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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<-sTuU> ]> |
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 | |
20 | Upon startup, Perl looks for your script in one of the following |
21 | places: |
22 | |
23 | =over 4 |
24 | |
25 | =item 1. |
26 | |
27 | Specified line by line via B<-e> switches on the command line. |
28 | |
29 | =item 2. |
30 | |
31 | Contained in the file specified by the first filename on the command line. |
32 | (Note that systems supporting the #! notation invoke interpreters this way.) |
33 | |
34 | =item 3. |
35 | |
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36 | Passed in implicitly via standard input. This works only if there are |
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37 | no filename arguments--to pass arguments to a STDIN script you |
38 | must explicitly specify a "-" for the script name. |
39 | |
40 | =back |
41 | |
42 | With methods 2 and 3, Perl starts parsing the input file from the |
43 | beginning, unless you've specified a B<-x> switch, in which case it |
44 | scans for the first line starting with #! and containing the word |
45 | "perl", and starts there instead. This is useful for running a script |
46 | embedded in a larger message. (In this case you would indicate the end |
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47 | of the script using the C<__END__> token.) |
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48 | |
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49 | The #! line is always examined for switches as the line is being |
50 | parsed. Thus, if you're on a machine that allows only one argument |
51 | with the #! line, or worse, doesn't even recognize the #! line, you |
52 | still can get consistent switch behavior regardless of how Perl was |
53 | invoked, even if B<-x> was used to find the beginning of the script. |
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54 | |
55 | Because many operating systems silently chop off kernel interpretation of |
56 | the #! line after 32 characters, some switches may be passed in on the |
57 | command line, and some may not; you could even get a "-" without its |
58 | letter, if you're not careful. You probably want to make sure that all |
59 | your switches fall either before or after that 32 character boundary. |
60 | Most switches don't actually care if they're processed redundantly, but |
61 | getting a - instead of a complete switch could cause Perl to try to |
62 | execute standard input instead of your script. And a partial B<-I> switch |
63 | could also cause odd results. |
64 | |
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65 | Some switches do care if they are processed twice, for instance combinations |
66 | of B<-l> and B<-0>. Either put all the switches after the 32 character |
67 | boundary (if applicable), or replace the use of B<-0>I<digits> by |
68 | C<BEGIN{ $/ = "\0digits"; }>. |
69 | |
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70 | Parsing of the #! switches starts wherever "perl" is mentioned in the line. |
71 | The sequences "-*" and "- " are specifically ignored so that you could, |
72 | if you were so inclined, say |
73 | |
74 | #!/bin/sh -- # -*- perl -*- -p |
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75 | eval 'exec /usr/bin/perl -S $0 ${1+"$@"}' |
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76 | if $running_under_some_shell; |
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77 | |
78 | to let Perl see the B<-p> switch. |
79 | |
80 | If the #! line does not contain the word "perl", the program named after |
81 | the #! is executed instead of the Perl interpreter. This is slightly |
82 | bizarre, but it helps people on machines that don't do #!, because they |
83 | can tell a program that their SHELL is /usr/bin/perl, and Perl will then |
84 | dispatch the program to the correct interpreter for them. |
85 | |
86 | After locating your script, Perl compiles the entire script to an |
87 | internal form. If there are any compilation errors, execution of the |
88 | script is not attempted. (This is unlike the typical shell script, |
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89 | which might run part-way through before finding a syntax error.) |
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90 | |
91 | If the script is syntactically correct, it is executed. If the script |
92 | runs off the end without hitting an exit() or die() operator, an implicit |
93 | C<exit(0)> is provided to indicate successful completion. |
94 | |
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95 | =head2 #! and quoting on non-Unix systems |
96 | |
97 | Unix's #! technique can be simulated on other systems: |
98 | |
99 | =over 4 |
100 | |
101 | =item OS/2 |
102 | |
103 | Put |
104 | |
105 | extproc perl -S -your_switches |
106 | |
107 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
108 | `extproc' handling). |
109 | |
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110 | =item MS-DOS |
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111 | |
112 | Create a batch file to run your script, and codify it in |
113 | C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source |
114 | distribution for more information). |
115 | |
116 | =item Win95/NT |
117 | |
118 | The Win95/NT installation, when using the Activeware port of Perl, |
119 | will modify the Registry to associate the .pl extension with the perl |
120 | interpreter. If you install another port of Perl, including the one |
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121 | in the Win32 directory of the Perl distribution, then you'll have to |
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122 | modify the Registry yourself. |
123 | |
