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68dc0745 | 1 | =head1 NAME |
2 | ||
d92eb7b0 | 3 | perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $) |
68dc0745 | 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. | |
46fc3d4c | 14 | Have you read the appropriate man pages? Here's a brief index: |
68dc0745 | 15 | |
5a964f20 TC |
16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
17 | Execution perlrun, perldebug | |
18 | Functions perlfunc | |
68dc0745 | 19 | Objects perlref, perlmod, perlobj, perltie |
20 | Data Structures perlref, perllol, perldsc | |
f102b883 | 21 | Modules perlmod, perlmodlib, perlsub |
d92eb7b0 | 22 | Regexes perlre, perlfunc, perlop, perllocale |
68dc0745 | 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 | ||
87275199 | 28 | A crude table of contents for the Perl man page set is found in L<perltoc>. |
68dc0745 | 29 | |
30 | =head2 How can I use Perl interactively? | |
31 | ||
32 | The typical approach uses the Perl debugger, described in the | |
92c2ed05 | 33 | perldebug(1) man page, on an ``empty'' program, like this: |
68dc0745 | 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 | |
92c2ed05 | 40 | operations typically found in symbolic debuggers. |
68dc0745 | 41 | |
42 | =head2 Is there a Perl shell? | |
43 | ||
87275199 GS |
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 | |
68dc0745 | 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 | ||
9f1b1f2d GS |
51 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
52 | for dubious practices. | |
68dc0745 | 53 | |
92c2ed05 GS |
54 | Have you tried C<use strict>? It prevents you from using symbolic |
55 | references, makes you predeclare any subroutines that you call as bare | |
56 | words, and (probably most importantly) forces you to predeclare your | |
77ca0c92 | 57 | variables with C<my> or C<our> or C<use vars>. |
68dc0745 | 58 | |
92c2ed05 GS |
59 | Did you check the returns of each and every system call? The operating |
60 | system (and thus Perl) tells you whether they worked or not, and if not | |
61 | why. | |
68dc0745 | 62 | |
92c2ed05 GS |
63 | open(FH, "> /etc/cantwrite") |
64 | or die "Couldn't write to /etc/cantwrite: $!\n"; | |
68dc0745 | 65 | |
92c2ed05 GS |
66 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
67 | programmers, and even has sections for those of you who are upgrading | |
68 | from languages like I<awk> and I<C>. | |
69 | ||
70 | Have you tried the Perl debugger, described in L<perldebug>? You can | |
71 | step through your program and see what it's doing and thus work out | |
72 | why what it's doing isn't what it should be doing. | |
68dc0745 | 73 | |
74 | =head2 How do I profile my Perl programs? | |
75 | ||
76 | You should get the Devel::DProf module from CPAN, and also use | |
77 | Benchmark.pm from the standard distribution. Benchmark lets you time | |
78 | specific portions of your code, while Devel::DProf gives detailed | |
79 | breakdowns of where your code spends its time. | |
80 | ||
92c2ed05 GS |
81 | Here's a sample use of Benchmark: |
82 | ||
83 | use Benchmark; | |
84 | ||
85 | @junk = `cat /etc/motd`; | |
86 | $count = 10_000; | |
87 | ||
88 | timethese($count, { | |
89 | 'map' => sub { my @a = @junk; | |
90 | map { s/a/b/ } @a; | |
91 | return @a | |
92 | }, | |
93 | 'for' => sub { my @a = @junk; | |
94 | local $_; | |
95 | for (@a) { s/a/b/ }; | |
96 | return @a }, | |
97 | }); | |
98 | ||
99 | This is what it prints (on one machine--your results will be dependent | |
100 | on your hardware, operating system, and the load on your machine): | |
101 | ||
102 | Benchmark: timing 10000 iterations of for, map... | |
103 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) | |
104 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) | |
105 | ||
65acb1b1 TC |
106 | Be aware that a good benchmark is very hard to write. It only tests the |
107 | data you give it, and really proves little about differing complexities | |
108 | of contrasting algorithms. | |
109 | ||
68dc0745 | 110 | =head2 How do I cross-reference my Perl programs? |
111 | ||
112 | The B::Xref module, shipped with the new, alpha-release Perl compiler | |
5a964f20 TC |
113 | (not the general distribution prior to the 5.005 release), can be used |
