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1 | =head1 NAME |
2 | |
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3 | perlfaq3 - Programming Tools ($Revision: 1.33 $, $Date: 1998/12/29 20:12:12 $) |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This section of the FAQ answers questions related to programmer tools |
8 | and programming support. |
9 | |
10 | =head2 How do I do (anything)? |
11 | |
12 | Have you looked at CPAN (see L<perlfaq2>)? The chances are that |
13 | someone has already written a module that can solve your problem. |
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14 | Have you read the appropriate man pages? Here's a brief index: |
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15 | |
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16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
17 | Execution perlrun, perldebug |
18 | Functions perlfunc |
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19 | Objects perlref, perlmod, perlobj, perltie |
20 | Data Structures perlref, perllol, perldsc |
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21 | Modules perlmod, perlmodlib, perlsub |
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22 | Regexps perlre, perlfunc, perlop, perllocale |
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23 | Moving to perl5 perltrap, perl |
24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed |
25 | Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html |
26 | (not a man-page but still useful) |
27 | |
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28 | L<perltoc> provides a crude table of contents for the perl man page set. |
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29 | |
30 | =head2 How can I use Perl interactively? |
31 | |
32 | The typical approach uses the Perl debugger, described in the |
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33 | perldebug(1) man page, on an ``empty'' program, like this: |
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34 | |
35 | perl -de 42 |
36 | |
37 | Now just type in any legal Perl code, and it will be immediately |
38 | evaluated. You can also examine the symbol table, get stack |
39 | backtraces, check variable values, set breakpoints, and other |
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40 | operations typically found in symbolic debuggers. |
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41 | |
42 | =head2 Is there a Perl shell? |
43 | |
44 | In general, no. The Shell.pm module (distributed with perl) makes |
45 | perl try commands which aren't part of the Perl language as shell |
46 | commands. perlsh from the source distribution is simplistic and |
47 | uninteresting, but may still be what you want. |
48 | |
49 | =head2 How do I debug my Perl programs? |
50 | |
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51 | Have you used C<-w>? It enables warnings for dubious practices. |
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52 | |
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53 | Have you tried C<use strict>? It prevents you from using symbolic |
54 | references, makes you predeclare any subroutines that you call as bare |
55 | words, and (probably most importantly) forces you to predeclare your |
56 | variables with C<my> or C<use vars>. |
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57 | |
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58 | Did you check the returns of each and every system call? The operating |
59 | system (and thus Perl) tells you whether they worked or not, and if not |
60 | why. |
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61 | |
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62 | open(FH, "> /etc/cantwrite") |
63 | or die "Couldn't write to /etc/cantwrite: $!\n"; |
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64 | |
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65 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
66 | programmers, and even has sections for those of you who are upgrading |
67 | from languages like I<awk> and I<C>. |
68 | |
69 | Have you tried the Perl debugger, described in L<perldebug>? You can |
70 | step through your program and see what it's doing and thus work out |
71 | why what it's doing isn't what it should be doing. |
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72 | |
73 | =head2 How do I profile my Perl programs? |
74 | |
75 | You should get the Devel::DProf module from CPAN, and also use |
76 | Benchmark.pm from the standard distribution. Benchmark lets you time |
77 | specific portions of your code, while Devel::DProf gives detailed |
78 | breakdowns of where your code spends its time. |
79 | |
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80 | Here's a sample use of Benchmark: |
81 | |
82 | use Benchmark; |
83 | |
84 | @junk = `cat /etc/motd`; |
85 | $count = 10_000; |
86 | |
87 | timethese($count, { |
88 | 'map' => sub { my @a = @junk; |
89 | map { s/a/b/ } @a; |
90 | return @a |
91 | }, |
92 | 'for' => sub { my @a = @junk; |
93 | local $_; |
94 | for (@a) { s/a/b/ }; |
95 | return @a }, |
96 | }); |
97 | |
98 | This is what it prints (on one machine--your results will be dependent |
99 | on your hardware, operating system, and the load on your machine): |
100 | |
101 | Benchmark: timing 10000 iterations of for, map... |
102 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
103 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
104 | |
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105 | Be aware that a good benchmark is very hard to write. It only tests the |
106 | data you give it, and really proves little about differing complexities |
