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 (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 a Windows IDE, check the following:
172 http://www.codemagiccd.com/
176 ActiveState's cross-platform, multi-language IDE has Perl support,
177 including a regular expression debugger and remote debugging
178 (http://www.ActiveState.com/Products/Komodo/index.html).
179 (Visual Perl, a Visual Studio.NET plug-in is currently (early 2001)
180 in beta (http://www.ActiveState.com/Products/VisualPerl/index.html)).
182 =item The Object System
184 (http://www.castlelink.co.uk/object_system/) is a Perl web
185 applications development IDE.
187 =item Perl code magic
189 (http://www.petes-place.com/codemagic.html).
193 http://helpconsulting.net/visiperl/, from Help Consulting.
197 For editors: if you're on Unix you probably have vi or a vi clone already,
198 and possibly an emacs too, so you may not need to download anything.
199 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
200 best available Perl editing mode in any editor.
202 For Windows editors: you can download an Emacs
208 http://www.gnu.org/software/emacs/windows/ntemacs.html
212 http://members.nbci.com/uemacs/
216 http://www.xemacs.org/Download/index.html
220 or a vi clone such as
226 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
236 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
240 For vi lovers in general, Windows or elsewhere:
241 http://www.thomer.com/thomer/vi/vi.html.
243 nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
244 yet another vi clone, unfortunately not available for Windows, but in
245 UNIX platforms you might be interested in trying it out, firstly because
246 strictly speaking it is not a vi clone, it is the real vi, or the new
247 incarnation of it, and secondly because you can embed Perl inside it
248 to use Perl as the scripting language. nvi is not alone in this,
249 though: at least also vim and vile offer an embedded Perl.
251 The following are Win32 multilanguage editor/IDESs that support Perl:
257 http://www.starbase.com/
261 http://www.MultiEdit.com/
265 http://www.slickedit.com/
269 There is also a toyedit Text widget based editor written in Perl
270 that is distributed with the Tk module on CPAN. The ptkdb
271 (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
272 acts as a development environment of sorts. Perl Composer
273 (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
276 In addition to an editor/IDE you might be interested in a more
277 powerful shell environment for Win32. Your options include
283 from the Cygwin package (http://sources.redhat.com/cygwin/)
287 from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
288 the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
292 ftp://ftp.astron.com/pub/tcsh/, see also
293 http://www.primate.wisc.edu/software/csh-tcsh-book/
297 ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
301 MKS and U/WIN are commercial (U/WIN is free for educational and
302 research purposes), Cygwin is covered by the GNU Public License (but
303 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
304 contain (in addition to the shells) a comprehensive set of standard
305 UNIX toolkit utilities.
307 If you're transferring text files between Unix and Windows using FTP
308 be sure to transfer them in ASCII mode so the ends of lines are
309 appropriately converted.
311 On Mac OS the MacPerl Application comes with a simple 32k text editor
312 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
313 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
318 =item BBEdit and BBEdit Lite
320 are text editors for Mac OS that have a Perl sensitivity mode
321 (http://web.barebones.com/).
325 is an editor, written and extensible in Tcl, that nonetheless has
326 built in support for several popular markup and programming languages
327 including Perl and HTML (http://alpha.olm.net/).
331 Pepper and Pe are programming language sensitive text editors for Mac
332 OS X and BeOS respectively (http://www.hekkelman.com/).
334 =head2 Where can I get Perl macros for vi?
336 For a complete version of Tom Christiansen's vi configuration file,
337 see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
338 the standard benchmark file for vi emulators. The file runs best with nvi,
339 the current version of vi out of Berkeley, which incidentally can be built
340 with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.
342 =head2 Where can I get perl-mode for emacs?
344 Since Emacs version 19 patchlevel 22 or so, there have been both a
345 perl-mode.el and support for the Perl debugger built in. These should
346 come with the standard Emacs 19 distribution.
348 In the Perl source directory, you'll find a directory called "emacs",
349 which contains a cperl-mode that color-codes keywords, provides
350 context-sensitive help, and other nifty things.