114 | to generate cross-reference reports for Perl programs. | |
68dc0745 | 115 | |
c8db1d39 | 116 | perl -MO=Xref[,OPTIONS] scriptname.plx |
68dc0745 | 117 | |
118 | =head2 Is there a pretty-printer (formatter) for Perl? | |
119 | ||
92c2ed05 GS |
120 | There is no program that will reformat Perl as much as indent(1) does |
121 | for C. The complex feedback between the scanner and the parser (this | |
122 | feedback is what confuses the vgrind and emacs programs) makes it | |
68dc0745 | 123 | challenging at best to write a stand-alone Perl parser. |
124 | ||
125 | Of course, if you simply follow the guidelines in L<perlstyle>, you | |
92c2ed05 GS |
126 | shouldn't need to reformat. The habit of formatting your code as you |
127 | write it will help prevent bugs. Your editor can and should help you | |
128 | with this. The perl-mode for emacs can provide a remarkable amount of | |
129 | help with most (but not all) code, and even less programmable editors | |
65acb1b1 TC |
130 | can provide significant assistance. Tom swears by the following |
131 | settings in vi and its clones: | |
132 | ||
133 | set ai sw=4 | |
d92eb7b0 | 134 | map! ^O {^M}^[O^T |
65acb1b1 TC |
135 | |
136 | Now put that in your F<.exrc> file (replacing the caret characters | |
137 | with control characters) and away you go. In insert mode, ^T is | |
138 | for indenting, ^D is for undenting, and ^O is for blockdenting -- | |
139 | as it were. If you haven't used the last one, you're missing | |
140 | a lot. A more complete example, with comments, can be found at | |
141 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz | |
92c2ed05 | 142 | |
65acb1b1 | 143 | If you are used to using the I<vgrind> program for printing out nice code |
92c2ed05 | 144 | to a laser printer, you can take a stab at this using |
68dc0745 | 145 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
146 | results are not particularly satisfying for sophisticated code. | |
147 | ||
87275199 | 148 | The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things |
65acb1b1 TC |
149 | related to generating nicely printed output of documents. |
150 | ||
d92eb7b0 | 151 | =head2 Is there a ctags for Perl? |
68dc0745 | 152 | |
d92eb7b0 | 153 | There's a simple one at |
68dc0745 | 154 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
65acb1b1 TC |
155 | the trick. And if not, it's easy to hack into what you want. |
156 | ||
157 | =head2 Is there an IDE or Windows Perl Editor? | |
158 | ||
d92eb7b0 GS |
159 | If you're on Unix, you already have an IDE -- Unix itself. This powerful |
160 | IDE derives from its interoperability, flexibility, and configurability. | |
161 | If you really want to get a feel for Unix-qua-IDE, the best thing to do | |
162 | is to find some high-powered programmer whose native language is Unix. | |
163 | Find someone who has been at this for many years, and just sit back | |
164 | and watch them at work. They have created their own IDE, one that | |
165 | suits their own tastes and aptitudes. Quietly observe them edit files, | |
166 | move them around, compile them, debug them, test them, etc. The entire | |
167 | development *is* integrated, like a top-of-the-line German sports car: | |
168 | functional, powerful, and elegant. You will be absolutely astonished | |
169 | at the speed and ease exhibited by the native speaker of Unix in his | |
170 | home territory. The art and skill of a virtuoso can only be seen to be | |
171 | believed. That is the path to mastery -- all these cobbled little IDEs | |
172 | are expensive toys designed to sell a flashy demo using cheap tricks, | |
173 | and being optimized for immediate but shallow understanding rather than | |
174 | enduring use, are but a dim palimpsest of real tools. | |
175 | ||
176 | In short, you just have to learn the toolbox. However, if you're not | |
177 | on Unix, then your vendor probably didn't bother to provide you with | |
178 | a proper toolbox on the so-called complete system that you forked out | |
179 | your hard-earned cash on. | |
180 | ||
181 | PerlBuilder (XXX URL to follow) is an integrated development environment | |
182 | for Windows that supports Perl development. Perl programs are just plain | |
