Commit | Line | Data |
68dc0745 |
1 | =head1 NAME |
2 | |
65acb1b1 |
3 | perlfaq3 - Programming Tools ($Revision: 1.33 $, $Date: 1998/12/29 20:12:12 $) |
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 |
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 |
5a964f20 |
22 | Regexps 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 | |
46fc3d4c |
28 | L<perltoc> provides a crude table of contents for the perl man page set. |
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 | |
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 | |
92c2ed05 |
51 | Have you used C<-w>? It enables warnings for dubious practices. |
68dc0745 |
52 | |
92c2ed05 |
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>. |
68dc0745 |
57 | |
92c2ed05 |
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. |
68dc0745 |
61 | |
92c2ed05 |
62 | open(FH, "> /etc/cantwrite") |
63 | or die "Couldn't write to /etc/cantwrite: $!\n"; |
68dc0745 |
64 | |
92c2ed05 |
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. |
68dc0745 |
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 | |
92c2ed05 |
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 | |
65acb1b1 |
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 | |
68dc0745 |
109 | =head2 How do I cross-reference my Perl programs? |
110 | |
111 | The B::Xref module, shipped with the new, alpha-release Perl compiler |
5a964f20 |
112 | (not the general distribution prior to the 5.005 release), can be used |
113 | to generate cross-reference reports for Perl programs. |
68dc0745 |
114 | |
c8db1d39 |
115 | perl -MO=Xref[,OPTIONS] scriptname.plx |
68dc0745 |
116 | |
117 | =head2 Is there a pretty-printer (formatter) for Perl? |
118 | |
92c2ed05 |
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 |
68dc0745 |
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 |
92c2ed05 |
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 |
65acb1b1 |
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 |
92c2ed05 |
141 | |
65acb1b1 |
142 | If you are used to using the I<vgrind> program for printing out nice code |
92c2ed05 |
143 | to a laser printer, you can take a stab at this using |
68dc0745 |
144 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
145 | results are not particularly satisfying for sophisticated code. |
146 | |
65acb1b1 |
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 | |
01e22528 |
150 | =head2 Is there a etags/ctags for perl? |
68dc0745 |
151 | |
01e22528 |
152 | With respect to the source code for the Perl interpreter, yes. |
153 | There has been support for etags in the source for a long time. |
154 | Ctags was introduced in v5.005_54 (and probably 5.005_03). |
155 | After building perl, type 'make etags' or 'make ctags' and both |
156 | sets of tag files will be built. |
157 | |
158 | Now, if you're looking to build a tag file for perl code, then there's |
159 | a simple one at |
68dc0745 |
160 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
65acb1b1 |
161 | the trick. And if not, it's easy to hack into what you want. |
162 | |
163 | =head2 Is there an IDE or Windows Perl Editor? |
164 | |
165 | If you're on Unix, you already have an IDE -- Unix itself. |
166 | You just have to learn the toolbox. If you're not, then you |
167 | probably don't have a toolbox, so may need something else. |
168 | |
169 | PerlBuilder (XXX URL to follow) is an integrated development |
170 | environment for Windows that supports Perl development. Perl programs |
171 | are just plain text, though, so you could download emacs for Windows |
172 | (XXX) or vim for win32 (http://www.cs.vu.nl/~tmgil/vi.html). If |
173 | you're transferring Windows files to Unix, be sure to transfer in |
174 | ASCII mode so the ends of lines are appropriately converted. |
68dc0745 |
175 | |
176 | =head2 Where can I get Perl macros for vi? |
177 | |
178 | For a complete version of Tom Christiansen's vi configuration file, |
65acb1b1 |
179 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz, |
5a964f20 |
180 | the standard benchmark file for vi emulators. This runs best with nvi, |
181 | the current version of vi out of Berkeley, which incidentally can be built |
182 | with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc. |
68dc0745 |
183 | |
184 | =head2 Where can I get perl-mode for emacs? |
185 | |
186 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
187 | perl-mode.el and support for the perl debugger built in. These should |
188 | come with the standard Emacs 19 distribution. |
189 | |
190 | In the perl source directory, you'll find a directory called "emacs", |
191 | which contains a cperl-mode that color-codes keywords, provides |
192 | context-sensitive help, and other nifty things. |