124 | =item Macintosh |
125 | |
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126 | Macintosh perl scripts will have the appropriate Creator and |
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127 | Type, so that double-clicking them will invoke the perl application. |
128 | |
129 | =back |
130 | |
131 | Command-interpreters on non-Unix systems have rather different ideas |
132 | on quoting than Unix shells. You'll need to learn the special |
133 | characters in your command-interpreter (C<*>, C<\> and C<"> are |
134 | common) and how to protect whitespace and these characters to run |
135 | one-liners (see C<-e> below). |
136 | |
137 | On some systems, you may have to change single-quotes to double ones, |
138 | which you must I<NOT> do on Unix or Plan9 systems. You might also |
139 | have to change a single % to a %%. |
140 | |
141 | For example: |
142 | |
143 | # Unix |
144 | perl -e 'print "Hello world\n"' |
145 | |
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146 | # MS-DOS, etc. |
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147 | perl -e "print \"Hello world\n\"" |
148 | |
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149 | # Macintosh |
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150 | print "Hello world\n" |
151 | (then Run "Myscript" or Shift-Command-R) |
152 | |
153 | # VMS |
154 | perl -e "print ""Hello world\n""" |
155 | |
156 | The problem is that none of this is reliable: it depends on the command |
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157 | and it is entirely possible neither works. If 4DOS was the command shell, this would |
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158 | probably work better: |
159 | |
160 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
161 | |
162 | CMD.EXE in Windows NT slipped a lot of standard Unix functionality in |
163 | when nobody was looking, but just try to find documentation for its |
164 | quoting rules. |
165 | |
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166 | Under the Macintosh, it depends which environment you are using. The MacPerl |
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167 | shell, or MPW, is much like Unix shells in its support for several |
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168 | quoting variants, except that it makes free use of the Macintosh's non-ASCII |
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169 | characters as control characters. |
170 | |
171 | There is no general solution to all of this. It's just a mess. |
172 | |
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173 | =head2 Switches |
174 | |
175 | A single-character switch may be combined with the following switch, if |
176 | any. |
177 | |
178 | #!/usr/bin/perl -spi.bak # same as -s -p -i.bak |
179 | |
180 | Switches include: |
181 | |
182 | =over 5 |
183 | |
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184 | =item B<-0>[I<digits>] |
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185 | |
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186 | specifies the input record separator (C<$/>) as an octal number. If there are |
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187 | no digits, the null character is the separator. Other switches may |
188 | precede or follow the digits. For example, if you have a version of |
189 | B<find> which can print filenames terminated by the null character, you |
190 | can say this: |
191 | |
192 | find . -name '*.bak' -print0 | perl -n0e unlink |
193 | |
194 | The special value 00 will cause Perl to slurp files in paragraph mode. |
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195 | The value 0777 will cause Perl to slurp files whole because there is no |
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196 | legal character with that value. |
197 | |
198 | =item B<-a> |
199 | |
200 | turns on autosplit mode when used with a B<-n> or B<-p>. An implicit |
201 | split command to the @F array is done as the first thing inside the |
202 | implicit while loop produced by the B<-n> or B<-p>. |
203 | |
204 | perl -ane 'print pop(@F), "\n";' |
205 | |
206 | is equivalent to |
207 | |
208 | while (<>) { |
209 | @F = split(' '); |
210 | print pop(@F), "\n"; |
211 | } |
212 | |
213 | An alternate delimiter may be specified using B<-F>. |
214 | |
215 | =item B<-c> |
216 | |
217 | causes Perl to check the syntax of the script and then exit without |
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218 | executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks, |
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219 | because these are considered as occurring outside the execution of |
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220 | your program. |
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221 | |
222 | =item B<-d> |
223 | |
224 | runs the script under the Perl debugger. See L<perldebug>. |
225 | |
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226 | =item B<-d:>I<foo> |
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227 | |
228 | runs the script under the control of a debugging or tracing module |
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229 | installed as Devel::foo. E.g., B<-d:DProf> executes the script using the |
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230 | Devel::DProf profiler. See L<perldebug>. |
231 | |
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232 | =item B<-D>I<letters> |
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233 | |
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234 | =item B<-D>I<number> |
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235 | |
236 | sets debugging flags. To watch how it executes your script, use |