183 | text, though, so you could download emacs for Windows (???) or a vi clone | |
87275199 | 184 | (vim) which runs on for win32 (http://www.cs.vu.nl/%7Etmgil/vi.html). |
d92eb7b0 GS |
185 | If you're transferring Windows files to Unix, be sure to transfer in |
186 | ASCII mode so the ends of lines are appropriately mangled. | |
68dc0745 | 187 | |
188 | =head2 Where can I get Perl macros for vi? | |
189 | ||
190 | For a complete version of Tom Christiansen's vi configuration file, | |
65acb1b1 | 191 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz, |
5a964f20 TC |
192 | the standard benchmark file for vi emulators. This runs best with nvi, |
193 | the current version of vi out of Berkeley, which incidentally can be built | |
194 | with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc. | |
68dc0745 | 195 | |
196 | =head2 Where can I get perl-mode for emacs? | |
197 | ||
198 | Since Emacs version 19 patchlevel 22 or so, there have been both a | |
87275199 | 199 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 | 200 | come with the standard Emacs 19 distribution. |
201 | ||
87275199 | 202 | In the Perl source directory, you'll find a directory called "emacs", |
68dc0745 | 203 | which contains a cperl-mode that color-codes keywords, provides |
204 | context-sensitive help, and other nifty things. | |
205 | ||
92c2ed05 | 206 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 | 207 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 | 208 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 | 209 | shouldn't be an issue. |
68dc0745 | 210 | |
211 | =head2 How can I use curses with Perl? | |
212 | ||
213 | The Curses module from CPAN provides a dynamically loadable object | |
5a964f20 TC |
214 | module interface to a curses library. A small demo can be found at the |
215 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; | |
216 | this program repeats a command and updates the screen as needed, rendering | |
217 | B<rep ps axu> similar to B<top>. | |
68dc0745 | 218 | |
219 | =head2 How can I use X or Tk with Perl? | |
220 | ||
5a964f20 TC |
221 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
222 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface | |
223 | to the Athena Widget set. Both are available from CPAN. See the | |
224 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ | |
68dc0745 | 225 | |
92c2ed05 | 226 | Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at |
87275199 | 227 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
92c2ed05 GS |
228 | Guide available at |
229 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the | |
230 | online manpages at | |
87275199 | 231 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 | 232 | |
68dc0745 | 233 | =head2 How can I generate simple menus without using CGI or Tk? |
234 | ||
235 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz | |
236 | module, which is curses-based, can help with this. | |
237 | ||
68dc0745 | 238 | =head2 What is undump? |
239 | ||
240 | See the next questions. | |
241 | ||
242 | =head2 How can I make my Perl program run faster? | |
243 | ||
92c2ed05 GS |
244 | The best way to do this is to come up with a better algorithm. This |
245 | can often make a dramatic difference. Chapter 8 in the Camel has some | |
246 | efficiency tips in it you might want to look at. Jon Bentley's book | |
247 | ``Programming Pearls'' (that's not a misspelling!) has some good tips | |
248 | on optimization, too. Advice on benchmarking boils down to: benchmark | |
249 | and profile to make sure you're optimizing the right part, look for | |
250 | better algorithms instead of microtuning your code, and when all else | |
251 | fails consider just buying faster hardware. | |
68dc0745 | 252 | |
92c2ed05 | 253 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 | 254 | AutoSplit and AutoLoader modules in the standard distribution for |
255 | that. Or you could locate the bottleneck and think about writing just | |
256 | that part in C, the way we used to take bottlenecks in C code and | |
257 | write them in assembler. Similar to rewriting in C is the use of | |
258 | modules that have critical sections written in C (for instance, the | |
259 | PDL module from CPAN). | |
260 | ||
