $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need |
7bac28a0 |
1060 | $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL}; |
c90c0ff4 |
1061 | delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; |