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237 | B<-Dtls>. (This works only if debugging is compiled into your |
238 | Perl.) Another nice value is B<-Dx>, which lists your compiled |
239 | syntax tree. And B<-Dr> displays compiled regular expressions. As an |
240 | alternative, specify a number instead of list of letters (e.g., B<-D14> is |
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241 | equivalent to B<-Dtls>): |
242 | |
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243 | 1 p Tokenizing and parsing |
244 | 2 s Stack snapshots |
245 | 4 l Context (loop) stack processing |
246 | 8 t Trace execution |
247 | 16 o Method and overloading resolution |
248 | 32 c String/numeric conversions |
249 | 64 P Print preprocessor command for -P |
250 | 128 m Memory allocation |
251 | 256 f Format processing |
252 | 512 r Regular expression parsing and execution |
253 | 1024 x Syntax tree dump |
254 | 2048 u Tainting checks |
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255 | 4096 L Memory leaks (needs C<-DLEAKTEST> when compiling Perl) |
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256 | 8192 H Hash dump -- usurps values() |
257 | 16384 X Scratchpad allocation |
258 | 32768 D Cleaning up |
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259 | |
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260 | All these flags require C<-DDEBUGGING> when you compile the Perl |
261 | executable. This flag is automatically set if you include C<-g> |
262 | option when C<Configure> asks you about optimizer/debugger flags. |
263 | |
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264 | =item B<-e> I<commandline> |
265 | |
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266 | may be used to enter one line of script. |
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267 | If B<-e> is given, Perl |
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268 | will not look for a script filename in the argument list. |
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269 | Multiple B<-e> commands may |
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270 | be given to build up a multi-line script. |
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271 | Make sure to use semicolons where you would in a normal program. |
272 | |
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273 | =item B<-F>I<pattern> |
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274 | |
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275 | specifies the pattern to split on if B<-a> is also in effect. The |
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276 | pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be |
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277 | put in single quotes. |
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278 | |
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279 | =item B<-h> |
280 | |
281 | prints a summary of the options. |
282 | |
283 | =item B<-i>[I<extension>] |
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284 | |
285 | specifies that files processed by the C<E<lt>E<gt>> construct are to be edited |
286 | in-place. It does this by renaming the input file, opening the output |
287 | file by the original name, and selecting that output file as the default |
288 | for print() statements. The extension, if supplied, is added to the name |
289 | of the old file to make a backup copy. If no extension is supplied, no |
290 | backup is made. From the shell, saying |
291 | |
292 | $ perl -p -i.bak -e "s/foo/bar/; ... " |
293 | |
294 | is the same as using the script: |
295 | |
296 | #!/usr/bin/perl -pi.bak |
297 | s/foo/bar/; |
298 | |
299 | which is equivalent to |
300 | |
301 | #!/usr/bin/perl |
302 | while (<>) { |
303 | if ($ARGV ne $oldargv) { |
304 | rename($ARGV, $ARGV . '.bak'); |
305 | open(ARGVOUT, ">$ARGV"); |
306 | select(ARGVOUT); |
307 | $oldargv = $ARGV; |
308 | } |
309 | s/foo/bar/; |
310 | } |
311 | continue { |
312 | print; # this prints to original filename |
313 | } |
314 | select(STDOUT); |
315 | |
316 | except that the B<-i> form doesn't need to compare $ARGV to $oldargv to |
317 | know when the filename has changed. It does, however, use ARGVOUT for |
318 | the selected filehandle. Note that STDOUT is restored as the |
319 | default output filehandle after the loop. |
320 | |
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321 | You can use C<eof> without parenthesis to locate the end of each input file, |
322 | in case you want to append to each file, or reset line numbering (see |
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323 | example in L<perlfunc/eof>). |
324 | |
325 | =item B<-I>I<directory> |
326 | |
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327 | Directories specified by B<-I> are prepended to the search path for |
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328 | modules (C<@INC>), and also tells the C preprocessor where to search for |
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329 | include files. The C preprocessor is invoked with B<-P>; by default it |
330 | searches /usr/include and /usr/lib/perl. |
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331 | |
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332 | =item B<-l>[I<octnum>] |
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333 | |
334 | enables automatic line-ending processing. It has two effects: first, |
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335 | it automatically chomps "C<$/>" (the input record separator) when used |
336 | with B<-n> or B<-p>, and second, it assigns "C<$\>" |
337 | (the output record separator) to have the value of I<octnum> so that |
338 | any print statements will have that separator added back on. If |