261 | In some cases, it may be worth it to use the backend compiler to | |
262 | produce byte code (saving compilation time) or compile into C, which | |
263 | will certainly save compilation time and sometimes a small amount (but | |
264 | not much) execution time. See the question about compiling your Perl | |
92c2ed05 GS |
265 | programs for more on the compiler--the wins aren't as obvious as you'd |
266 | hope. | |
68dc0745 | 267 | |
92c2ed05 | 268 | If you're currently linking your perl executable to a shared I<libc.so>, |
68dc0745 | 269 | you can often gain a 10-25% performance benefit by rebuilding it to |
270 | link with a static libc.a instead. This will make a bigger perl | |
271 | executable, but your Perl programs (and programmers) may thank you for | |
272 | it. See the F<INSTALL> file in the source distribution for more | |
273 | information. | |
274 | ||
275 | Unsubstantiated reports allege that Perl interpreters that use sfio | |
87275199 | 276 | outperform those that don't (for I/O intensive applications). To try |
68dc0745 | 277 | this, see the F<INSTALL> file in the source distribution, especially |
87275199 | 278 | the ``Selecting File I/O mechanisms'' section. |
68dc0745 | 279 | |
280 | The undump program was an old attempt to speed up your Perl program | |
281 | by storing the already-compiled form to disk. This is no longer | |
282 | a viable option, as it only worked on a few architectures, and | |
283 | wasn't a good solution anyway. | |
284 | ||
285 | =head2 How can I make my Perl program take less memory? | |
286 | ||
287 | When it comes to time-space tradeoffs, Perl nearly always prefers to | |
288 | throw memory at a problem. Scalars in Perl use more memory than | |
65acb1b1 | 289 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 | 290 | there's still a lot to be done, recent releases have been addressing |
291 | these issues. For example, as of 5.004, duplicate hash keys are | |
292 | shared amongst all hashes using them, so require no reallocation. | |
293 | ||
294 | In some cases, using substr() or vec() to simulate arrays can be | |
295 | highly beneficial. For example, an array of a thousand booleans will | |
296 | take at least 20,000 bytes of space, but it can be turned into one | |
297 | 125-byte bit vector for a considerable memory savings. The standard | |
298 | Tie::SubstrHash module can also help for certain types of data | |
299 | structure. If you're working with specialist data structures | |
300 | (matrices, for instance) modules that implement these in C may use | |
301 | less memory than equivalent Perl modules. | |
302 | ||
303 | Another thing to try is learning whether your Perl was compiled with | |
54310121 | 304 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 | 305 | is, try using the other one and see whether this makes a difference. |
306 | Information about malloc is in the F<INSTALL> file in the source | |
307 | distribution. You can find out whether you are using perl's malloc by | |
308 | typing C<perl -V:usemymalloc>. | |
309 | ||
310 | =head2 Is it unsafe to return a pointer to local data? | |
311 | ||
312 | No, Perl's garbage collection system takes care of this. | |
313 | ||
314 | sub makeone { | |
315 | my @a = ( 1 .. 10 ); | |
316 | return \@a; | |
317 | } | |
318 | ||
319 | for $i ( 1 .. 10 ) { | |
320 | push @many, makeone(); | |
321 | } | |
322 | ||
323 | print $many[4][5], "\n"; | |
324 | ||
325 | print "@many\n"; | |
326 | ||
327 | =head2 How can I free an array or hash so my program shrinks? | |
328 | ||
c8db1d39 TC |
329 | You can't. On most operating systems, memory allocated to a program |
330 | can never be returned to the system. That's why long-running programs | |
65acb1b1 TC |
331 | sometimes re-exec themselves. Some operating systems (notably, |
332 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no | |
333 | longer used, but it doesn't appear to happen with Perl (yet). The Mac | |
334 | appears to be the only platform that will reliably (albeit, slowly) | |
335 | return memory to the OS. | |
336 | ||
337 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef | |
338 | $scalar> will return memory to the system, while on Solaris 2.6 it | |
339 | won't. In general, try it yourself and see. | |
68dc0745 | 340 | |
