Commit | Line | Data |
---|---|---|
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 | 51 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
a6dd486b | 52 | to detect 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 | |
a6dd486b | 57 | variables with C<my>, C<our>, or C<use vars>. |
68dc0745 | 58 | |
a6dd486b JB |
59 | Did you check the return values of each and every system call? The operating |
60 | system (and thus Perl) tells you whether they worked, and if not | |
92c2ed05 | 61 | why. |
68dc0745 | 62 | |
92c2ed05 GS |
63 | open(FH, "> /etc/cantwrite") |
64 | or die "Couldn't write to /etc/cantwrite: $!\n"; | |
68dc0745 | 65 | |
92c2ed05 | 66 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
a6dd486b | 67 | programmers and even has sections for those of you who are upgrading |
92c2ed05 GS |
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 | ||
e083a89c | 76 | You should get the Devel::DProf module from the standard distribution |
733271b5 PK |
77 | (or separately on CPAN) and also use Benchmark.pm from the standard |
78 | distribution. The Benchmark module lets you time specific portions of | |
79 | your code, while Devel::DProf gives detailed breakdowns of where your | |
e083a89c | 80 | code spends its time. |
68dc0745 | 81 | |
92c2ed05 GS |
82 | Here's a sample use of Benchmark: |
83 | ||
84 | use Benchmark; | |
85 | ||
86 | @junk = `cat /etc/motd`; | |
87 | $count = 10_000; | |
88 | ||
89 | timethese($count, { | |
90 | 'map' => sub { my @a = @junk; | |
91 | map { s/a/b/ } @a; | |
92 | return @a | |
93 | }, | |
94 | 'for' => sub { my @a = @junk; | |
95 | local $_; | |
96 | for (@a) { s/a/b/ }; | |
97 | return @a }, | |
98 | }); | |
99 | ||
100 | This is what it prints (on one machine--your results will be dependent | |
101 | on your hardware, operating system, and the load on your machine): | |
102 | ||
103 | Benchmark: timing 10000 iterations of for, map... | |
104 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) | |
105 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) | |
106 | ||
65acb1b1 | 107 | Be aware that a good benchmark is very hard to write. It only tests the |
a6dd486b | 108 | data you give it and proves little about the differing complexities |
65acb1b1 TC |
109 | of contrasting algorithms. |
110 | ||
68dc0745 | 111 | =head2 How do I cross-reference my Perl programs? |
112 | ||
113 | The B::Xref module, shipped with the new, alpha-release Perl compiler | |
5a964f20 TC |
114 | (not the general distribution prior to the 5.005 release), can be used |
115 | to generate cross-reference reports for Perl programs. | |
68dc0745 | 116 | |
c8db1d39 | 117 | perl -MO=Xref[,OPTIONS] scriptname.plx |
68dc0745 | 118 | |
119 | =head2 Is there a pretty-printer (formatter) for Perl? | |
120 | ||
92c2ed05 GS |
121 | There is no program that will reformat Perl as much as indent(1) does |
122 | for C. The complex feedback between the scanner and the parser (this | |
123 | feedback is what confuses the vgrind and emacs programs) makes it | |
68dc0745 | 124 | challenging at best to write a stand-alone Perl parser. |
125 | ||
126 | Of course, if you simply follow the guidelines in L<perlstyle>, you | |
92c2ed05 GS |
127 | shouldn't need to reformat. The habit of formatting your code as you |
128 | write it will help prevent bugs. Your editor can and should help you | |
a6dd486b JB |
129 | with this. The perl-mode or newer cperl-mode for emacs can provide |
130 | remarkable amounts of help with most (but not all) code, and even less | |
131 | programmable editors can provide significant assistance. Tom swears | |
132 | by the following settings in vi and its clones: | |
65acb1b1 TC |
133 | |
134 | set ai sw=4 | |
d92eb7b0 | 135 | map! ^O {^M}^[O^T |
65acb1b1 TC |
136 | |
137 | Now put that in your F<.exrc> file (replacing the caret characters | |
138 | with control characters) and away you go. In insert mode, ^T is | |
a6dd486b | 139 | for indenting, ^D is for undenting, and ^O is for blockdenting-- |
65acb1b1 TC |
140 | as it were. If you haven't used the last one, you're missing |
141 | a lot. A more complete example, with comments, can be found at | |
142 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz | |
92c2ed05 | 143 | |
65acb1b1 | 144 | If you are used to using the I<vgrind> program for printing out nice code |
92c2ed05 | 145 | to a laser printer, you can take a stab at this using |
68dc0745 | 146 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
147 | results are not particularly satisfying for sophisticated code. | |
148 | ||
87275199 | 149 | The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things |