193 | |
92c2ed05 |
194 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
68dc0745 |
195 | (single quote), and mess up the indentation and hilighting. You |
65acb1b1 |
196 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 |
197 | shouldn't be an issue. |
68dc0745 |
198 | |
199 | =head2 How can I use curses with Perl? |
200 | |
201 | The Curses module from CPAN provides a dynamically loadable object |
5a964f20 |
202 | module interface to a curses library. A small demo can be found at the |
203 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; |
204 | this program repeats a command and updates the screen as needed, rendering |
205 | B<rep ps axu> similar to B<top>. |
68dc0745 |
206 | |
207 | =head2 How can I use X or Tk with Perl? |
208 | |
5a964f20 |
209 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
210 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
211 | to the Athena Widget set. Both are available from CPAN. See the |
212 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ |
68dc0745 |
213 | |
92c2ed05 |
214 | Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at |
215 | http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
216 | Guide available at |
217 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the |
218 | online manpages at |
219 | http://www-users.cs.umn.edu/~amundson/perl/perltk/toc.html . |
220 | |
68dc0745 |
221 | =head2 How can I generate simple menus without using CGI or Tk? |
222 | |
223 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz |
224 | module, which is curses-based, can help with this. |
225 | |
68dc0745 |
226 | =head2 What is undump? |
227 | |
228 | See the next questions. |
229 | |
230 | =head2 How can I make my Perl program run faster? |
231 | |
92c2ed05 |
232 | The best way to do this is to come up with a better algorithm. This |
233 | can often make a dramatic difference. Chapter 8 in the Camel has some |
234 | efficiency tips in it you might want to look at. Jon Bentley's book |
235 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
236 | on optimization, too. Advice on benchmarking boils down to: benchmark |
237 | and profile to make sure you're optimizing the right part, look for |
238 | better algorithms instead of microtuning your code, and when all else |
239 | fails consider just buying faster hardware. |
68dc0745 |
240 | |
92c2ed05 |
241 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 |
242 | AutoSplit and AutoLoader modules in the standard distribution for |
243 | that. Or you could locate the bottleneck and think about writing just |
244 | that part in C, the way we used to take bottlenecks in C code and |
245 | write them in assembler. Similar to rewriting in C is the use of |
246 | modules that have critical sections written in C (for instance, the |
247 | PDL module from CPAN). |
248 | |
249 | In some cases, it may be worth it to use the backend compiler to |
250 | produce byte code (saving compilation time) or compile into C, which |
251 | will certainly save compilation time and sometimes a small amount (but |
252 | not much) execution time. See the question about compiling your Perl |
92c2ed05 |
253 | programs for more on the compiler--the wins aren't as obvious as you'd |
254 | hope. |
68dc0745 |
255 | |
92c2ed05 |
256 | If you're currently linking your perl executable to a shared I<libc.so>, |
68dc0745 |
257 | you can often gain a 10-25% performance benefit by rebuilding it to |
258 | link with a static libc.a instead. This will make a bigger perl |
259 | executable, but your Perl programs (and programmers) may thank you for |
260 | it. See the F<INSTALL> file in the source distribution for more |
261 | information. |
262 | |
263 | Unsubstantiated reports allege that Perl interpreters that use sfio |
264 | outperform those that don't (for IO intensive applications). To try |
265 | this, see the F<INSTALL> file in the source distribution, especially |
92c2ed05 |
266 | the ``Selecting File IO mechanisms'' section. |
68dc0745 |
267 | |
268 | The undump program was an old attempt to speed up your Perl program |
269 | by storing the already-compiled form to disk. This is no longer |
270 | a viable option, as it only worked on a few architectures, and |
271 | wasn't a good solution anyway. |
272 | |
273 | =head2 How can I make my Perl program take less memory? |
274 | |
275 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
276 | throw memory at a problem. Scalars in Perl use more memory than |
65acb1b1 |
277 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 |
278 | there's still a lot to be done, recent releases have been addressing |
279 | these issues. For example, as of 5.004, duplicate hash keys are |