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339 | I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For |
340 | instance, to trim lines to 80 columns: |
341 | |
342 | perl -lpe 'substr($_, 80) = ""' |
343 | |
344 | Note that the assignment C<$\ = $/> is done when the switch is processed, |
345 | so the input record separator can be different than the output record |
346 | separator if the B<-l> switch is followed by a B<-0> switch: |
347 | |
348 | gnufind / -print0 | perl -ln0e 'print "found $_" if -p' |
349 | |
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350 | This sets C<$\> to newline and then sets C<$/> to the null character. |
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351 | |
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352 | =item B<-m>[B<->]I<module> |
353 | |
354 | =item B<-M>[B<->]I<module> |
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355 | |
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356 | =item B<-M>[B<->]I<'module ...'> |
357 | |
358 | =item B<-[mM]>[B<->]I<module=arg[,arg]...> |
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359 | |
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360 | C<-m>I<module> executes C<use> I<module> C<();> before executing your |
361 | script. |
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362 | |
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363 | C<-M>I<module> executes C<use> I<module> C<;> before executing your |
364 | script. You can use quotes to add extra code after the module name, |
365 | e.g., C<-M'module qw(foo bar)'>. |
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366 | |
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367 | If the first character after the C<-M> or C<-m> is a dash (C<->) |
368 | then the 'use' is replaced with 'no'. |
369 | |
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370 | A little builtin syntactic sugar means you can also say |
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371 | C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for |
372 | C<-M'module qw(foo bar)'>. This avoids the need to use quotes when |
373 | importing symbols. The actual code generated by C<-Mmodule=foo,bar> is |
374 | C<use module split(/,/,q{foo,bar})>. Note that the C<=> form |
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375 | removes the distinction between C<-m> and C<-M>. |
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376 | |
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377 | =item B<-n> |
378 | |
379 | causes Perl to assume the following loop around your script, which |
380 | makes it iterate over filename arguments somewhat like B<sed -n> or |
381 | B<awk>: |
382 | |
383 | while (<>) { |
384 | ... # your script goes here |
385 | } |
386 | |
387 | Note that the lines are not printed by default. See B<-p> to have |
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388 | lines printed. If a file named by an argument cannot be opened for |
389 | some reason, Perl warns you about it, and moves on to the next file. |
390 | |
391 | Here is an efficient way to delete all files older than a week: |
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392 | |
393 | find . -mtime +7 -print | perl -nle 'unlink;' |
394 | |
395 | This is faster than using the C<-exec> switch of B<find> because you don't |
396 | have to start a process on every filename found. |
397 | |
398 | C<BEGIN> and C<END> blocks may be used to capture control before or after |
399 | the implicit loop, just as in B<awk>. |
400 | |
401 | =item B<-p> |
402 | |
403 | causes Perl to assume the following loop around your script, which |
404 | makes it iterate over filename arguments somewhat like B<sed>: |
405 | |
406 | |
407 | while (<>) { |
408 | ... # your script goes here |
409 | } continue { |
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410 | print or die "-p destination: $!\n"; |
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411 | } |
412 | |
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413 | If a file named by an argument cannot be opened for some reason, Perl |
414 | warns you about it, and moves on to the next file. Note that the |
415 | lines are printed automatically. An error occuring during printing is |
416 | treated as fatal. To suppress printing use the B<-n> switch. A B<-p> |
417 | overrides a B<-n> switch. |
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418 | |
419 | C<BEGIN> and C<END> blocks may be used to capture control before or after |
420 | the implicit loop, just as in awk. |
421 | |
422 | =item B<-P> |
423 | |
424 | causes your script to be run through the C preprocessor before |
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425 | compilation by Perl. (Because both comments and cpp directives begin |
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426 | with the # character, you should avoid starting comments with any words |
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427 | recognized by the C preprocessor such as "if", "else", or "define".) |
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428 | |
429 | =item B<-s> |
430 | |
431 | enables some rudimentary switch parsing for switches on the command |
432 | line after the script name but before any filename arguments (or before |
433 | a B<-->). Any switch found there is removed from @ARGV and sets the |
434 | corresponding variable in the Perl script. The following script |
435 | prints "true" if and only if the script is invoked with a B<-xyz> switch. |
436 | |
437 | #!/usr/bin/perl -s |
438 | if ($xyz) { print "true\n"; } |
439 | |
440 | =item B<-S> |
441 | |
442 | makes Perl use the PATH environment variable to search for the |
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443 | script (unless the name of the script contains directory separators). |
