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 manpages? 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 manpage 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) manpage, 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 (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
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 Perl programs are just plain text, so any editor will do.
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.
166 If you want an IDE, check the following:
172 ActiveState's cross-platform (as of April 2001 Windows and Linux),
173 multi-language IDE has Perl support, including a regular expression
174 debugger and remote debugging
175 (http://www.ActiveState.com/Products/Komodo/index.html). (Visual
176 Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta
177 (http://www.ActiveState.com/Products/VisualPerl/index.html)).
179 =item The Object System
181 (http://www.castlelink.co.uk/object_system/) is a Perl web
182 applications development IDE, apparently for any platform
187 ( http://open-perl-ide.sourceforge.net/ )
188 Open Perl IDE is an integrated development environment for writing
189 and debugging Perl scripts with ActiveState's ActivePerl distribution
190 under Windows 95/98/NT/2000.
194 (http://www.solutionsoft.com/perl.htm) is an integrated development
195 environment for Windows that supports Perl development.
199 ( http://helpconsulting.net/visiperl/ )
200 From Help Consulting, for Windows.
204 For Windows there's also the
210 ( http://www.codemagiccd.com/ ) Collection of various programming
211 tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming
212 tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP
213 GNU C/C++ compiler, Cint C interpreter, YaBasic.
217 For editors: if you're on Unix you probably have vi or a vi clone already,
218 and possibly an emacs too, so you may not need to download anything.
219 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
220 best available Perl editing mode in any editor.
222 For Windows editors: you can download an Emacs
228 http://www.gnu.org/software/emacs/windows/ntemacs.html
232 http://members.nbci.com/uemacs/
236 http://www.xemacs.org/Download/index.html
240 or a vi clone such as
246 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
256 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
260 For vi lovers in general, Windows or elsewhere:
261 http://www.thomer.com/thomer/vi/vi.html.
263 nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
264 yet another vi clone, unfortunately not available for Windows, but in
265 UNIX platforms you might be interested in trying it out, firstly because
266 strictly speaking it is not a vi clone, it is the real vi, or the new
267 incarnation of it, and secondly because you can embed Perl inside it
268 to use Perl as the scripting language. nvi is not alone in this,
269 though: at least also vim and vile offer an embedded Perl.
271 The following are Win32 multilanguage editor/IDESs that support Perl:
277 http://www.starbase.com/
281 http://www.MultiEdit.com/
285 http://www.slickedit.com/
289 There is also a toyedit Text widget based editor written in Perl
290 that is distributed with the Tk module on CPAN. The ptkdb
291 (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
292 acts as a development environment of sorts. Perl Composer
293 (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
296 In addition to an editor/IDE you might be interested in a more
297 powerful shell environment for Win32. Your options include
303 from the Cygwin package (http://sources.redhat.com/cygwin/)
307 from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
308 the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
312 ftp://ftp.astron.com/pub/tcsh/, see also
313 http://www.primate.wisc.edu/software/csh-tcsh-book/
317 ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
321 MKS and U/WIN are commercial (U/WIN is free for educational and
322 research purposes), Cygwin is covered by the GNU Public License (but
323 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
324 contain (in addition to the shells) a comprehensive set of standard
325 UNIX toolkit utilities.
327 If you're transferring text files between Unix and Windows using FTP
328 be sure to transfer them in ASCII mode so the ends of lines are
329 appropriately converted.
331 On Mac OS the MacPerl Application comes with a simple 32k text editor
332 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
333 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
338 =item BBEdit and BBEdit Lite
340 are text editors for Mac OS that have a Perl sensitivity mode
341 (http://web.barebones.com/).
345 is an editor, written and extensible in Tcl, that nonetheless has
346 built in support for several popular markup and programming languages
347 including Perl and HTML (http://alpha.olm.net/).
351 Pepper and Pe are programming language sensitive text editors for Mac
352 OS X and BeOS respectively (http://www.hekkelman.com/).
354 =head2 Where can I get Perl macros for vi?
356 For a complete version of Tom Christiansen's vi configuration file,
357 see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
358 the standard benchmark file for vi emulators. The file runs best with nvi,
359 the current version of vi out of Berkeley, which incidentally can be built
360 with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.