341 | However, judicious use of my() on your variables will help make sure | |
342 | that they go out of scope so that Perl can free up their storage for | |
92c2ed05 | 343 | use in other parts of your program. A global variable, of course, never |
68dc0745 | 344 | goes out of scope, so you can't get its space automatically reclaimed, |
345 | although undef()ing and/or delete()ing it will achieve the same effect. | |
46fc3d4c | 346 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 | 347 | or should be worrying about much in Perl, but even this capability |
348 | (preallocation of data types) is in the works. | |
349 | ||
350 | =head2 How can I make my CGI script more efficient? | |
351 | ||
352 | Beyond the normal measures described to make general Perl programs | |
353 | faster or smaller, a CGI program has additional issues. It may be run | |
354 | several times per second. Given that each time it runs it will need | |
46fc3d4c | 355 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 | 356 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c | 357 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 | 358 | |
92c2ed05 GS |
359 | There are two popular ways to avoid this overhead. One solution |
360 | involves running the Apache HTTP server (available from | |
68dc0745 | 361 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
92c2ed05 GS |
362 | plugin modules. |
363 | ||
364 | With mod_perl and the Apache::Registry module (distributed with | |
365 | mod_perl), httpd will run with an embedded Perl interpreter which | |
366 | pre-compiles your script and then executes it within the same address | |
367 | space without forking. The Apache extension also gives Perl access to | |
368 | the internal server API, so modules written in Perl can do just about | |
369 | anything a module written in C can. For more on mod_perl, see | |
370 | http://perl.apache.org/ | |
371 | ||
65acb1b1 | 372 | With the FCGI module (from CPAN) and the mod_fastcgi |
87275199 GS |
373 | module (available from http://www.fastcgi.com/) each of your Perl |
374 | programs becomes a permanent CGI daemon process. | |
68dc0745 | 375 | |
376 | Both of these solutions can have far-reaching effects on your system | |
87275199 | 377 | and on the way you write your CGI programs, so investigate them with |
68dc0745 | 378 | care. |
379 | ||
92c2ed05 | 380 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 | 381 | |
65acb1b1 | 382 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
6cecdcac | 383 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/) might |
c8db1d39 | 384 | also be worth looking at. It will allow you to increase the performance |
87275199 GS |
385 | of your Perl programs, up to 25 times faster than normal CGI Perl by |
386 | running in persistent Perl mode, or 4 to 5 times faster without any | |
387 | modification to your existing CGI programs. Fully functional evaluation | |
c8db1d39 TC |
388 | copies are available from the web site. |
389 | ||
68dc0745 | 390 | =head2 How can I hide the source for my Perl program? |
391 | ||
392 | Delete it. :-) Seriously, there are a number of (mostly | |
92c2ed05 | 393 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 | 394 | |
395 | First of all, however, you I<can't> take away read permission, because | |
396 | the source code has to be readable in order to be compiled and | |
397 | interpreted. (That doesn't mean that a CGI script's source is | |
92c2ed05 GS |
398 | readable by people on the web, though, only by people with access to |
399 | the filesystem) So you have to leave the permissions at the socially | |
400 | friendly 0755 level. | |
68dc0745 | 401 | |
402 | Some people regard this as a security problem. If your program does | |
403 | insecure things, and relies on people not knowing how to exploit those | |
404 | insecurities, it is not secure. It is often possible for someone to | |
405 | determine the insecure things and exploit them without viewing the | |
406 | source. Security through obscurity, the name for hiding your bugs | |
407 | instead of fixing them, is little security indeed. | |
408 | ||
92c2ed05 | 409 | You can try using encryption via source filters (Filter::* from CPAN), |
65acb1b1 TC |