65acb1b1 TC |
150 | related to generating nicely printed output of documents. |
151 | ||
d92eb7b0 | 152 | =head2 Is there a ctags for Perl? |
68dc0745 | 153 | |
d92eb7b0 | 154 | There's a simple one at |
68dc0745 | 155 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
65acb1b1 TC |
156 | the trick. And if not, it's easy to hack into what you want. |
157 | ||
158 | =head2 Is there an IDE or Windows Perl Editor? | |
159 | ||
6641ed39 JH |
160 | Perl programs are just plain text, so any editor will do. |
161 | ||
6641ed39 JH |
162 | If you're on Unix, you already have an IDE--Unix itself. The UNIX |
163 | philosophy is the philosophy of several small tools that each do one | |
164 | thing and do it well. It's like a carpenter's toolbox. | |
165 | ||
68fbfbd7 JH |
166 | If you want a Windows IDE, check the following: |
167 | ||
168 | =over 4 | |
169 | ||
170 | =item CodeMagicCD | |
171 | ||
172 | http://www.codemagiccd.com/ | |
173 | ||
174 | =item Komodo | |
175 | ||
5a13f98a JH |
176 | ActiveState's cross-platform, multi-language IDE has Perl support, |
177 | including a regular expression debugger and remote debugging | |
178 | (http://www.ActiveState.com/Products/Komodo/index.html). | |
68fbfbd7 | 179 | (Visual Perl, a Visual Studio.NET plug-in is currently (early 2001) |
5a13f98a | 180 | in beta (http://www.ActiveState.com/Products/VisualPerl/index.html)). |
68fbfbd7 JH |
181 | |
182 | =item The Object System | |
183 | ||
8782d048 | 184 | (http://www.castlelink.co.uk/object_system/) is a Perl web |
614a1598 | 185 | applications development IDE. |
8782d048 | 186 | |
68fbfbd7 JH |
187 | =item Perl code magic |
188 | ||
189 | (http://www.petes-place.com/codemagic.html). | |
190 | ||
191 | =item visiPerl+ | |
192 | ||
193 | http://helpconsulting.net/visiperl/, from Help Consulting. | |
194 | ||
195 | =back | |
196 | ||
5a13f98a | 197 | For editors: if you're on Unix you probably have vi or a vi clone already, |
6641ed39 | 198 | and possibly an emacs too, so you may not need to download anything. |
5a13f98a | 199 | In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the |
6641ed39 JH |
200 | best available Perl editing mode in any editor. |
201 | ||
68fbfbd7 JH |
202 | For Windows editors: you can download an Emacs |
203 | ||
204 | =over 4 | |
205 | ||
206 | =item GNU Emacs | |
207 | ||
208 | http://www.gnu.org/software/emacs/windows/ntemacs.html | |
209 | ||
210 | =item MicroEMACS | |
211 | ||
212 | http://members.nbci.com/uemacs/ | |
213 | ||
214 | =item XEmacs | |
215 | ||
216 | http://www.xemacs.org/Download/index.html | |
217 | ||
218 | =back | |
219 | ||
220 | or a vi clone such as | |
221 | ||
222 | =over 4 | |
223 | ||
224 | =item Elvis | |
225 | ||
226 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ | |
227 | ||
228 | =item Vile | |
229 | ||
230 | http://vile.cx/ | |
231 | ||
232 | =item Vim | |
233 | ||
234 | http://www.vim.org/ | |
235 | ||
236 | win32: http://www.cs.vu.nl/%7Etmgil/vi.html | |
237 | ||
238 | =back | |
239 | ||
5a13f98a JH |
240 | For vi lovers in general, Windows or elsewhere: |
241 | http://www.thomer.com/thomer/vi/vi.html. | |
6641ed39 JH |
242 | |
243 | nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is | |
5a13f98a | 244 | yet another vi clone, unfortunately not available for Windows, but in |
6641ed39 JH |
245 | UNIX platforms you might be interested in trying it out, firstly because |
246 | strictly speaking it is not a vi clone, it is the real vi, or the new | |
247 | incarnation of it, and secondly because you can embed Perl inside it | |
248 | to use Perl as the scripting language. nvi is not alone in this, | |
7c82de66 | 249 | though: at least also vim and vile offer an embedded Perl. |
614a1598 | 250 | |
68fbfbd7 JH |
251 | The following are Win32 multilanguage editor/IDESs that support Perl: |
252 | ||
253 | =over 4 | |
254 | ||
255 | =item Codewright | |
256 | ||
257 | http://www.starbase.com/ | |
258 | ||
259 | =item MultiEdit | |
260 | ||
261 | http://www.MultiEdit.com/ | |
262 | ||
263 | =item SlickEdit | |
264 | ||
265 | http://www.slickedit.com/ | |
266 | ||
267 | =back | |
8782d048 | 268 | |
6641ed39 JH |
269 | There is also a toyedit Text widget based editor written in Perl |
270 | that is distributed with the Tk module on CPAN. The ptkdb | |
8782d048 JH |
271 | (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that |
272 | acts as a development environment of sorts. Perl Composer | |
e083a89c JH |
273 | (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk |
274 | GUI creation. | |
275 | ||