362 =head2 Where can I get perl-mode for emacs?
364 Since Emacs version 19 patchlevel 22 or so, there have been both a
365 perl-mode.el and support for the Perl debugger built in. These should
366 come with the standard Emacs 19 distribution.
368 In the Perl source directory, you'll find a directory called "emacs",
369 which contains a cperl-mode that color-codes keywords, provides
370 context-sensitive help, and other nifty things.
372 Note that the perl-mode of emacs will have fits with C<"main'foo">
373 (single quote), and mess up the indentation and highlighting. You
374 are probably using C<"main::foo"> in new Perl code anyway, so this
375 shouldn't be an issue.
377 =head2 How can I use curses with Perl?
379 The Curses module from CPAN provides a dynamically loadable object
380 module interface to a curses library. A small demo can be found at the
381 directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
382 this program repeats a command and updates the screen as needed, rendering
383 B<rep ps axu> similar to B<top>.
385 =head2 How can I use X or Tk with Perl?
387 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
388 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
389 to the Athena Widget set. Both are available from CPAN. See the
390 directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
392 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
393 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
395 http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
397 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
399 =head2 How can I generate simple menus without using CGI or Tk?
401 The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
402 module, which is curses-based, can help with this.
404 =head2 What is undump?
406 See the next question on ``How can I make my Perl program run faster?''
408 =head2 How can I make my Perl program run faster?
410 The best way to do this is to come up with a better algorithm. This
411 can often make a dramatic difference. Jon Bentley's book
412 ``Programming Pearls'' (that's not a misspelling!) has some good tips
413 on optimization, too. Advice on benchmarking boils down to: benchmark
414 and profile to make sure you're optimizing the right part, look for
415 better algorithms instead of microtuning your code, and when all else
416 fails consider just buying faster hardware. You will probably want to
417 read the answer to the earlier question ``How do I profile my Perl programs?''
418 if you haven't done so already.
420 A different approach is to autoload seldom-used Perl code. See the
421 AutoSplit and AutoLoader modules in the standard distribution for
422 that. Or you could locate the bottleneck and think about writing just
423 that part in C, the way we used to take bottlenecks in C code and
424 write them in assembler. Similar to rewriting in C,
425 modules that have critical sections can be written in C (for instance, the
426 PDL module from CPAN).
428 In some cases, it may be worth it to use the backend compiler to
429 produce byte code (saving compilation time) or compile into C, which
430 will certainly save compilation time and sometimes a small amount (but
431 not much) execution time. See the question about compiling your Perl
432 programs for more on the compiler--the wins aren't as obvious as you'd
435 If you're currently linking your perl executable to a shared I<libc.so>,
436 you can often gain a 10-25% performance benefit by rebuilding it to
437 link with a static libc.a instead. This will make a bigger perl
438 executable, but your Perl programs (and programmers) may thank you for
439 it. See the F<INSTALL> file in the source distribution for more
442 Unsubstantiated reports allege that Perl interpreters that use sfio
443 outperform those that don't (for I/O intensive applications). To try
444 this, see the F<INSTALL> file in the source distribution, especially
445 the ``Selecting File I/O mechanisms'' section.
447 The undump program was an old attempt to speed up your Perl program
448 by storing the already-compiled form to disk. This is no longer
449 a viable option, as it only worked on a few architectures, and
450 wasn't a good solution anyway.
452 =head2 How can I make my Perl program take less memory?
454 When it comes to time-space tradeoffs, Perl nearly always prefers to
455 throw memory at a problem. Scalars in Perl use more memory than
456 strings in C, arrays take more than that, and hashes use even more. While
457 there's still a lot to be done, recent releases have been addressing
458 these issues. For example, as of 5.004, duplicate hash keys are
459 shared amongst all hashes using them, so require no reallocation.
461 In some cases, using substr() or vec() to simulate arrays can be
462 highly beneficial. For example, an array of a thousand booleans will
463 take at least 20,000 bytes of space, but it can be turned into one
464 125-byte bit vector--a considerable memory savings. The standard
465 Tie::SubstrHash module can also help for certain types of data
466 structure. If you're working with specialist data structures
467 (matrices, for instance) modules that implement these in C may use
468 less memory than equivalent Perl modules.