410 | but any decent programmer will be able to decrypt it. You can try using |
411 | the byte code compiler and interpreter described below, but the curious | |
412 | might still be able to de-compile it. You can try using the native-code | |
413 | compiler described below, but crackers might be able to disassemble it. | |
414 | These pose varying degrees of difficulty to people wanting to get at | |
415 | your code, but none can definitively conceal it (this is true of every | |
68dc0745 | 416 | language, not just Perl). |
417 | ||
418 | If you're concerned about people profiting from your code, then the | |
d92eb7b0 | 419 | bottom line is that nothing but a restrictive license will give you |
68dc0745 | 420 | legal security. License your software and pepper it with threatening |
92c2ed05 | 421 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 | 422 | Your access to it does not give you permission to use it blah blah |
92c2ed05 | 423 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 | 424 | you want to be sure your license's wording will stand up in court. |
68dc0745 | 425 | |
54310121 | 426 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 | 427 | |
428 | Malcolm Beattie has written a multifunction backend compiler, | |
5e3006a4 GS |
429 | available from CPAN, that can do both these things. It is included |
430 | in the perl5.005 release, but is still considered experimental. | |
431 | This means it's fun to play with if you're a programmer but not | |
432 | really for people looking for turn-key solutions. | |
68dc0745 | 433 | |
92c2ed05 GS |
434 | Merely compiling into C does not in and of itself guarantee that your |
435 | code will run very much faster. That's because except for lucky cases | |
436 | where a lot of native type inferencing is possible, the normal Perl | |
437 | run time system is still present and so your program will take just as | |
438 | long to run and be just as big. Most programs save little more than | |
439 | compilation time, leaving execution no more than 10-30% faster. A few | |
440 | rare programs actually benefit significantly (like several times | |
441 | faster), but this takes some tweaking of your code. | |
68dc0745 | 442 | |
68dc0745 | 443 | You'll probably be astonished to learn that the current version of the |
444 | compiler generates a compiled form of your script whose executable is | |
445 | just as big as the original perl executable, and then some. That's | |
446 | because as currently written, all programs are prepared for a full | |
447 | eval() statement. You can tremendously reduce this cost by building a | |
92c2ed05 | 448 | shared I<libperl.so> library and linking against that. See the |
87275199 | 449 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 | 450 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 | 451 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 | 452 | size! |
453 | ||
5a964f20 TC |
454 | In general, the compiler will do nothing to make a Perl program smaller, |
455 | faster, more portable, or more secure. In fact, it will usually hurt | |
456 | all of those. The executable will be bigger, your VM system may take | |
457 | longer to load the whole thing, the binary is fragile and hard to fix, | |
458 | and compilation never stopped software piracy in the form of crackers, | |
459 | viruses, or bootleggers. The real advantage of the compiler is merely | |
460 | packaging, and once you see the size of what it makes (well, unless | |
461 | you use a shared I<libperl.so>), you'll probably want a complete | |
5e3006a4 | 462 | Perl install anyway. |
5a964f20 | 463 | |
65acb1b1 TC |
464 | =head2 How can I compile Perl into Java? |
465 | ||
466 | You can't. Not yet, anyway. You can integrate Java and Perl with the | |
467 | Perl Resource Kit from O'Reilly and Associates. See | |
468 | http://www.oreilly.com/catalog/prkunix/ for more information. | |
87275199 | 469 | The Java interface will be supported in the core 5.6 release |
65acb1b1 TC |
470 | of Perl. |
471 | ||
92c2ed05 | 472 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 | 473 | |
474 | For OS/2 just use | |
475 | ||
476 | extproc perl -S -your_switches | |
477 | ||
478 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's | |