444 | On some platforms, this also makes Perl append suffixes to the |
445 | filename while searching for it. For example, on Win32 platforms, |
446 | the ".bat" and ".cmd" suffixes are appended if a lookup for the |
447 | original name fails, and if the name does not already end in one |
448 | of those suffixes. If your Perl was compiled with DEBUGGING turned |
449 | on, using the -Dp switch to Perl shows how the search progresses. |
450 | |
451 | If the file supplied contains directory separators (i.e. it is an |
452 | absolute or relative pathname), and if the file is not found, |
453 | platforms that append file extensions will do so and try to look |
454 | for the file with those extensions added, one by one. |
455 | |
456 | On DOS-like platforms, if the script does not contain directory |
457 | separators, it will first be searched for in the current directory |
458 | before being searched for on the PATH. On Unix platforms, the |
459 | script will be searched for strictly on the PATH. |
460 | |
461 | Typically this is used to emulate #! startup on platforms that |
462 | don't support #!. This example works on many platforms that |
463 | have a shell compatible with Bourne shell: |
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464 | |
465 | #!/usr/bin/perl |
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466 | eval 'exec /usr/bin/perl -S $0 ${1+"$@"}' |
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467 | if $running_under_some_shell; |
468 | |
469 | The system ignores the first line and feeds the script to /bin/sh, |
470 | which proceeds to try to execute the Perl script as a shell script. |
471 | The shell executes the second line as a normal shell command, and thus |
472 | starts up the Perl interpreter. On some systems $0 doesn't always |
473 | contain the full pathname, so the B<-S> tells Perl to search for the |
474 | script if necessary. After Perl locates the script, it parses the |
475 | lines and ignores them because the variable $running_under_some_shell |
476 | is never true. A better construct than C<$*> would be C<${1+"$@"}>, which |
477 | handles embedded spaces and such in the filenames, but doesn't work if |
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478 | the script is being interpreted by csh. To start up sh rather |
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479 | than csh, some systems may have to replace the #! line with a line |
480 | containing just a colon, which will be politely ignored by Perl. Other |
481 | systems can't control that, and need a totally devious construct that |
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482 | will work under any of csh, sh, or Perl, such as the following: |
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483 | |
484 | eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}' |
485 | & eval 'exec /usr/bin/perl -S $0 $argv:q' |
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486 | if $running_under_some_shell; |
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487 | |
488 | =item B<-T> |
489 | |
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490 | forces "taint" checks to be turned on so you can test them. Ordinarily these checks are |
491 | done only when running setuid or setgid. It's a good idea to turn |
492 | them on explicitly for programs run on another's behalf, such as CGI |
493 | programs. See L<perlsec>. |
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494 | |
495 | =item B<-u> |
496 | |
497 | causes Perl to dump core after compiling your script. You can then |
498 | take this core dump and turn it into an executable file by using the |
499 | B<undump> program (not supplied). This speeds startup at the expense of |
500 | some disk space (which you can minimize by stripping the executable). |
501 | (Still, a "hello world" executable comes out to about 200K on my |
502 | machine.) If you want to execute a portion of your script before dumping, |
503 | use the dump() operator instead. Note: availability of B<undump> is |
504 | platform specific and may not be available for a specific port of |
505 | Perl. |
506 | |
507 | =item B<-U> |
508 | |
509 | allows Perl to do unsafe operations. Currently the only "unsafe" |
510 | operations are the unlinking of directories while running as superuser, |
511 | and running setuid programs with fatal taint checks turned into |
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512 | warnings. Note that the B<-w> switch (or the C<$^W> variable) must |
513 | be used along with this option to actually B<generate> the |
514 | taint-check warnings. |
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515 | |
516 | =item B<-v> |
517 | |
518 | prints the version and patchlevel of your Perl executable. |
519 | |
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520 | =item B<-V> |
521 | |
522 | prints summary of the major perl configuration values and the current |
523 | value of @INC. |
524 | |
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525 | =item B<-V:>I<name> |
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526 | |
527 | Prints to STDOUT the value of the named configuration variable. |
528 | |
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529 | =item B<-w> |
530 | |
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531 | prints warnings about variable names that are mentioned only once, and |
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532 | scalar variables that are used before being set. Also warns about |
533 | redefined subroutines, and references to undefined filehandles or |
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534 | filehandles opened read-only that you are attempting to write on. Also |
774d564b |