107 | of contrasting algorithms. |
108 | |
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109 | =head2 How do I cross-reference my Perl programs? |
110 | |
111 | The B::Xref module, shipped with the new, alpha-release Perl compiler |
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112 | (not the general distribution prior to the 5.005 release), can be used |
113 | to generate cross-reference reports for Perl programs. |
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114 | |
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115 | perl -MO=Xref[,OPTIONS] scriptname.plx |
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116 | |
117 | =head2 Is there a pretty-printer (formatter) for Perl? |
118 | |
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119 | There is no program that will reformat Perl as much as indent(1) does |
120 | for C. The complex feedback between the scanner and the parser (this |
121 | feedback is what confuses the vgrind and emacs programs) makes it |
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122 | challenging at best to write a stand-alone Perl parser. |
123 | |
124 | Of course, if you simply follow the guidelines in L<perlstyle>, you |
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125 | shouldn't need to reformat. The habit of formatting your code as you |
126 | write it will help prevent bugs. Your editor can and should help you |
127 | with this. The perl-mode for emacs can provide a remarkable amount of |
128 | help with most (but not all) code, and even less programmable editors |
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129 | can provide significant assistance. Tom swears by the following |
130 | settings in vi and its clones: |
131 | |
132 | set ai sw=4 |
133 | map ^O {^M}^[O^T |
134 | |
135 | Now put that in your F<.exrc> file (replacing the caret characters |
136 | with control characters) and away you go. In insert mode, ^T is |
137 | for indenting, ^D is for undenting, and ^O is for blockdenting -- |
138 | as it were. If you haven't used the last one, you're missing |
139 | a lot. A more complete example, with comments, can be found at |
140 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz |
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141 | |
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142 | If you are used to using the I<vgrind> program for printing out nice code |
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143 | to a laser printer, you can take a stab at this using |
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144 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
145 | results are not particularly satisfying for sophisticated code. |
146 | |
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147 | The a2ps at http://www.infres.enst.fr/~demaille/a2ps/ does lots of things |
148 | related to generating nicely printed output of documents. |
149 | |
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150 | =head2 Is there a ctags for Perl? |
151 | |
152 | There's a simple one at |
153 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
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154 | the trick. And if not, it's easy to hack into what you want. |
155 | |
156 | =head2 Is there an IDE or Windows Perl Editor? |
157 | |
158 | If you're on Unix, you already have an IDE -- Unix itself. |
159 | You just have to learn the toolbox. If you're not, then you |
160 | probably don't have a toolbox, so may need something else. |
161 | |
162 | PerlBuilder (XXX URL to follow) is an integrated development |
163 | environment for Windows that supports Perl development. Perl programs |
164 | are just plain text, though, so you could download emacs for Windows |
165 | (XXX) or vim for win32 (http://www.cs.vu.nl/~tmgil/vi.html). If |
166 | you're transferring Windows files to Unix, be sure to transfer in |
167 | ASCII mode so the ends of lines are appropriately converted. |
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168 | |
169 | =head2 Where can I get Perl macros for vi? |
170 | |
171 | For a complete version of Tom Christiansen's vi configuration file, |
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172 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz, |
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173 | the standard benchmark file for vi emulators. This runs best with nvi, |
174 | the current version of vi out of Berkeley, which incidentally can be built |
175 | with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc. |
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176 | |
177 | =head2 Where can I get perl-mode for emacs? |
178 | |
179 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
180 | perl-mode.el and support for the perl debugger built in. These should |
181 | come with the standard Emacs 19 distribution. |
182 | |
183 | In the perl source directory, you'll find a directory called "emacs", |
184 | which contains a cperl-mode that color-codes keywords, provides |
185 | context-sensitive help, and other nifty things. |
186 | |
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187 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
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188 | (single quote), and mess up the indentation and hilighting. You |
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189 | are probably using C<"main::foo"> in new Perl code anyway, so this |
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190 | shouldn't be an issue. |
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191 | |
192 | =head2 How can I use curses with Perl? |
193 | |