8782d048 | 276 | In addition to an editor/IDE you might be interested in a more |
68fbfbd7 JH |
277 | powerful shell environment for Win32. Your options include |
278 | ||
279 | =over 4 | |
280 | ||
281 | =item Bash | |
282 | ||
283 | from the Cygwin package (http://sources.redhat.com/cygwin/) | |
284 | ||
285 | =item Ksh | |
286 | ||
287 | from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of | |
288 | the U/WIN environment (http://www.research.att.com/sw/tools/uwin/) | |
289 | ||
290 | =item Tcsh | |
291 | ||
292 | ftp://ftp.astron.com/pub/tcsh/, see also | |
293 | http://www.primate.wisc.edu/software/csh-tcsh-book/ | |
294 | ||
295 | =item Zsh | |
296 | ||
297 | ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/ | |
298 | ||
299 | =back | |
300 | ||
614a1598 JH |
301 | MKS and U/WIN are commercial (U/WIN is free for educational and |
302 | research purposes), Cygwin is covered by the GNU Public License (but | |
303 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all | |
304 | contain (in addition to the shells) a comprehensive set of standard | |
305 | UNIX toolkit utilities. | |
8782d048 | 306 | |
5a13f98a JH |
307 | If you're transferring text files between Unix and Windows using FTP |
308 | be sure to transfer them in ASCII mode so the ends of lines are | |
309 | appropriately converted. | |
310 | ||
e083a89c JH |
311 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
312 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application | |
733271b5 | 313 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
68fbfbd7 JH |
314 | no 32k limit). |
315 | ||
316 | =over 4 | |
317 | ||
318 | =item BBEdit and BBEdit Lite | |
319 | ||
320 | are text editors for Mac OS that have a Perl sensitivity mode | |
321 | (http://web.barebones.com/). | |
322 | ||
323 | =item Alpha | |
324 | ||
325 | is an editor, written and extensible in Tcl, that nonetheless has | |
733271b5 | 326 | built in support for several popular markup and programming languages |
68fbfbd7 JH |
327 | including Perl and HTML (http://alpha.olm.net/). |
328 | ||
329 | =back | |
330 | ||
331 | Pepper and Pe are programming language sensitive text editors for Mac | |
332 | OS X and BeOS respectively (http://www.hekkelman.com/). | |
68dc0745 | 333 | |
334 | =head2 Where can I get Perl macros for vi? | |
335 | ||
336 | For a complete version of Tom Christiansen's vi configuration file, | |
a6dd486b JB |
337 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
338 | the standard benchmark file for vi emulators. The file runs best with nvi, | |
5a964f20 | 339 | the current version of vi out of Berkeley, which incidentally can be built |
a6dd486b | 340 | with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc. |
68dc0745 | 341 | |
342 | =head2 Where can I get perl-mode for emacs? | |
343 | ||
344 | Since Emacs version 19 patchlevel 22 or so, there have been both a | |
87275199 | 345 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 | 346 | come with the standard Emacs 19 distribution. |
347 | ||
87275199 | 348 | In the Perl source directory, you'll find a directory called "emacs", |
68dc0745 | 349 | which contains a cperl-mode that color-codes keywords, provides |
350 | context-sensitive help, and other nifty things. | |
351 | ||
92c2ed05 | 352 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 | 353 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 | 354 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 | 355 | shouldn't be an issue. |
68dc0745 | 356 | |
357 | =head2 How can I use curses with Perl? | |
358 | ||
359 | The Curses module from CPAN provides a dynamically loadable object | |
5a964f20 TC |
360 | module interface to a curses library. A small demo can be found at the |
361 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; | |
362 | this program repeats a command and updates the screen as needed, rendering | |
363 | B<rep ps axu> similar to B<top>. | |
68dc0745 | 364 | |
365 | =head2 How can I use X or Tk with Perl? | |
366 | ||
5a964f20 TC |
367 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
368 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface | |
369 | to the Athena Widget set. Both are available from CPAN. See the | |
370 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ | |
68dc0745 | 371 | |
a6dd486b | 372 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
87275199 | 373 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
92c2ed05 GS |
374 | Guide available at |
375 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the | |
376 | online manpages at | |
87275199 | 377 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 | 378 | |