535 | warns you if you use values as a number that doesn't look like numbers, |
536 | using an array as though it were a scalar, if your subroutines recurse |
537 | more than 100 deep, and innumerable other things. |
538 | |
539 | You can disable specific warnings using C<__WARN__> hooks, as described |
540 | in L<perlvar> and L<perlfunc/warn>. See also L<perldiag> and L<perltrap>. |
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541 | |
542 | =item B<-x> I<directory> |
543 | |
544 | tells Perl that the script is embedded in a message. Leading |
545 | garbage will be discarded until the first line that starts with #! and |
546 | contains the string "perl". Any meaningful switches on that line will |
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547 | be applied. If a directory name is specified, Perl will switch to |
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548 | that directory before running the script. The B<-x> switch controls |
549 | only the disposal of leading garbage. The script must be |
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550 | terminated with C<__END__> if there is trailing garbage to be ignored (the |
551 | script can process any or all of the trailing garbage via the DATA |
552 | filehandle if desired). |
553 | |
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554 | =back |
555 | |
556 | =head1 ENVIRONMENT |
557 | |
558 | =over 12 |
559 | |
560 | =item HOME |
561 | |
562 | Used if chdir has no argument. |
563 | |
564 | =item LOGDIR |
565 | |
566 | Used if chdir has no argument and HOME is not set. |
567 | |
568 | =item PATH |
569 | |
570 | Used in executing subprocesses, and in finding the script if B<-S> is |
571 | used. |
572 | |
573 | =item PERL5LIB |
574 | |
575 | A colon-separated list of directories in which to look for Perl library |
576 | files before looking in the standard library and the current |
577 | directory. If PERL5LIB is not defined, PERLLIB is used. When running |
578 | taint checks (because the script was running setuid or setgid, or the |
579 | B<-T> switch was used), neither variable is used. The script should |
580 | instead say |
581 | |
582 | use lib "/my/directory"; |
583 | |
54310121 |
584 | =item PERL5OPT |
585 | |
586 | Command-line options (switches). Switches in this variable are taken |
587 | as if they were on every Perl command line. Only the B<-[DIMUdmw]> |
588 | switches are allowed. When running taint checks (because the script |
589 | was running setuid or setgid, or the B<-T> switch was used), this |
590 | variable is ignored. |
591 | |
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592 | =item PERLLIB |
593 | |
594 | A colon-separated list of directories in which to look for Perl library |
595 | files before looking in the standard library and the current directory. |
596 | If PERL5LIB is defined, PERLLIB is not used. |
597 | |
598 | =item PERL5DB |
599 | |
600 | The command used to load the debugger code. The default is: |
601 | |
602 | BEGIN { require 'perl5db.pl' } |
603 | |
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604 | =item PERL5SHELL (specific to WIN32 port) |
605 | |
606 | May be set to an alternative shell that perl must use internally for |
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607 | executing "backtick" commands or system(). Default is C<cmd.exe /x/c> |
608 | on WindowsNT and C<command.com /c> on Windows95. The value is considered |
609 | to be space delimited. Precede any character that needs to be protected |
610 | (like a space or backslash) with a backslash. |
611 | |
612 | Note that Perl doesn't use COMSPEC for this purpose because |
613 | COMSPEC has a high degree of variability among users, leading to |
614 | portability concerns. Besides, perl can use a shell that may not be |
615 | fit for interactive use, and setting COMSPEC to such a shell may |
616 | interfere with the proper functioning of other programs (which usually |
617 | look in COMSPEC to find a shell fit for interactive use). |
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618 | |
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619 | =item PERL_DEBUG_MSTATS |
620 | |
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621 | Relevant only if perl is compiled with the malloc included with the perl |
622 | distribution (that is, if C<perl -V:d_mymalloc> is 'define'), |
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623 | if set, this causes memory statistics to be dumped after execution. If set |
624 | to an integer greater than one, also causes memory statistics to be dumped |
625 | after compilation. |
626 | |
627 | =item PERL_DESTRUCT_LEVEL |
628 | |
629 | Relevant only if your perl executable was built with B<-DDEBUGGING>, |
630 | this controls the behavior of global destruction of objects and other |
631 | references. |
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632 | |
633 | =back |
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634 | |
635 | Perl also has environment variables that control how Perl handles data |
636 | specific to particular natural languages. See L<perllocale>. |
637 | |
638 | Apart from these, Perl uses no other environment variables, except |
639 | to make them available to the script being executed, and to child |
640 | processes. However, scripts running setuid would do well to execute |
641 | the following lines before doing anything else, just to keep people |
642 | honest: |
643 | |
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644 | $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need |
645 | $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL}; |
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646 | delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; |
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647 | |