194 | The Curses module from CPAN provides a dynamically loadable object |
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195 | module interface to a curses library. A small demo can be found at the |
196 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; |
197 | this program repeats a command and updates the screen as needed, rendering |
198 | B<rep ps axu> similar to B<top>. |
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199 | |
200 | =head2 How can I use X or Tk with Perl? |
201 | |
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202 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
203 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
204 | to the Athena Widget set. Both are available from CPAN. See the |
205 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ |
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206 | |
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207 | Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at |
208 | http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
209 | Guide available at |
210 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the |
211 | online manpages at |
212 | http://www-users.cs.umn.edu/~amundson/perl/perltk/toc.html . |
213 | |
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214 | =head2 How can I generate simple menus without using CGI or Tk? |
215 | |
216 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz |
217 | module, which is curses-based, can help with this. |
218 | |
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219 | =head2 What is undump? |
220 | |
221 | See the next questions. |
222 | |
223 | =head2 How can I make my Perl program run faster? |
224 | |
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225 | The best way to do this is to come up with a better algorithm. This |
226 | can often make a dramatic difference. Chapter 8 in the Camel has some |
227 | efficiency tips in it you might want to look at. Jon Bentley's book |
228 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
229 | on optimization, too. Advice on benchmarking boils down to: benchmark |
230 | and profile to make sure you're optimizing the right part, look for |
231 | better algorithms instead of microtuning your code, and when all else |
232 | fails consider just buying faster hardware. |
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233 | |
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234 | A different approach is to autoload seldom-used Perl code. See the |
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235 | AutoSplit and AutoLoader modules in the standard distribution for |
236 | that. Or you could locate the bottleneck and think about writing just |
237 | that part in C, the way we used to take bottlenecks in C code and |
238 | write them in assembler. Similar to rewriting in C is the use of |
239 | modules that have critical sections written in C (for instance, the |
240 | PDL module from CPAN). |
241 | |
242 | In some cases, it may be worth it to use the backend compiler to |
243 | produce byte code (saving compilation time) or compile into C, which |
244 | will certainly save compilation time and sometimes a small amount (but |
245 | not much) execution time. See the question about compiling your Perl |
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246 | programs for more on the compiler--the wins aren't as obvious as you'd |
247 | hope. |
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248 | |
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249 | If you're currently linking your perl executable to a shared I<libc.so>, |
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250 | you can often gain a 10-25% performance benefit by rebuilding it to |
251 | link with a static libc.a instead. This will make a bigger perl |
252 | executable, but your Perl programs (and programmers) may thank you for |
253 | it. See the F<INSTALL> file in the source distribution for more |
254 | information. |
255 | |
256 | Unsubstantiated reports allege that Perl interpreters that use sfio |
257 | outperform those that don't (for IO intensive applications). To try |
258 | this, see the F<INSTALL> file in the source distribution, especially |
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259 | the ``Selecting File IO mechanisms'' section. |
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260 | |
261 | The undump program was an old attempt to speed up your Perl program |
262 | by storing the already-compiled form to disk. This is no longer |
263 | a viable option, as it only worked on a few architectures, and |
264 | wasn't a good solution anyway. |
265 | |
266 | =head2 How can I make my Perl program take less memory? |
267 | |
268 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
269 | throw memory at a problem. Scalars in Perl use more memory than |
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270 | strings in C, arrays take more than that, and hashes use even more. While |
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271 | there's still a lot to be done, recent releases have been addressing |
272 | these issues. For example, as of 5.004, duplicate hash keys are |
273 | shared amongst all hashes using them, so require no reallocation. |
274 | |
275 | In some cases, using substr() or vec() to simulate arrays can be |
276 | highly beneficial. For example, an array of a thousand booleans will |
277 | take at least 20,000 bytes of space, but it can be turned into one |
278 | 125-byte bit vector for a considerable memory savings. The standard |
279 | Tie::SubstrHash module can also help for certain types of data |
280 | structure. If you're working with specialist data structures |