46fc3d4c | 479 | `extproc' handling). For DOS one should first invent a corresponding |
68dc0745 | 480 | batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the |
481 | F<INSTALL> file in the source distribution for more information). | |
482 | ||
92c2ed05 GS |
483 | The Win95/NT installation, when using the ActiveState port of Perl, |
484 | will modify the Registry to associate the C<.pl> extension with the | |
d92eb7b0 GS |
485 | perl interpreter. If you install another port, perhaps even building |
486 | your own Win95/NT Perl from the standard sources by using a Windows port | |
d702ae42 | 487 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 GS |
488 | the Registry yourself. In addition to associating C<.pl> with the |
489 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them | |
490 | run the program C<install-linux.pl> merely by typing C<install-linux>. | |
68dc0745 | 491 | |
87275199 GS |
492 | Macintosh Perl programs will have the appropriate Creator and |
493 | Type, so that double-clicking them will invoke the Perl application. | |
68dc0745 | 494 | |
495 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just | |
496 | throw the perl interpreter into your cgi-bin directory, in order to | |
87275199 | 497 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 | 498 | security risk. Take the time to figure out how to do it correctly. |
499 | ||
87275199 | 500 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 | 501 | |
502 | Yes. Read L<perlrun> for more information. Some examples follow. | |
503 | (These assume standard Unix shell quoting rules.) | |
504 | ||
505 | # sum first and last fields | |
5a964f20 | 506 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 | 507 | |
508 | # identify text files | |
509 | perl -le 'for(@ARGV) {print if -f && -T _}' * | |
510 | ||
5a964f20 | 511 | # remove (most) comments from C program |
68dc0745 | 512 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
513 | ||
514 | # make file a month younger than today, defeating reaper daemons | |
515 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * | |
516 | ||
517 | # find first unused uid | |
518 | perl -le '$i++ while getpwuid($i); print $i' | |
519 | ||
520 | # display reasonable manpath | |
521 | echo $PATH | perl -nl -072 -e ' | |
522 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' | |
523 | ||
87275199 | 524 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 | 525 | |
87275199 | 526 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 | 527 | |
528 | The problem is usually that the command interpreters on those systems | |
529 | have rather different ideas about quoting than the Unix shells under | |
530 | which the one-liners were created. On some systems, you may have to | |
531 | change single-quotes to double ones, which you must I<NOT> do on Unix | |
532 | or Plan9 systems. You might also have to change a single % to a %%. | |
533 | ||
534 | For example: | |
535 | ||
536 | # Unix | |
537 | perl -e 'print "Hello world\n"' | |
538 | ||
46fc3d4c | 539 | # DOS, etc. |
68dc0745 | 540 | perl -e "print \"Hello world\n\"" |
541 | ||
46fc3d4c | 542 | # Mac |
68dc0745 | 543 | print "Hello world\n" |
544 | (then Run "Myscript" or Shift-Command-R) | |
545 | ||
546 | # VMS | |
547 | perl -e "print ""Hello world\n""" | |
548 | ||
92c2ed05 GS |
549 | The problem is that none of this is reliable: it depends on the |
550 | command interpreter. Under Unix, the first two often work. Under DOS, | |
551 | it's entirely possible neither works. If 4DOS was the command shell, | |
552 | you'd probably have better luck like this: | |
68dc0745 | 553 | |
554 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
555 | ||
46fc3d4c | 556 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 | 557 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c | 558 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 | 559 | characters as control characters. |
560 | ||
65acb1b1 TC |
561 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
562 | quotes', and `backticks`, may make one-liners easier to write. | |
563 | ||
92c2ed05 GS |
564 | There is no general solution to all of this. It is a mess, pure and |
565 | simple. Sucks to be away from Unix, huh? :-) | |
68dc0745 | 566 | |