280 | shared amongst all hashes using them, so require no reallocation. |
281 | |
282 | In some cases, using substr() or vec() to simulate arrays can be |
283 | highly beneficial. For example, an array of a thousand booleans will |
284 | take at least 20,000 bytes of space, but it can be turned into one |
285 | 125-byte bit vector for a considerable memory savings. The standard |
286 | Tie::SubstrHash module can also help for certain types of data |
287 | structure. If you're working with specialist data structures |
288 | (matrices, for instance) modules that implement these in C may use |
289 | less memory than equivalent Perl modules. |
290 | |
291 | Another thing to try is learning whether your Perl was compiled with |
54310121 |
292 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 |
293 | is, try using the other one and see whether this makes a difference. |
294 | Information about malloc is in the F<INSTALL> file in the source |
295 | distribution. You can find out whether you are using perl's malloc by |
296 | typing C<perl -V:usemymalloc>. |
297 | |
298 | =head2 Is it unsafe to return a pointer to local data? |
299 | |
300 | No, Perl's garbage collection system takes care of this. |
301 | |
302 | sub makeone { |
303 | my @a = ( 1 .. 10 ); |
304 | return \@a; |
305 | } |
306 | |
307 | for $i ( 1 .. 10 ) { |
308 | push @many, makeone(); |
309 | } |
310 | |
311 | print $many[4][5], "\n"; |
312 | |
313 | print "@many\n"; |
314 | |
315 | =head2 How can I free an array or hash so my program shrinks? |
316 | |
c8db1d39 |
317 | You can't. On most operating systems, memory allocated to a program |
318 | can never be returned to the system. That's why long-running programs |
65acb1b1 |
319 | sometimes re-exec themselves. Some operating systems (notably, |
320 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no |
321 | longer used, but it doesn't appear to happen with Perl (yet). The Mac |
322 | appears to be the only platform that will reliably (albeit, slowly) |
323 | return memory to the OS. |
324 | |
325 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef |
326 | $scalar> will return memory to the system, while on Solaris 2.6 it |
327 | won't. In general, try it yourself and see. |
68dc0745 |
328 | |
329 | However, judicious use of my() on your variables will help make sure |
330 | that they go out of scope so that Perl can free up their storage for |
92c2ed05 |
331 | use in other parts of your program. A global variable, of course, never |
68dc0745 |
332 | goes out of scope, so you can't get its space automatically reclaimed, |
333 | although undef()ing and/or delete()ing it will achieve the same effect. |
46fc3d4c |
334 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 |
335 | or should be worrying about much in Perl, but even this capability |
336 | (preallocation of data types) is in the works. |
337 | |
338 | =head2 How can I make my CGI script more efficient? |
339 | |
340 | Beyond the normal measures described to make general Perl programs |
341 | faster or smaller, a CGI program has additional issues. It may be run |
342 | several times per second. Given that each time it runs it will need |
46fc3d4c |
343 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 |
344 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c |
345 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 |
346 | |
92c2ed05 |
347 | There are two popular ways to avoid this overhead. One solution |
348 | involves running the Apache HTTP server (available from |
68dc0745 |
349 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
92c2ed05 |
350 | plugin modules. |
351 | |
352 | With mod_perl and the Apache::Registry module (distributed with |
353 | mod_perl), httpd will run with an embedded Perl interpreter which |
354 | pre-compiles your script and then executes it within the same address |
355 | space without forking. The Apache extension also gives Perl access to |
356 | the internal server API, so modules written in Perl can do just about |
357 | anything a module written in C can. For more on mod_perl, see |
358 | http://perl.apache.org/ |
359 | |
65acb1b1 |
360 | With the FCGI module (from CPAN) and the mod_fastcgi |
92c2ed05 |
361 | module (available from http://www.fastcgi.com/) each of your perl |
362 | scripts becomes a permanent CGI daemon process. |
68dc0745 |
363 | |
364 | Both of these solutions can have far-reaching effects on your system |
365 | and on the way you write your CGI scripts, so investigate them with |
366 | care. |
367 | |
92c2ed05 |
368 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 |
369 | |
65acb1b1 |
370 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
c8db1d39 |