281 | (matrices, for instance) modules that implement these in C may use |
282 | less memory than equivalent Perl modules. |
283 | |
284 | Another thing to try is learning whether your Perl was compiled with |
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285 | the system malloc or with Perl's builtin malloc. Whichever one it |
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286 | is, try using the other one and see whether this makes a difference. |
287 | Information about malloc is in the F<INSTALL> file in the source |
288 | distribution. You can find out whether you are using perl's malloc by |
289 | typing C<perl -V:usemymalloc>. |
290 | |
291 | =head2 Is it unsafe to return a pointer to local data? |
292 | |
293 | No, Perl's garbage collection system takes care of this. |
294 | |
295 | sub makeone { |
296 | my @a = ( 1 .. 10 ); |
297 | return \@a; |
298 | } |
299 | |
300 | for $i ( 1 .. 10 ) { |
301 | push @many, makeone(); |
302 | } |
303 | |
304 | print $many[4][5], "\n"; |
305 | |
306 | print "@many\n"; |
307 | |
308 | =head2 How can I free an array or hash so my program shrinks? |
309 | |
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310 | You can't. On most operating systems, memory allocated to a program |
311 | can never be returned to the system. That's why long-running programs |
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312 | sometimes re-exec themselves. Some operating systems (notably, |
313 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no |
314 | longer used, but it doesn't appear to happen with Perl (yet). The Mac |
315 | appears to be the only platform that will reliably (albeit, slowly) |
316 | return memory to the OS. |
317 | |
318 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef |
319 | $scalar> will return memory to the system, while on Solaris 2.6 it |
320 | won't. In general, try it yourself and see. |
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321 | |
322 | However, judicious use of my() on your variables will help make sure |
323 | that they go out of scope so that Perl can free up their storage for |
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324 | use in other parts of your program. A global variable, of course, never |
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325 | goes out of scope, so you can't get its space automatically reclaimed, |
326 | although undef()ing and/or delete()ing it will achieve the same effect. |
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327 | In general, memory allocation and de-allocation isn't something you can |
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328 | or should be worrying about much in Perl, but even this capability |
329 | (preallocation of data types) is in the works. |
330 | |
331 | =head2 How can I make my CGI script more efficient? |
332 | |
333 | Beyond the normal measures described to make general Perl programs |
334 | faster or smaller, a CGI program has additional issues. It may be run |
335 | several times per second. Given that each time it runs it will need |
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336 | to be re-compiled and will often allocate a megabyte or more of system |
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337 | memory, this can be a killer. Compiling into C B<isn't going to help |
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338 | you> because the process start-up overhead is where the bottleneck is. |
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339 | |
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340 | There are two popular ways to avoid this overhead. One solution |
341 | involves running the Apache HTTP server (available from |
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342 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
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343 | plugin modules. |
344 | |
345 | With mod_perl and the Apache::Registry module (distributed with |
346 | mod_perl), httpd will run with an embedded Perl interpreter which |
347 | pre-compiles your script and then executes it within the same address |
348 | space without forking. The Apache extension also gives Perl access to |
349 | the internal server API, so modules written in Perl can do just about |
350 | anything a module written in C can. For more on mod_perl, see |
351 | http://perl.apache.org/ |
352 | |
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353 | With the FCGI module (from CPAN) and the mod_fastcgi |
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354 | module (available from http://www.fastcgi.com/) each of your perl |
355 | scripts becomes a permanent CGI daemon process. |
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356 | |
357 | Both of these solutions can have far-reaching effects on your system |
358 | and on the way you write your CGI scripts, so investigate them with |
359 | care. |
360 | |
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361 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
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362 | |
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363 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
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364 | (http://www.binevolve.com/ or http://www.binevolve.com/bine/vep) might |
365 | also be worth looking at. It will allow you to increase the performance |
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366 | of your perl scripts, upto 25 times faster than normal CGI perl by |
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367 | running in persistent perl mode, or 4 to 5 times faster without any |