68dc0745 | 379 | =head2 How can I generate simple menus without using CGI or Tk? |
380 | ||
381 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz | |
382 | module, which is curses-based, can help with this. | |
383 | ||
68dc0745 | 384 | =head2 What is undump? |
385 | ||
a6dd486b | 386 | See the next question on ``How can I make my Perl program run faster?'' |
68dc0745 | 387 | |
388 | =head2 How can I make my Perl program run faster? | |
389 | ||
92c2ed05 | 390 | The best way to do this is to come up with a better algorithm. This |
b73a15ae | 391 | can often make a dramatic difference. Jon Bentley's book |
92c2ed05 GS |
392 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
393 | on optimization, too. Advice on benchmarking boils down to: benchmark | |
394 | and profile to make sure you're optimizing the right part, look for | |
395 | better algorithms instead of microtuning your code, and when all else | |
396 | fails consider just buying faster hardware. | |
68dc0745 | 397 | |
92c2ed05 | 398 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 | 399 | AutoSplit and AutoLoader modules in the standard distribution for |
400 | that. Or you could locate the bottleneck and think about writing just | |
401 | that part in C, the way we used to take bottlenecks in C code and | |
a6dd486b JB |
402 | write them in assembler. Similar to rewriting in C, |
403 | modules that have critical sections can be written in C (for instance, the | |
68dc0745 | 404 | PDL module from CPAN). |
405 | ||
406 | In some cases, it may be worth it to use the backend compiler to | |
407 | produce byte code (saving compilation time) or compile into C, which | |
408 | will certainly save compilation time and sometimes a small amount (but | |
409 | not much) execution time. See the question about compiling your Perl | |
92c2ed05 GS |
410 | programs for more on the compiler--the wins aren't as obvious as you'd |
411 | hope. | |
68dc0745 | 412 | |
92c2ed05 | 413 | If you're currently linking your perl executable to a shared I<libc.so>, |
68dc0745 | 414 | you can often gain a 10-25% performance benefit by rebuilding it to |
415 | link with a static libc.a instead. This will make a bigger perl | |
416 | executable, but your Perl programs (and programmers) may thank you for | |
417 | it. See the F<INSTALL> file in the source distribution for more | |
418 | information. | |
419 | ||
420 | Unsubstantiated reports allege that Perl interpreters that use sfio | |
87275199 | 421 | outperform those that don't (for I/O intensive applications). To try |
68dc0745 | 422 | this, see the F<INSTALL> file in the source distribution, especially |
87275199 | 423 | the ``Selecting File I/O mechanisms'' section. |
68dc0745 | 424 | |
425 | The undump program was an old attempt to speed up your Perl program | |
426 | by storing the already-compiled form to disk. This is no longer | |
427 | a viable option, as it only worked on a few architectures, and | |
428 | wasn't a good solution anyway. | |
429 | ||
430 | =head2 How can I make my Perl program take less memory? | |
431 | ||
432 | When it comes to time-space tradeoffs, Perl nearly always prefers to | |
433 | throw memory at a problem. Scalars in Perl use more memory than | |
65acb1b1 | 434 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 | 435 | there's still a lot to be done, recent releases have been addressing |
436 | these issues. For example, as of 5.004, duplicate hash keys are | |
437 | shared amongst all hashes using them, so require no reallocation. | |
438 | ||
439 | In some cases, using substr() or vec() to simulate arrays can be | |
440 | highly beneficial. For example, an array of a thousand booleans will | |
441 | take at least 20,000 bytes of space, but it can be turned into one | |
a6dd486b | 442 | 125-byte bit vector--a considerable memory savings. The standard |
68dc0745 | 443 | Tie::SubstrHash module can also help for certain types of data |
444 | structure. If you're working with specialist data structures | |
445 | (matrices, for instance) modules that implement these in C may use | |
446 | less memory than equivalent Perl modules. | |
447 | ||
448 | Another thing to try is learning whether your Perl was compiled with | |
54310121 | 449 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 | 450 | is, try using the other one and see whether this makes a difference. |
451 | Information about malloc is in the F<INSTALL> file in the source | |
452 | distribution. You can find out whether you are using perl's malloc by | |
453 | typing C<perl -V:usemymalloc>. | |
454 | ||