371 | (http://www.binevolve.com/ or http://www.binevolve.com/bine/vep) might |
372 | also be worth looking at. It will allow you to increase the performance |
92c2ed05 |
373 | of your perl scripts, upto 25 times faster than normal CGI perl by |
c8db1d39 |
374 | running in persistent perl mode, or 4 to 5 times faster without any |
92c2ed05 |
375 | modification to your existing CGI scripts. Fully functional evaluation |
c8db1d39 |
376 | copies are available from the web site. |
377 | |
68dc0745 |
378 | =head2 How can I hide the source for my Perl program? |
379 | |
380 | Delete it. :-) Seriously, there are a number of (mostly |
92c2ed05 |
381 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 |
382 | |
383 | First of all, however, you I<can't> take away read permission, because |
384 | the source code has to be readable in order to be compiled and |
385 | interpreted. (That doesn't mean that a CGI script's source is |
92c2ed05 |
386 | readable by people on the web, though, only by people with access to |
387 | the filesystem) So you have to leave the permissions at the socially |
388 | friendly 0755 level. |
68dc0745 |
389 | |
390 | Some people regard this as a security problem. If your program does |
391 | insecure things, and relies on people not knowing how to exploit those |
392 | insecurities, it is not secure. It is often possible for someone to |
393 | determine the insecure things and exploit them without viewing the |
394 | source. Security through obscurity, the name for hiding your bugs |
395 | instead of fixing them, is little security indeed. |
396 | |
92c2ed05 |
397 | You can try using encryption via source filters (Filter::* from CPAN), |
65acb1b1 |
398 | but any decent programmer will be able to decrypt it. You can try using |
399 | the byte code compiler and interpreter described below, but the curious |
400 | might still be able to de-compile it. You can try using the native-code |
401 | compiler described below, but crackers might be able to disassemble it. |
402 | These pose varying degrees of difficulty to people wanting to get at |
403 | your code, but none can definitively conceal it (this is true of every |
68dc0745 |
404 | language, not just Perl). |
405 | |
406 | If you're concerned about people profiting from your code, then the |
407 | bottom line is that nothing but a restrictive licence will give you |
408 | legal security. License your software and pepper it with threatening |
92c2ed05 |
409 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 |
410 | Your access to it does not give you permission to use it blah blah |
92c2ed05 |
411 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
68dc0745 |
412 | you want to be sure your licence's wording will stand up in court. |
413 | |
54310121 |
414 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 |
415 | |
416 | Malcolm Beattie has written a multifunction backend compiler, |
5e3006a4 |
417 | available from CPAN, that can do both these things. It is included |
418 | in the perl5.005 release, but is still considered experimental. |
419 | This means it's fun to play with if you're a programmer but not |
420 | really for people looking for turn-key solutions. |
68dc0745 |
421 | |
92c2ed05 |
422 | Merely compiling into C does not in and of itself guarantee that your |
423 | code will run very much faster. That's because except for lucky cases |
424 | where a lot of native type inferencing is possible, the normal Perl |
425 | run time system is still present and so your program will take just as |
426 | long to run and be just as big. Most programs save little more than |
427 | compilation time, leaving execution no more than 10-30% faster. A few |
428 | rare programs actually benefit significantly (like several times |
429 | faster), but this takes some tweaking of your code. |
68dc0745 |
430 | |
68dc0745 |
431 | You'll probably be astonished to learn that the current version of the |
432 | compiler generates a compiled form of your script whose executable is |
433 | just as big as the original perl executable, and then some. That's |
434 | because as currently written, all programs are prepared for a full |
435 | eval() statement. You can tremendously reduce this cost by building a |
92c2ed05 |
436 | shared I<libperl.so> library and linking against that. See the |
68dc0745 |
437 | F<INSTALL> podfile in the perl source distribution for details. If |
438 | you link your main perl binary with this, it will make it miniscule. |
92c2ed05 |
439 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 |
440 | size! |
441 | |
5a964f20 |
442 | In general, the compiler will do nothing to make a Perl program smaller, |