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368 | modification to your existing CGI scripts. Fully functional evaluation |
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369 | copies are available from the web site. |
370 | |
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371 | =head2 How can I hide the source for my Perl program? |
372 | |
373 | Delete it. :-) Seriously, there are a number of (mostly |
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374 | unsatisfactory) solutions with varying levels of ``security''. |
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375 | |
376 | First of all, however, you I<can't> take away read permission, because |
377 | the source code has to be readable in order to be compiled and |
378 | interpreted. (That doesn't mean that a CGI script's source is |
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379 | readable by people on the web, though, only by people with access to |
380 | the filesystem) So you have to leave the permissions at the socially |
381 | friendly 0755 level. |
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382 | |
383 | Some people regard this as a security problem. If your program does |
384 | insecure things, and relies on people not knowing how to exploit those |
385 | insecurities, it is not secure. It is often possible for someone to |
386 | determine the insecure things and exploit them without viewing the |
387 | source. Security through obscurity, the name for hiding your bugs |
388 | instead of fixing them, is little security indeed. |
389 | |
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390 | You can try using encryption via source filters (Filter::* from CPAN), |
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391 | but any decent programmer will be able to decrypt it. You can try using |
392 | the byte code compiler and interpreter described below, but the curious |
393 | might still be able to de-compile it. You can try using the native-code |
394 | compiler described below, but crackers might be able to disassemble it. |
395 | These pose varying degrees of difficulty to people wanting to get at |
396 | your code, but none can definitively conceal it (this is true of every |
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397 | language, not just Perl). |
398 | |
399 | If you're concerned about people profiting from your code, then the |
400 | bottom line is that nothing but a restrictive licence will give you |
401 | legal security. License your software and pepper it with threatening |
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402 | statements like ``This is unpublished proprietary software of XYZ Corp. |
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403 | Your access to it does not give you permission to use it blah blah |
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404 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
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405 | you want to be sure your licence's wording will stand up in court. |
406 | |
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407 | =head2 How can I compile my Perl program into byte code or C? |
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408 | |
409 | Malcolm Beattie has written a multifunction backend compiler, |
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410 | available from CPAN, that can do both these things. It is included |
411 | in the perl5.005 release, but is still considered experimental. |
412 | This means it's fun to play with if you're a programmer but not |
413 | really for people looking for turn-key solutions. |
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414 | |
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415 | Merely compiling into C does not in and of itself guarantee that your |
416 | code will run very much faster. That's because except for lucky cases |
417 | where a lot of native type inferencing is possible, the normal Perl |
418 | run time system is still present and so your program will take just as |
419 | long to run and be just as big. Most programs save little more than |
420 | compilation time, leaving execution no more than 10-30% faster. A few |
421 | rare programs actually benefit significantly (like several times |
422 | faster), but this takes some tweaking of your code. |
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423 | |
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424 | You'll probably be astonished to learn that the current version of the |
425 | compiler generates a compiled form of your script whose executable is |
426 | just as big as the original perl executable, and then some. That's |
427 | because as currently written, all programs are prepared for a full |
428 | eval() statement. You can tremendously reduce this cost by building a |
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429 | shared I<libperl.so> library and linking against that. See the |
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430 | F<INSTALL> podfile in the perl source distribution for details. If |
431 | you link your main perl binary with this, it will make it miniscule. |
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432 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
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433 | size! |
434 | |
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435 | In general, the compiler will do nothing to make a Perl program smaller, |
436 | faster, more portable, or more secure. In fact, it will usually hurt |
437 | all of those. The executable will be bigger, your VM system may take |