470 Another thing to try is learning whether your Perl was compiled with
471 the system malloc or with Perl's builtin malloc. Whichever one it
472 is, try using the other one and see whether this makes a difference.
473 Information about malloc is in the F<INSTALL> file in the source
474 distribution. You can find out whether you are using perl's malloc by
475 typing C<perl -V:usemymalloc>.
477 =head2 Is it unsafe to return a pointer to local data?
479 No, Perl's garbage collection system takes care of this.
487 push @many, makeone();
490 print $many[4][5], "\n";
494 =head2 How can I free an array or hash so my program shrinks?
496 You can't. On most operating systems, memory allocated to a program
497 can never be returned to the system. That's why long-running programs
498 sometimes re-exec themselves. Some operating systems (notably,
499 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
500 longer used, but it doesn't appear to happen with Perl (yet). The Mac
501 appears to be the only platform that will reliably (albeit, slowly)
502 return memory to the OS.
504 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
505 $scalar> will return memory to the system, while on Solaris 2.6 it
506 won't. In general, try it yourself and see.
508 However, judicious use of my() on your variables will help make sure
509 that they go out of scope so that Perl can free up that space for
510 use in other parts of your program. A global variable, of course, never
511 goes out of scope, so you can't get its space automatically reclaimed,
512 although undef()ing and/or delete()ing it will achieve the same effect.
513 In general, memory allocation and de-allocation isn't something you can
514 or should be worrying about much in Perl, but even this capability
515 (preallocation of data types) is in the works.
517 =head2 How can I make my CGI script more efficient?
519 Beyond the normal measures described to make general Perl programs
520 faster or smaller, a CGI program has additional issues. It may be run
521 several times per second. Given that each time it runs it will need
522 to be re-compiled and will often allocate a megabyte or more of system
523 memory, this can be a killer. Compiling into C B<isn't going to help
524 you> because the process start-up overhead is where the bottleneck is.
526 There are two popular ways to avoid this overhead. One solution
527 involves running the Apache HTTP server (available from
528 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
531 With mod_perl and the Apache::Registry module (distributed with
532 mod_perl), httpd will run with an embedded Perl interpreter which
533 pre-compiles your script and then executes it within the same address
534 space without forking. The Apache extension also gives Perl access to
535 the internal server API, so modules written in Perl can do just about
536 anything a module written in C can. For more on mod_perl, see
537 http://perl.apache.org/
539 With the FCGI module (from CPAN) and the mod_fastcgi
540 module (available from http://www.fastcgi.com/) each of your Perl
541 programs becomes a permanent CGI daemon process.
543 Both of these solutions can have far-reaching effects on your system
544 and on the way you write your CGI programs, so investigate them with
547 See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
549 A non-free, commercial product, ``The Velocity Engine for Perl'',
550 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
551 might also be worth looking at. It will allow you to increase the
552 performance of your Perl programs, running programs up to 25 times
553 faster than normal CGI Perl when running in persistent Perl mode or 4
554 to 5 times faster without any modification to your existing CGI
555 programs. Fully functional evaluation copies are available from the
558 =head2 How can I hide the source for my Perl program?
560 Delete it. :-) Seriously, there are a number of (mostly
561 unsatisfactory) solutions with varying levels of ``security''.
563 First of all, however, you I<can't> take away read permission, because
564 the source code has to be readable in order to be compiled and
565 interpreted. (That doesn't mean that a CGI script's source is
566 readable by people on the web, though--only by people with access to
567 the filesystem.) So you have to leave the permissions at the socially
570 Some people regard this as a security problem. If your program does
571 insecure things and relies on people not knowing how to exploit those
572 insecurities, it is not secure. It is often possible for someone to
573 determine the insecure things and exploit them without viewing the
574 source. Security through obscurity, the name for hiding your bugs
575 instead of fixing them, is little security indeed.
577 You can try using encryption via source filters (Starting from Perl
578 5.8 the Filter::Simple and Filter::Util::Call modules are included in
579 the standard distribution), but any decent programmer will be able to
580 decrypt it. You can try using the byte code compiler and interpreter
581 described below, but the curious might still be able to de-compile it.