455 | =head2 Is it unsafe to return a pointer to local data? | |
456 | ||
457 | No, Perl's garbage collection system takes care of this. | |
458 | ||
459 | sub makeone { | |
460 | my @a = ( 1 .. 10 ); | |
461 | return \@a; | |
462 | } | |
463 | ||
464 | for $i ( 1 .. 10 ) { | |
465 | push @many, makeone(); | |
466 | } | |
467 | ||
468 | print $many[4][5], "\n"; | |
469 | ||
470 | print "@many\n"; | |
471 | ||
472 | =head2 How can I free an array or hash so my program shrinks? | |
473 | ||
c8db1d39 TC |
474 | You can't. On most operating systems, memory allocated to a program |
475 | can never be returned to the system. That's why long-running programs | |
65acb1b1 TC |
476 | sometimes re-exec themselves. Some operating systems (notably, |
477 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no | |
478 | longer used, but it doesn't appear to happen with Perl (yet). The Mac | |
479 | appears to be the only platform that will reliably (albeit, slowly) | |
480 | return memory to the OS. | |
481 | ||
482 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef | |
483 | $scalar> will return memory to the system, while on Solaris 2.6 it | |
484 | won't. In general, try it yourself and see. | |
68dc0745 | 485 | |
486 | However, judicious use of my() on your variables will help make sure | |
a6dd486b | 487 | that they go out of scope so that Perl can free up that space for |
92c2ed05 | 488 | use in other parts of your program. A global variable, of course, never |
68dc0745 | 489 | goes out of scope, so you can't get its space automatically reclaimed, |
490 | although undef()ing and/or delete()ing it will achieve the same effect. | |
46fc3d4c | 491 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 | 492 | or should be worrying about much in Perl, but even this capability |
493 | (preallocation of data types) is in the works. | |
494 | ||
495 | =head2 How can I make my CGI script more efficient? | |
496 | ||
497 | Beyond the normal measures described to make general Perl programs | |
498 | faster or smaller, a CGI program has additional issues. It may be run | |
499 | several times per second. Given that each time it runs it will need | |
46fc3d4c | 500 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 | 501 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c | 502 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 | 503 | |
92c2ed05 GS |
504 | There are two popular ways to avoid this overhead. One solution |
505 | involves running the Apache HTTP server (available from | |
68dc0745 | 506 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
92c2ed05 GS |
507 | plugin modules. |
508 | ||
509 | With mod_perl and the Apache::Registry module (distributed with | |
510 | mod_perl), httpd will run with an embedded Perl interpreter which | |
511 | pre-compiles your script and then executes it within the same address | |
512 | space without forking. The Apache extension also gives Perl access to | |
513 | the internal server API, so modules written in Perl can do just about | |
514 | anything a module written in C can. For more on mod_perl, see | |
515 | http://perl.apache.org/ | |
516 | ||
65acb1b1 | 517 | With the FCGI module (from CPAN) and the mod_fastcgi |
87275199 GS |
518 | module (available from http://www.fastcgi.com/) each of your Perl |
519 | programs becomes a permanent CGI daemon process. | |
68dc0745 | 520 | |
521 | Both of these solutions can have far-reaching effects on your system | |
87275199 | 522 | and on the way you write your CGI programs, so investigate them with |
68dc0745 | 523 | care. |
524 | ||
92c2ed05 | 525 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 | 526 | |
65acb1b1 | 527 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
a6dd486b JB |
528 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ ) |
529 | might also be worth looking at. It will allow you to increase the | |
530 | performance of your Perl programs, running programs up to 25 times | |
531 | faster than normal CGI Perl when running in persistent Perl mode or 4 | |
532 | to 5 times faster without any modification to your existing CGI | |
533 | programs. Fully functional evaluation copies are available from the | |
534 | web site. | |
c8db1d39 | 535 | |
68dc0745 | 536 | =head2 How can I hide the source for my Perl program? |
537 | ||
538 | Delete it. :-) Seriously, there are a number of (mostly | |
92c2ed05 | 539 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 | 540 | |
541 | First of all, however, you I<can't> take away read permission, because | |
542 | the source code has to be readable in order to be compiled and | |