438 | longer to load the whole thing, the binary is fragile and hard to fix, |
439 | and compilation never stopped software piracy in the form of crackers, |
440 | viruses, or bootleggers. The real advantage of the compiler is merely |
441 | packaging, and once you see the size of what it makes (well, unless |
442 | you use a shared I<libperl.so>), you'll probably want a complete |
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443 | Perl install anyway. |
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444 | |
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445 | =head2 How can I compile Perl into Java? |
446 | |
447 | You can't. Not yet, anyway. You can integrate Java and Perl with the |
448 | Perl Resource Kit from O'Reilly and Associates. See |
449 | http://www.oreilly.com/catalog/prkunix/ for more information. |
450 | The Java interface will be supported in the core 5.006 release |
451 | of Perl. |
452 | |
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453 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
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454 | |
455 | For OS/2 just use |
456 | |
457 | extproc perl -S -your_switches |
458 | |
459 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
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460 | `extproc' handling). For DOS one should first invent a corresponding |
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461 | batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the |
462 | F<INSTALL> file in the source distribution for more information). |
463 | |
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464 | The Win95/NT installation, when using the ActiveState port of Perl, |
465 | will modify the Registry to associate the C<.pl> extension with the |
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466 | perl interpreter. If you install another port (Gurusamy Sarathy's is |
467 | the recommended Win95/NT port), or (eventually) build your own |
468 | Win95/NT Perl using a Windows port of gcc (e.g., with cygwin32 or |
469 | mingw32), then you'll have to modify the Registry yourself. In |
470 | addition to associating C<.pl> with the interpreter, NT people can |
471 | use: C<SET PATHEXT=%PATHEXT%;.PL> to let them run the program |
472 | C<install-linux.pl> merely by typing C<install-linux>. |
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473 | |
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474 | Macintosh perl scripts will have the appropriate Creator and |
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475 | Type, so that double-clicking them will invoke the perl application. |
476 | |
477 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
478 | throw the perl interpreter into your cgi-bin directory, in order to |
479 | get your scripts working for a web server. This is an EXTREMELY big |
480 | security risk. Take the time to figure out how to do it correctly. |
481 | |
482 | =head2 Can I write useful perl programs on the command line? |
483 | |
484 | Yes. Read L<perlrun> for more information. Some examples follow. |
485 | (These assume standard Unix shell quoting rules.) |
486 | |
487 | # sum first and last fields |
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488 | perl -lane 'print $F[0] + $F[-1]' * |
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489 | |
490 | # identify text files |
491 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
492 | |
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493 | # remove (most) comments from C program |
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494 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
495 | |
496 | # make file a month younger than today, defeating reaper daemons |
497 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
498 | |
499 | # find first unused uid |
500 | perl -le '$i++ while getpwuid($i); print $i' |
501 | |
502 | # display reasonable manpath |
503 | echo $PATH | perl -nl -072 -e ' |
504 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
505 | |
506 | Ok, the last one was actually an obfuscated perl entry. :-) |
507 | |
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508 | =head2 Why don't perl one-liners work on my DOS/Mac/VMS system? |
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509 | |
510 | The problem is usually that the command interpreters on those systems |
511 | have rather different ideas about quoting than the Unix shells under |
512 | which the one-liners were created. On some systems, you may have to |
513 | change single-quotes to double ones, which you must I<NOT> do on Unix |
514 | or Plan9 systems. You might also have to change a single % to a %%. |
515 | |
516 | For example: |
517 | |
518 | # Unix |
519 | perl -e 'print "Hello world\n"' |
520 | |
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521 | # DOS, etc. |
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522 | perl -e "print \"Hello world\n\"" |
523 | |
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524 | # Mac |
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525 | print "Hello world\n" |
526 | (then Run "Myscript" or Shift-Command-R) |
527 | |
528 | # VMS |
529 | perl -e "print ""Hello world\n""" |
530 | |
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531 | The problem is that none of this is reliable: it depends on the |
532 | command interpreter. Under Unix, the first two often work. Under DOS, |
533 | it's entirely possible neither works. If 4DOS was the command shell, |
534 | you'd probably have better luck like this: |
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535 | |