582 You can try using the native-code compiler described below, but
583 crackers might be able to disassemble it. These pose varying degrees
584 of difficulty to people wanting to get at your code, but none can
585 definitively conceal it (true of every language, not just Perl).
587 If you're concerned about people profiting from your code, then the
588 bottom line is that nothing but a restrictive license will give you
589 legal security. License your software and pepper it with threatening
590 statements like ``This is unpublished proprietary software of XYZ Corp.
591 Your access to it does not give you permission to use it blah blah
592 blah.'' We are not lawyers, of course, so you should see a lawyer if
593 you want to be sure your license's wording will stand up in court.
595 =head2 How can I compile my Perl program into byte code or C?
597 Malcolm Beattie has written a multifunction backend compiler,
598 available from CPAN, that can do both these things. It is included
599 in the perl5.005 release, but is still considered experimental.
600 This means it's fun to play with if you're a programmer but not
601 really for people looking for turn-key solutions.
603 Merely compiling into C does not in and of itself guarantee that your
604 code will run very much faster. That's because except for lucky cases
605 where a lot of native type inferencing is possible, the normal Perl
606 run-time system is still present and so your program will take just as
607 long to run and be just as big. Most programs save little more than
608 compilation time, leaving execution no more than 10-30% faster. A few
609 rare programs actually benefit significantly (even running several times
610 faster), but this takes some tweaking of your code.
612 You'll probably be astonished to learn that the current version of the
613 compiler generates a compiled form of your script whose executable is
614 just as big as the original perl executable, and then some. That's
615 because as currently written, all programs are prepared for a full
616 eval() statement. You can tremendously reduce this cost by building a
617 shared I<libperl.so> library and linking against that. See the
618 F<INSTALL> podfile in the Perl source distribution for details. If
619 you link your main perl binary with this, it will make it minuscule.
620 For example, on one author's system, F</usr/bin/perl> is only 11k in
623 In general, the compiler will do nothing to make a Perl program smaller,
624 faster, more portable, or more secure. In fact, it can make your
625 situation worse. The executable will be bigger, your VM system may take
626 longer to load the whole thing, the binary is fragile and hard to fix,
627 and compilation never stopped software piracy in the form of crackers,
628 viruses, or bootleggers. The real advantage of the compiler is merely
629 packaging, and once you see the size of what it makes (well, unless
630 you use a shared I<libperl.so>), you'll probably want a complete
633 =head2 How can I compile Perl into Java?
635 You can also integrate Java and Perl with the
636 Perl Resource Kit from O'Reilly and Associates. See
637 http://www.oreilly.com/catalog/prkunix/ .
639 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
640 development, allows Perl code to be called from Java. See jpl/README
641 in the Perl source tree.
643 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
647 extproc perl -S -your_switches
649 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
650 `extproc' handling). For DOS one should first invent a corresponding
651 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
652 F<INSTALL> file in the source distribution for more information).
654 The Win95/NT installation, when using the ActiveState port of Perl,
655 will modify the Registry to associate the C<.pl> extension with the
656 perl interpreter. If you install another port, perhaps even building
657 your own Win95/NT Perl from the standard sources by using a Windows port
658 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
659 the Registry yourself. In addition to associating C<.pl> with the
660 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
661 run the program C<install-linux.pl> merely by typing C<install-linux>.
663 Macintosh Perl programs will have the appropriate Creator and
664 Type, so that double-clicking them will invoke the Perl application.
666 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
667 throw the perl interpreter into your cgi-bin directory, in order to
668 get your programs working for a web server. This is an EXTREMELY big
669 security risk. Take the time to figure out how to do it correctly.
671 =head2 Can I write useful Perl programs on the command line?
673 Yes. Read L<perlrun> for more information. Some examples follow.
674 (These assume standard Unix shell quoting rules.)