543 | interpreted. (That doesn't mean that a CGI script's source is | |
a6dd486b JB |
544 | readable by people on the web, though--only by people with access to |
545 | the filesystem.) So you have to leave the permissions at the socially | |
92c2ed05 | 546 | friendly 0755 level. |
68dc0745 | 547 | |
548 | Some people regard this as a security problem. If your program does | |
a6dd486b | 549 | insecure things and relies on people not knowing how to exploit those |
68dc0745 | 550 | insecurities, it is not secure. It is often possible for someone to |
551 | determine the insecure things and exploit them without viewing the | |
552 | source. Security through obscurity, the name for hiding your bugs | |
553 | instead of fixing them, is little security indeed. | |
554 | ||
83df6a1d JH |
555 | You can try using encryption via source filters (Starting from Perl |
556 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in | |
557 | the standard distribution), but any decent programmer will be able to | |
558 | decrypt it. You can try using the byte code compiler and interpreter | |
559 | described below, but the curious might still be able to de-compile it. | |
560 | You can try using the native-code compiler described below, but | |
561 | crackers might be able to disassemble it. These pose varying degrees | |
562 | of difficulty to people wanting to get at your code, but none can | |
563 | definitively conceal it (true of every language, not just Perl). | |
68dc0745 | 564 | |
565 | If you're concerned about people profiting from your code, then the | |
d92eb7b0 | 566 | bottom line is that nothing but a restrictive license will give you |
68dc0745 | 567 | legal security. License your software and pepper it with threatening |
92c2ed05 | 568 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 | 569 | Your access to it does not give you permission to use it blah blah |
92c2ed05 | 570 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 | 571 | you want to be sure your license's wording will stand up in court. |
68dc0745 | 572 | |
54310121 | 573 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 | 574 | |
575 | Malcolm Beattie has written a multifunction backend compiler, | |
5e3006a4 GS |
576 | available from CPAN, that can do both these things. It is included |
577 | in the perl5.005 release, but is still considered experimental. | |
578 | This means it's fun to play with if you're a programmer but not | |
579 | really for people looking for turn-key solutions. | |
68dc0745 | 580 | |
92c2ed05 GS |
581 | Merely compiling into C does not in and of itself guarantee that your |
582 | code will run very much faster. That's because except for lucky cases | |
583 | where a lot of native type inferencing is possible, the normal Perl | |
a6dd486b | 584 | run-time system is still present and so your program will take just as |
92c2ed05 GS |
585 | long to run and be just as big. Most programs save little more than |
586 | compilation time, leaving execution no more than 10-30% faster. A few | |
a6dd486b | 587 | rare programs actually benefit significantly (even running several times |
92c2ed05 | 588 | faster), but this takes some tweaking of your code. |
68dc0745 | 589 | |
68dc0745 | 590 | You'll probably be astonished to learn that the current version of the |
591 | compiler generates a compiled form of your script whose executable is | |
592 | just as big as the original perl executable, and then some. That's | |
593 | because as currently written, all programs are prepared for a full | |
594 | eval() statement. You can tremendously reduce this cost by building a | |
92c2ed05 | 595 | shared I<libperl.so> library and linking against that. See the |
87275199 | 596 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 | 597 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 | 598 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 | 599 | size! |
600 | ||
5a964f20 | 601 | In general, the compiler will do nothing to make a Perl program smaller, |
a6dd486b JB |
602 | faster, more portable, or more secure. In fact, it can make your |
603 | situation worse. The executable will be bigger, your VM system may take | |
5a964f20 TC |
604 | longer to load the whole thing, the binary is fragile and hard to fix, |
605 | and compilation never stopped software piracy in the form of crackers, | |
606 | viruses, or bootleggers. The real advantage of the compiler is merely | |
607 | packaging, and once you see the size of what it makes (well, unless | |
608 | you use a shared I<libperl.so>), you'll probably want a complete | |
5e3006a4 | 609 | Perl install anyway. |