352 Note that the perl-mode of emacs will have fits with C<"main'foo">
353 (single quote), and mess up the indentation and highlighting. You
354 are probably using C<"main::foo"> in new Perl code anyway, so this
355 shouldn't be an issue.
357 =head2 How can I use curses with Perl?
359 The Curses module from CPAN provides a dynamically loadable object
360 module interface to a curses library. A small demo can be found at the
361 directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
362 this program repeats a command and updates the screen as needed, rendering
363 B<rep ps axu> similar to B<top>.
365 =head2 How can I use X or Tk with Perl?
367 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
368 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
369 to the Athena Widget set. Both are available from CPAN. See the
370 directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
372 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
373 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
375 http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
377 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
379 =head2 How can I generate simple menus without using CGI or Tk?
381 The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
382 module, which is curses-based, can help with this.
384 =head2 What is undump?
386 See the next question on ``How can I make my Perl program run faster?''
388 =head2 How can I make my Perl program run faster?
390 The best way to do this is to come up with a better algorithm. This
391 can often make a dramatic difference. Jon Bentley's book
392 ``Programming Pearls'' (that's not a misspelling!) has some good tips
393 on optimization, too. Advice on benchmarking boils down to: benchmark
394 and profile to make sure you're optimizing the right part, look for
395 better algorithms instead of microtuning your code, and when all else
396 fails consider just buying faster hardware.
398 A different approach is to autoload seldom-used Perl code. See the
399 AutoSplit and AutoLoader modules in the standard distribution for
400 that. Or you could locate the bottleneck and think about writing just
401 that part in C, the way we used to take bottlenecks in C code and
402 write them in assembler. Similar to rewriting in C,
403 modules that have critical sections can be written in C (for instance, the
404 PDL module from CPAN).
406 In some cases, it may be worth it to use the backend compiler to
407 produce byte code (saving compilation time) or compile into C, which
408 will certainly save compilation time and sometimes a small amount (but
409 not much) execution time. See the question about compiling your Perl
410 programs for more on the compiler--the wins aren't as obvious as you'd
413 If you're currently linking your perl executable to a shared I<libc.so>,
414 you can often gain a 10-25% performance benefit by rebuilding it to
415 link with a static libc.a instead. This will make a bigger perl
416 executable, but your Perl programs (and programmers) may thank you for
417 it. See the F<INSTALL> file in the source distribution for more
420 Unsubstantiated reports allege that Perl interpreters that use sfio
421 outperform those that don't (for I/O intensive applications). To try
422 this, see the F<INSTALL> file in the source distribution, especially
423 the ``Selecting File I/O mechanisms'' section.
425 The undump program was an old attempt to speed up your Perl program
426 by storing the already-compiled form to disk. This is no longer
427 a viable option, as it only worked on a few architectures, and
428 wasn't a good solution anyway.
430 =head2 How can I make my Perl program take less memory?
432 When it comes to time-space tradeoffs, Perl nearly always prefers to
433 throw memory at a problem. Scalars in Perl use more memory than
434 strings in C, arrays take more than that, and hashes use even more. While
435 there's still a lot to be done, recent releases have been addressing
436 these issues. For example, as of 5.004, duplicate hash keys are
437 shared amongst all hashes using them, so require no reallocation.
439 In some cases, using substr() or vec() to simulate arrays can be
440 highly beneficial. For example, an array of a thousand booleans will
441 take at least 20,000 bytes of space, but it can be turned into one
442 125-byte bit vector--a considerable memory savings. The standard
443 Tie::SubstrHash module can also help for certain types of data
444 structure. If you're working with specialist data structures
445 (matrices, for instance) modules that implement these in C may use
446 less memory than equivalent Perl modules.
448 Another thing to try is learning whether your Perl was compiled with
449 the system malloc or with Perl's builtin malloc. Whichever one it
450 is, try using the other one and see whether this makes a difference.
451 Information about malloc is in the F<INSTALL> file in the source
452 distribution. You can find out whether you are using perl's malloc by
453 typing C<perl -V:usemymalloc>.