567 | [Some of this answer was contributed by Kenneth Albanowski.] | |
568 | ||
569 | =head2 Where can I learn about CGI or Web programming in Perl? | |
570 | ||
571 | For modules, get the CGI or LWP modules from CPAN. For textbooks, | |
572 | see the two especially dedicated to web stuff in the question on | |
92c2ed05 GS |
573 | books. For problems and questions related to the web, like ``Why |
574 | do I get 500 Errors'' or ``Why doesn't it run from the browser right | |
575 | when it runs fine on the command line'', see these sources: | |
68dc0745 | 576 | |
5a964f20 TC |
577 | WWW Security FAQ |
578 | http://www.w3.org/Security/Faq/ | |
68dc0745 | 579 | |
5a964f20 TC |
580 | Web FAQ |
581 | http://www.boutell.com/faq/ | |
68dc0745 | 582 | |
5a964f20 | 583 | CGI FAQ |
6cecdcac | 584 | http://www.webthing.com/tutorials/cgifaq.html |
68dc0745 | 585 | |
5a964f20 TC |
586 | HTTP Spec |
587 | http://www.w3.org/pub/WWW/Protocols/HTTP/ | |
588 | ||
589 | HTML Spec | |
590 | http://www.w3.org/TR/REC-html40/ | |
591 | http://www.w3.org/pub/WWW/MarkUp/ | |
592 | ||
593 | CGI Spec | |
594 | http://www.w3.org/CGI/ | |
595 | ||
596 | CGI Security FAQ | |
597 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt | |
68dc0745 | 598 | |
68dc0745 | 599 | |
600 | =head2 Where can I learn about object-oriented Perl programming? | |
601 | ||
87275199 | 602 | A good place to start is L<perltoot>, and you can use L<perlobj> and |
68dc0745 | 603 | L<perlbot> for reference. Perltoot didn't come out until the 5.004 |
604 | release, but you can get a copy (in pod, html, or postscript) from | |
605 | http://www.perl.com/CPAN/doc/FMTEYEWTK/ . | |
606 | ||
607 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
608 | ||
609 | If you want to call C from Perl, start with L<perlxstut>, | |
610 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to | |
611 | call Perl from C, then read L<perlembed>, L<perlcall>, and | |
612 | L<perlguts>. Don't forget that you can learn a lot from looking at | |
613 | how the authors of existing extension modules wrote their code and | |
614 | solved their problems. | |
615 | ||
616 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in | |
617 | my C program, what am I doing wrong? | |
618 | ||
619 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If | |
620 | the tests pass, read the pods again and again and again. If they | |
87275199 | 621 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 | 622 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
623 | ||
624 | =head2 When I tried to run my script, I got this message. What does it | |
625 | mean? | |
626 | ||
87275199 GS |
627 | A complete list of Perl's error messages and warnings with explanatory |
628 | text can be found in L<perldiag>. You can also use the splain program | |
629 | (distributed with Perl) to explain the error messages: | |
68dc0745 | 630 | |
631 | perl program 2>diag.out | |
632 | splain [-v] [-p] diag.out | |
633 | ||
634 | or change your program to explain the messages for you: | |
635 | ||
636 | use diagnostics; | |
637 | ||
638 | or | |
639 | ||
640 | use diagnostics -verbose; | |
641 | ||
642 | =head2 What's MakeMaker? | |
643 | ||
87275199 | 644 | This module (part of the standard Perl distribution) is designed to |
68dc0745 | 645 | write a Makefile for an extension module from a Makefile.PL. For more |
646 | information, see L<ExtUtils::MakeMaker>. | |
647 | ||
648 | =head1 AUTHOR AND COPYRIGHT | |
649 | ||
65acb1b1 | 650 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 TC |
651 | All rights reserved. |
652 | ||
c8db1d39 | 653 | When included as an integrated part of the Standard Distribution |
d92eb7b0 GS |
654 | of Perl or of its documentation (printed or otherwise), this works is |
655 | covered under Perl's Artistic License. For separate distributions of | |
c8db1d39 TC |
656 | all or part of this FAQ outside of that, see L<perlfaq>. |
657 | ||
87275199 | 658 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
659 | domain. You are permitted and encouraged to use this code and any |
660 | derivatives thereof in your own programs for fun or for profit as you | |
661 | see fit. A simple comment in the code giving credit to the FAQ would | |
662 | be courteous but is not required. |