5a964f20 | 610 | |
65acb1b1 TC |
611 | =head2 How can I compile Perl into Java? |
612 | ||
a6dd486b | 613 | You can also integrate Java and Perl with the |
65acb1b1 | 614 | Perl Resource Kit from O'Reilly and Associates. See |
a6dd486b JB |
615 | http://www.oreilly.com/catalog/prkunix/ . |
616 | ||
617 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in | |
618 | development, allows Perl code to be called from Java. See jpl/README | |
619 | in the Perl source tree. | |
65acb1b1 | 620 | |
92c2ed05 | 621 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 | 622 | |
623 | For OS/2 just use | |
624 | ||
625 | extproc perl -S -your_switches | |
626 | ||
627 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's | |
46fc3d4c | 628 | `extproc' handling). For DOS one should first invent a corresponding |
a6dd486b | 629 | batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the |
68dc0745 | 630 | F<INSTALL> file in the source distribution for more information). |
631 | ||
92c2ed05 GS |
632 | The Win95/NT installation, when using the ActiveState port of Perl, |
633 | will modify the Registry to associate the C<.pl> extension with the | |
d92eb7b0 GS |
634 | perl interpreter. If you install another port, perhaps even building |
635 | your own Win95/NT Perl from the standard sources by using a Windows port | |
d702ae42 | 636 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 GS |
637 | the Registry yourself. In addition to associating C<.pl> with the |
638 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them | |
639 | run the program C<install-linux.pl> merely by typing C<install-linux>. | |
68dc0745 | 640 | |
87275199 GS |
641 | Macintosh Perl programs will have the appropriate Creator and |
642 | Type, so that double-clicking them will invoke the Perl application. | |
68dc0745 | 643 | |
644 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just | |
645 | throw the perl interpreter into your cgi-bin directory, in order to | |
87275199 | 646 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 | 647 | security risk. Take the time to figure out how to do it correctly. |
648 | ||
87275199 | 649 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 | 650 | |
651 | Yes. Read L<perlrun> for more information. Some examples follow. | |
652 | (These assume standard Unix shell quoting rules.) | |
653 | ||
654 | # sum first and last fields | |
5a964f20 | 655 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 | 656 | |
657 | # identify text files | |
658 | perl -le 'for(@ARGV) {print if -f && -T _}' * | |
659 | ||
5a964f20 | 660 | # remove (most) comments from C program |
68dc0745 | 661 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
662 | ||
663 | # make file a month younger than today, defeating reaper daemons | |
664 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * | |
665 | ||
666 | # find first unused uid | |
667 | perl -le '$i++ while getpwuid($i); print $i' | |
668 | ||
669 | # display reasonable manpath | |
670 | echo $PATH | perl -nl -072 -e ' | |
671 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' | |
672 | ||
87275199 | 673 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 | 674 | |
87275199 | 675 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 | 676 | |
677 | The problem is usually that the command interpreters on those systems | |
678 | have rather different ideas about quoting than the Unix shells under | |
679 | which the one-liners were created. On some systems, you may have to | |
680 | change single-quotes to double ones, which you must I<NOT> do on Unix | |
681 | or Plan9 systems. You might also have to change a single % to a %%. | |
682 | ||
683 | For example: | |
684 | ||
685 | # Unix | |
686 | perl -e 'print "Hello world\n"' | |
687 | ||
46fc3d4c | 688 | # DOS, etc. |
68dc0745 | 689 | perl -e "print \"Hello world\n\"" |
690 | ||
46fc3d4c | 691 | # Mac |
68dc0745 | 692 | print "Hello world\n" |
693 | (then Run "Myscript" or Shift-Command-R) | |
694 | ||
695 | # VMS | |
696 | perl -e "print ""Hello world\n""" | |
697 | ||
a6dd486b | 698 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 | 699 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b | 700 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 | 701 | you'd probably have better luck like this: |
68dc0745 | 702 | |
703 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
704 | ||
46fc3d4c | 705 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 | 706 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c | 707 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 | 708 | characters as control characters. |