455 =head2 Is it unsafe to return a pointer to local data?
457 No, Perl's garbage collection system takes care of this.
465 push @many, makeone();
468 print $many[4][5], "\n";
472 =head2 How can I free an array or hash so my program shrinks?
474 You can't. On most operating systems, memory allocated to a program
475 can never be returned to the system. That's why long-running programs
476 sometimes re-exec themselves. Some operating systems (notably,
477 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
478 longer used, but it doesn't appear to happen with Perl (yet). The Mac
479 appears to be the only platform that will reliably (albeit, slowly)
480 return memory to the OS.
482 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
483 $scalar> will return memory to the system, while on Solaris 2.6 it
484 won't. In general, try it yourself and see.
486 However, judicious use of my() on your variables will help make sure
487 that they go out of scope so that Perl can free up that space for
488 use in other parts of your program. A global variable, of course, never
489 goes out of scope, so you can't get its space automatically reclaimed,
490 although undef()ing and/or delete()ing it will achieve the same effect.
491 In general, memory allocation and de-allocation isn't something you can
492 or should be worrying about much in Perl, but even this capability
493 (preallocation of data types) is in the works.
495 =head2 How can I make my CGI script more efficient?
497 Beyond the normal measures described to make general Perl programs
498 faster or smaller, a CGI program has additional issues. It may be run
499 several times per second. Given that each time it runs it will need
500 to be re-compiled and will often allocate a megabyte or more of system
501 memory, this can be a killer. Compiling into C B<isn't going to help
502 you> because the process start-up overhead is where the bottleneck is.
504 There are two popular ways to avoid this overhead. One solution
505 involves running the Apache HTTP server (available from
506 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
509 With mod_perl and the Apache::Registry module (distributed with
510 mod_perl), httpd will run with an embedded Perl interpreter which
511 pre-compiles your script and then executes it within the same address
512 space without forking. The Apache extension also gives Perl access to
513 the internal server API, so modules written in Perl can do just about
514 anything a module written in C can. For more on mod_perl, see
515 http://perl.apache.org/
517 With the FCGI module (from CPAN) and the mod_fastcgi
518 module (available from http://www.fastcgi.com/) each of your Perl
519 programs becomes a permanent CGI daemon process.
521 Both of these solutions can have far-reaching effects on your system
522 and on the way you write your CGI programs, so investigate them with
525 See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
527 A non-free, commercial product, ``The Velocity Engine for Perl'',
528 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
529 might also be worth looking at. It will allow you to increase the
530 performance of your Perl programs, running programs up to 25 times
531 faster than normal CGI Perl when running in persistent Perl mode or 4
532 to 5 times faster without any modification to your existing CGI
533 programs. Fully functional evaluation copies are available from the
536 =head2 How can I hide the source for my Perl program?
538 Delete it. :-) Seriously, there are a number of (mostly
539 unsatisfactory) solutions with varying levels of ``security''.
541 First of all, however, you I<can't> take away read permission, because
542 the source code has to be readable in order to be compiled and
543 interpreted. (That doesn't mean that a CGI script's source is
544 readable by people on the web, though--only by people with access to
545 the filesystem.) So you have to leave the permissions at the socially
548 Some people regard this as a security problem. If your program does
549 insecure things and relies on people not knowing how to exploit those
550 insecurities, it is not secure. It is often possible for someone to
551 determine the insecure things and exploit them without viewing the
552 source. Security through obscurity, the name for hiding your bugs
553 instead of fixing them, is little security indeed.
555 You can try using encryption via source filters (Starting from Perl
556 5.8 the Filter::Simple and Filter::Util::Call modules are included in
557 the standard distribution), but any decent programmer will be able to
558 decrypt it. You can try using the byte code compiler and interpreter
559 described below, but the curious might still be able to de-compile it.
560 You can try using the native-code compiler described below, but
561 crackers might be able to disassemble it. These pose varying degrees
562 of difficulty to people wanting to get at your code, but none can
563 definitively conceal it (true of every language, not just Perl).