443 | faster, more portable, or more secure. In fact, it will usually hurt |
444 | all of those. The executable will be bigger, your VM system may take |
445 | longer to load the whole thing, the binary is fragile and hard to fix, |
446 | and compilation never stopped software piracy in the form of crackers, |
447 | viruses, or bootleggers. The real advantage of the compiler is merely |
448 | packaging, and once you see the size of what it makes (well, unless |
449 | you use a shared I<libperl.so>), you'll probably want a complete |
5e3006a4 |
450 | Perl install anyway. |
5a964f20 |
451 | |
65acb1b1 |
452 | =head2 How can I compile Perl into Java? |
453 | |
454 | You can't. Not yet, anyway. You can integrate Java and Perl with the |
455 | Perl Resource Kit from O'Reilly and Associates. See |
456 | http://www.oreilly.com/catalog/prkunix/ for more information. |
457 | The Java interface will be supported in the core 5.006 release |
458 | of Perl. |
459 | |
92c2ed05 |
460 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 |
461 | |
462 | For OS/2 just use |
463 | |
464 | extproc perl -S -your_switches |
465 | |
466 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
46fc3d4c |
467 | `extproc' handling). For DOS one should first invent a corresponding |
68dc0745 |
468 | batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the |
469 | F<INSTALL> file in the source distribution for more information). |
470 | |
92c2ed05 |
471 | The Win95/NT installation, when using the ActiveState port of Perl, |
472 | will modify the Registry to associate the C<.pl> extension with the |
65acb1b1 |
473 | perl interpreter. If you install another port (Gurusamy Sarathy's is |
474 | the recommended Win95/NT port), or (eventually) build your own |
475 | Win95/NT Perl using a Windows port of gcc (e.g., with cygwin32 or |
476 | mingw32), then you'll have to modify the Registry yourself. In |
477 | addition to associating C<.pl> with the interpreter, NT people can |
478 | use: C<SET PATHEXT=%PATHEXT%;.PL> to let them run the program |
479 | C<install-linux.pl> merely by typing C<install-linux>. |
68dc0745 |
480 | |
368c9434 |
481 | Macintosh perl scripts will have the appropriate Creator and |
68dc0745 |
482 | Type, so that double-clicking them will invoke the perl application. |
483 | |
484 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
485 | throw the perl interpreter into your cgi-bin directory, in order to |
486 | get your scripts working for a web server. This is an EXTREMELY big |
487 | security risk. Take the time to figure out how to do it correctly. |
488 | |
489 | =head2 Can I write useful perl programs on the command line? |
490 | |
491 | Yes. Read L<perlrun> for more information. Some examples follow. |
492 | (These assume standard Unix shell quoting rules.) |
493 | |
494 | # sum first and last fields |
5a964f20 |
495 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 |
496 | |
497 | # identify text files |
498 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
499 | |
5a964f20 |
500 | # remove (most) comments from C program |
68dc0745 |
501 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
502 | |
503 | # make file a month younger than today, defeating reaper daemons |
504 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
505 | |
506 | # find first unused uid |
507 | perl -le '$i++ while getpwuid($i); print $i' |
508 | |
509 | # display reasonable manpath |
510 | echo $PATH | perl -nl -072 -e ' |
511 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
512 | |
513 | Ok, the last one was actually an obfuscated perl entry. :-) |
514 | |
46fc3d4c |
515 | =head2 Why don't perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 |
516 | |
517 | The problem is usually that the command interpreters on those systems |
518 | have rather different ideas about quoting than the Unix shells under |
519 | which the one-liners were created. On some systems, you may have to |
520 | change single-quotes to double ones, which you must I<NOT> do on Unix |
521 | or Plan9 systems. You might also have to change a single % to a %%. |
522 | |
523 | For example: |
524 | |
525 | # Unix |
526 | perl -e 'print "Hello world\n"' |
527 | |
46fc3d4c |
528 | # DOS, etc. |
68dc0745 |
529 | perl -e "print \"Hello world\n\"" |
530 | |
46fc3d4c |
531 | # Mac |
68dc0745 |
532 | print "Hello world\n" |
533 | (then Run "Myscript" or Shift-Command-R) |
534 | |
535 | # VMS |
536 | perl -e "print ""Hello world\n""" |
537 | |
92c2ed05 |
538 | The problem is that none of this is reliable: it depends on the |
539 | command interpreter. Under Unix, the first two often work. Under DOS, |
540 | it's entirely possible neither works. If 4DOS was the command shell, |
