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