536 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
537 | |
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538 | Under the Mac, it depends which environment you are using. The MacPerl |
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539 | shell, or MPW, is much like Unix shells in its support for several |
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540 | quoting variants, except that it makes free use of the Mac's non-ASCII |
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541 | characters as control characters. |
542 | |
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543 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
544 | quotes', and `backticks`, may make one-liners easier to write. |
545 | |
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546 | There is no general solution to all of this. It is a mess, pure and |
547 | simple. Sucks to be away from Unix, huh? :-) |
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548 | |
549 | [Some of this answer was contributed by Kenneth Albanowski.] |
550 | |
551 | =head2 Where can I learn about CGI or Web programming in Perl? |
552 | |
553 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
554 | see the two especially dedicated to web stuff in the question on |
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555 | books. For problems and questions related to the web, like ``Why |
556 | do I get 500 Errors'' or ``Why doesn't it run from the browser right |
557 | when it runs fine on the command line'', see these sources: |
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558 | |
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559 | WWW Security FAQ |
560 | http://www.w3.org/Security/Faq/ |
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561 | |
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562 | Web FAQ |
563 | http://www.boutell.com/faq/ |
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564 | |
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565 | CGI FAQ |
566 | http://www.webthing.com/page.cgi/cgifaq |
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567 | |
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568 | HTTP Spec |
569 | http://www.w3.org/pub/WWW/Protocols/HTTP/ |
570 | |
571 | HTML Spec |
572 | http://www.w3.org/TR/REC-html40/ |
573 | http://www.w3.org/pub/WWW/MarkUp/ |
574 | |
575 | CGI Spec |
576 | http://www.w3.org/CGI/ |
577 | |
578 | CGI Security FAQ |
579 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt |
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580 | |
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581 | |
582 | =head2 Where can I learn about object-oriented Perl programming? |
583 | |
584 | L<perltoot> is a good place to start, and you can use L<perlobj> and |
585 | L<perlbot> for reference. Perltoot didn't come out until the 5.004 |
586 | release, but you can get a copy (in pod, html, or postscript) from |
587 | http://www.perl.com/CPAN/doc/FMTEYEWTK/ . |
588 | |
589 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] |
590 | |
591 | If you want to call C from Perl, start with L<perlxstut>, |
592 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
593 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
594 | L<perlguts>. Don't forget that you can learn a lot from looking at |
595 | how the authors of existing extension modules wrote their code and |
596 | solved their problems. |
597 | |
598 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in |
599 | my C program, what am I doing wrong? |
600 | |
601 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
602 | the tests pass, read the pods again and again and again. If they |
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603 | fail, see L<perlbug> and send a bugreport with the output of |
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604 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
605 | |
606 | =head2 When I tried to run my script, I got this message. What does it |
607 | mean? |
608 | |
609 | L<perldiag> has a complete list of perl's error messages and warnings, |
610 | with explanatory text. You can also use the splain program (distributed |
611 | with perl) to explain the error messages: |
612 | |
613 | perl program 2>diag.out |
614 | splain [-v] [-p] diag.out |
615 | |
616 | or change your program to explain the messages for you: |
617 | |
618 | use diagnostics; |
619 | |
620 | or |
621 | |
622 | use diagnostics -verbose; |
623 | |
624 | =head2 What's MakeMaker? |
625 | |
626 | This module (part of the standard perl distribution) is designed to |
627 | write a Makefile for an extension module from a Makefile.PL. For more |
628 | information, see L<ExtUtils::MakeMaker>. |
629 | |
630 | =head1 AUTHOR AND COPYRIGHT |
631 | |
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632 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
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633 | All rights reserved. |
634 | |
c8db1d39 |
635 | When included as an integrated part of the Standard Distribution |
636 | of Perl or of its documentation (printed or otherwise), this works is |
637 | covered under Perl's Artistic Licence. For separate distributions of |
638 | all or part of this FAQ outside of that, see L<perlfaq>. |
639 | |
640 | Irrespective of its distribution, all code examples here are public |
641 | domain. You are permitted and encouraged to use this code and any |
642 | derivatives thereof in your own programs for fun or for profit as you |
643 | see fit. A simple comment in the code giving credit to the FAQ would |
644 | be courteous but is not required. |
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645 | |