541 | you'd probably have better luck like this: |
68dc0745 |
542 | |
543 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
544 | |
46fc3d4c |
545 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 |
546 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c |
547 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 |
548 | characters as control characters. |
549 | |
65acb1b1 |
550 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
551 | quotes', and `backticks`, may make one-liners easier to write. |
552 | |
92c2ed05 |
553 | There is no general solution to all of this. It is a mess, pure and |
554 | simple. Sucks to be away from Unix, huh? :-) |
68dc0745 |
555 | |
556 | [Some of this answer was contributed by Kenneth Albanowski.] |
557 | |
558 | =head2 Where can I learn about CGI or Web programming in Perl? |
559 | |
560 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
561 | see the two especially dedicated to web stuff in the question on |
92c2ed05 |
562 | books. For problems and questions related to the web, like ``Why |
563 | do I get 500 Errors'' or ``Why doesn't it run from the browser right |
564 | when it runs fine on the command line'', see these sources: |
68dc0745 |
565 | |
5a964f20 |
566 | WWW Security FAQ |
567 | http://www.w3.org/Security/Faq/ |
68dc0745 |
568 | |
5a964f20 |
569 | Web FAQ |
570 | http://www.boutell.com/faq/ |
68dc0745 |
571 | |
5a964f20 |
572 | CGI FAQ |
573 | http://www.webthing.com/page.cgi/cgifaq |
68dc0745 |
574 | |
5a964f20 |
575 | HTTP Spec |
576 | http://www.w3.org/pub/WWW/Protocols/HTTP/ |
577 | |
578 | HTML Spec |
579 | http://www.w3.org/TR/REC-html40/ |
580 | http://www.w3.org/pub/WWW/MarkUp/ |
581 | |
582 | CGI Spec |
583 | http://www.w3.org/CGI/ |
584 | |
585 | CGI Security FAQ |
586 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt |
68dc0745 |
587 | |
68dc0745 |
588 | |
589 | =head2 Where can I learn about object-oriented Perl programming? |
590 | |
591 | L<perltoot> is a good place to start, and you can use L<perlobj> and |
592 | L<perlbot> for reference. Perltoot didn't come out until the 5.004 |
593 | release, but you can get a copy (in pod, html, or postscript) from |
594 | http://www.perl.com/CPAN/doc/FMTEYEWTK/ . |
595 | |
596 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] |
597 | |
598 | If you want to call C from Perl, start with L<perlxstut>, |
599 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
600 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
601 | L<perlguts>. Don't forget that you can learn a lot from looking at |
602 | how the authors of existing extension modules wrote their code and |
603 | solved their problems. |
604 | |
605 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in |
606 | my C program, what am I doing wrong? |
607 | |
608 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
609 | the tests pass, read the pods again and again and again. If they |
46fc3d4c |
610 | fail, see L<perlbug> and send a bugreport with the output of |
68dc0745 |
611 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
612 | |
613 | =head2 When I tried to run my script, I got this message. What does it |
614 | mean? |
615 | |
616 | L<perldiag> has a complete list of perl's error messages and warnings, |
617 | with explanatory text. You can also use the splain program (distributed |
618 | with perl) to explain the error messages: |
619 | |
620 | perl program 2>diag.out |
621 | splain [-v] [-p] diag.out |
622 | |
623 | or change your program to explain the messages for you: |
624 | |
625 | use diagnostics; |
626 | |
627 | or |
628 | |
629 | use diagnostics -verbose; |
630 | |
631 | =head2 What's MakeMaker? |
632 | |
633 | This module (part of the standard perl distribution) is designed to |
634 | write a Makefile for an extension module from a Makefile.PL. For more |
635 | information, see L<ExtUtils::MakeMaker>. |
636 | |
637 | =head1 AUTHOR AND COPYRIGHT |
638 | |
65acb1b1 |
639 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 |
640 | All rights reserved. |
641 | |
c8db1d39 |
642 | When included as an integrated part of the Standard Distribution |
643 | of Perl or of its documentation (printed or otherwise), this works is |
644 | covered under Perl's Artistic Licence. For separate distributions of |
645 | all or part of this FAQ outside of that, see L<perlfaq>. |
646 | |
647 | Irrespective of its distribution, all code examples here are public |
648 | domain. You are permitted and encouraged to use this code and any |
649 | derivatives thereof in your own programs for fun or for profit as you |
650 | see fit. A simple comment in the code giving credit to the FAQ would |
651 | be courteous but is not required. |
65acb1b1 |
652 | |