676 # sum first and last fields
677 perl -lane 'print $F[0] + $F[-1]' *
679 # identify text files
680 perl -le 'for(@ARGV) {print if -f && -T _}' *
682 # remove (most) comments from C program
683 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
685 # make file a month younger than today, defeating reaper daemons
686 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
688 # find first unused uid
689 perl -le '$i++ while getpwuid($i); print $i'
691 # display reasonable manpath
692 echo $PATH | perl -nl -072 -e '
693 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
695 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
697 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
699 The problem is usually that the command interpreters on those systems
700 have rather different ideas about quoting than the Unix shells under
701 which the one-liners were created. On some systems, you may have to
702 change single-quotes to double ones, which you must I<NOT> do on Unix
703 or Plan9 systems. You might also have to change a single % to a %%.
708 perl -e 'print "Hello world\n"'
711 perl -e "print \"Hello world\n\""
714 print "Hello world\n"
715 (then Run "Myscript" or Shift-Command-R)
718 perl -e "print ""Hello world\n"""
720 The problem is that none of these examples are reliable: they depend on the
721 command interpreter. Under Unix, the first two often work. Under DOS,
722 it's entirely possible that neither works. If 4DOS was the command shell,
723 you'd probably have better luck like this:
725 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
727 Under the Mac, it depends which environment you are using. The MacPerl
728 shell, or MPW, is much like Unix shells in its support for several
729 quoting variants, except that it makes free use of the Mac's non-ASCII
730 characters as control characters.
732 Using qq(), q(), and qx(), instead of "double quotes", 'single
733 quotes', and `backticks`, may make one-liners easier to write.
735 There is no general solution to all of this. It is a mess, pure and
736 simple. Sucks to be away from Unix, huh? :-)
738 [Some of this answer was contributed by Kenneth Albanowski.]
740 =head2 Where can I learn about CGI or Web programming in Perl?
742 For modules, get the CGI or LWP modules from CPAN. For textbooks,
743 see the two especially dedicated to web stuff in the question on
744 books. For problems and questions related to the web, like ``Why
745 do I get 500 Errors'' or ``Why doesn't it run from the browser right
746 when it runs fine on the command line'', see these sources:
749 http://www.w3.org/Security/Faq/
752 http://www.boutell.com/faq/
755 http://www.webthing.com/tutorials/cgifaq.html
758 http://www.w3.org/pub/WWW/Protocols/HTTP/
761 http://www.w3.org/TR/REC-html40/
762 http://www.w3.org/pub/WWW/MarkUp/
765 http://www.w3.org/CGI/
768 http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
770 =head2 Where can I learn about object-oriented Perl programming?
772 A good place to start is L<perltoot>, and you can use L<perlobj>,
773 L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out
774 until the 5.004 release; you can get a copy (in pod, html, or
775 postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
777 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
779 If you want to call C from Perl, start with L<perlxstut>,
780 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
781 call Perl from C, then read L<perlembed>, L<perlcall>, and
782 L<perlguts>. Don't forget that you can learn a lot from looking at
783 how the authors of existing extension modules wrote their code and
784 solved their problems.
786 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
787 my C program; what am I doing wrong?
789 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
790 the tests pass, read the pods again and again and again. If they
791 fail, see L<perlbug> and send a bug report with the output of
792 C<make test TEST_VERBOSE=1> along with C<perl -V>.
794 =head2 When I tried to run my script, I got this message. What does it
797 A complete list of Perl's error messages and warnings with explanatory
798 text can be found in L<perldiag>. You can also use the splain program
799 (distributed with Perl) to explain the error messages:
801 perl program 2>diag.out
802 splain [-v] [-p] diag.out
804 or change your program to explain the messages for you:
810 use diagnostics -verbose;
812 =head2 What's MakeMaker?
814 This module (part of the standard Perl distribution) is designed to
815 write a Makefile for an extension module from a Makefile.PL. For more
816 information, see L<ExtUtils::MakeMaker>.
818 =head1 AUTHOR AND COPYRIGHT
820 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
823 This documentation is free; you can redistribute it and/or modify it
824 under the same terms as Perl itself.
826 Irrespective of its distribution, all code examples here are in the public
827 domain. You are permitted and encouraged to use this code and any
828 derivatives thereof in your own programs for fun or for profit as you
829 see fit. A simple comment in the code giving credit to the FAQ would
830 be courteous but is not required.