709 | ||
65acb1b1 TC |
710 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
711 | quotes', and `backticks`, may make one-liners easier to write. | |
712 | ||
92c2ed05 GS |
713 | There is no general solution to all of this. It is a mess, pure and |
714 | simple. Sucks to be away from Unix, huh? :-) | |
68dc0745 | 715 | |
716 | [Some of this answer was contributed by Kenneth Albanowski.] | |
717 | ||
718 | =head2 Where can I learn about CGI or Web programming in Perl? | |
719 | ||
720 | For modules, get the CGI or LWP modules from CPAN. For textbooks, | |
721 | see the two especially dedicated to web stuff in the question on | |
92c2ed05 GS |
722 | books. For problems and questions related to the web, like ``Why |
723 | do I get 500 Errors'' or ``Why doesn't it run from the browser right | |
724 | when it runs fine on the command line'', see these sources: | |
68dc0745 | 725 | |
5a964f20 TC |
726 | WWW Security FAQ |
727 | http://www.w3.org/Security/Faq/ | |
68dc0745 | 728 | |
5a964f20 TC |
729 | Web FAQ |
730 | http://www.boutell.com/faq/ | |
68dc0745 | 731 | |
5a964f20 | 732 | CGI FAQ |
6cecdcac | 733 | http://www.webthing.com/tutorials/cgifaq.html |
68dc0745 | 734 | |
5a964f20 TC |
735 | HTTP Spec |
736 | http://www.w3.org/pub/WWW/Protocols/HTTP/ | |
737 | ||
738 | HTML Spec | |
739 | http://www.w3.org/TR/REC-html40/ | |
740 | http://www.w3.org/pub/WWW/MarkUp/ | |
741 | ||
742 | CGI Spec | |
743 | http://www.w3.org/CGI/ | |
744 | ||
745 | CGI Security FAQ | |
746 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt | |
68dc0745 | 747 | |
68dc0745 | 748 | =head2 Where can I learn about object-oriented Perl programming? |
749 | ||
a6dd486b JB |
750 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
751 | L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out | |
752 | until the 5.004 release; you can get a copy (in pod, html, or | |
753 | postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ . | |
68dc0745 | 754 | |
755 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
756 | ||
757 | If you want to call C from Perl, start with L<perlxstut>, | |
758 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to | |
759 | call Perl from C, then read L<perlembed>, L<perlcall>, and | |
760 | L<perlguts>. Don't forget that you can learn a lot from looking at | |
761 | how the authors of existing extension modules wrote their code and | |
762 | solved their problems. | |
763 | ||
764 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in | |
a6dd486b | 765 | my C program; what am I doing wrong? |
68dc0745 | 766 | |
767 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If | |
768 | the tests pass, read the pods again and again and again. If they | |
87275199 | 769 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 | 770 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
771 | ||
772 | =head2 When I tried to run my script, I got this message. What does it | |
773 | mean? | |
774 | ||
87275199 GS |
775 | A complete list of Perl's error messages and warnings with explanatory |
776 | text can be found in L<perldiag>. You can also use the splain program | |
777 | (distributed with Perl) to explain the error messages: | |
68dc0745 | 778 | |
779 | perl program 2>diag.out | |
780 | splain [-v] [-p] diag.out | |
781 | ||
782 | or change your program to explain the messages for you: | |
783 | ||
784 | use diagnostics; | |
785 | ||
786 | or | |
787 | ||
788 | use diagnostics -verbose; | |
789 | ||
790 | =head2 What's MakeMaker? | |
791 | ||
87275199 | 792 | This module (part of the standard Perl distribution) is designed to |
68dc0745 | 793 | write a Makefile for an extension module from a Makefile.PL. For more |
794 | information, see L<ExtUtils::MakeMaker>. | |
795 | ||
796 | =head1 AUTHOR AND COPYRIGHT | |
797 | ||
65acb1b1 | 798 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 TC |
799 | All rights reserved. |
800 | ||
c8db1d39 | 801 | When included as an integrated part of the Standard Distribution |
d92eb7b0 GS |
802 | of Perl or of its documentation (printed or otherwise), this works is |
803 | covered under Perl's Artistic License. For separate distributions of | |
c8db1d39 TC |
804 | all or part of this FAQ outside of that, see L<perlfaq>. |
805 | ||
87275199 | 806 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
807 | domain. You are permitted and encouraged to use this code and any |
808 | derivatives thereof in your own programs for fun or for profit as you | |
809 | see fit. A simple comment in the code giving credit to the FAQ would | |
810 | be courteous but is not required. |