565 If you're concerned about people profiting from your code, then the
566 bottom line is that nothing but a restrictive license will give you
567 legal security. License your software and pepper it with threatening
568 statements like ``This is unpublished proprietary software of XYZ Corp.
569 Your access to it does not give you permission to use it blah blah
570 blah.'' We are not lawyers, of course, so you should see a lawyer if
571 you want to be sure your license's wording will stand up in court.
573 =head2 How can I compile my Perl program into byte code or C?
575 Malcolm Beattie has written a multifunction backend compiler,
576 available from CPAN, that can do both these things. It is included
577 in the perl5.005 release, but is still considered experimental.
578 This means it's fun to play with if you're a programmer but not
579 really for people looking for turn-key solutions.
581 Merely compiling into C does not in and of itself guarantee that your
582 code will run very much faster. That's because except for lucky cases
583 where a lot of native type inferencing is possible, the normal Perl
584 run-time system is still present and so your program will take just as
585 long to run and be just as big. Most programs save little more than
586 compilation time, leaving execution no more than 10-30% faster. A few
587 rare programs actually benefit significantly (even running several times
588 faster), but this takes some tweaking of your code.
590 You'll probably be astonished to learn that the current version of the
591 compiler generates a compiled form of your script whose executable is
592 just as big as the original perl executable, and then some. That's
593 because as currently written, all programs are prepared for a full
594 eval() statement. You can tremendously reduce this cost by building a
595 shared I<libperl.so> library and linking against that. See the
596 F<INSTALL> podfile in the Perl source distribution for details. If
597 you link your main perl binary with this, it will make it minuscule.
598 For example, on one author's system, F</usr/bin/perl> is only 11k in
601 In general, the compiler will do nothing to make a Perl program smaller,
602 faster, more portable, or more secure. In fact, it can make your
603 situation worse. The executable will be bigger, your VM system may take
604 longer to load the whole thing, the binary is fragile and hard to fix,
605 and compilation never stopped software piracy in the form of crackers,
606 viruses, or bootleggers. The real advantage of the compiler is merely
607 packaging, and once you see the size of what it makes (well, unless
608 you use a shared I<libperl.so>), you'll probably want a complete
611 =head2 How can I compile Perl into Java?
613 You can also integrate Java and Perl with the
614 Perl Resource Kit from O'Reilly and Associates. See
615 http://www.oreilly.com/catalog/prkunix/ .
617 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
618 development, allows Perl code to be called from Java. See jpl/README
619 in the Perl source tree.
621 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
625 extproc perl -S -your_switches
627 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
628 `extproc' handling). For DOS one should first invent a corresponding
629 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
630 F<INSTALL> file in the source distribution for more information).
632 The Win95/NT installation, when using the ActiveState port of Perl,
633 will modify the Registry to associate the C<.pl> extension with the
634 perl interpreter. If you install another port, perhaps even building
635 your own Win95/NT Perl from the standard sources by using a Windows port
636 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
637 the Registry yourself. In addition to associating C<.pl> with the
638 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
639 run the program C<install-linux.pl> merely by typing C<install-linux>.
641 Macintosh Perl programs will have the appropriate Creator and
642 Type, so that double-clicking them will invoke the Perl application.
644 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
645 throw the perl interpreter into your cgi-bin directory, in order to
646 get your programs working for a web server. This is an EXTREMELY big
647 security risk. Take the time to figure out how to do it correctly.
649 =head2 Can I write useful Perl programs on the command line?
651 Yes. Read L<perlrun> for more information. Some examples follow.
652 (These assume standard Unix shell quoting rules.)
654 # sum first and last fields
655 perl -lane 'print $F[0] + $F[-1]' *
657 # identify text files
658 perl -le 'for(@ARGV) {print if -f && -T _}' *
660 # remove (most) comments from C program
661 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
663 # make file a month younger than today, defeating reaper daemons
664 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
666 # find first unused uid
667 perl -le '$i++ while getpwuid($i); print $i'
669 # display reasonable manpath
670 echo $PATH | perl -nl -072 -e '
671 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
673 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
675 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
677 The problem is usually that the command interpreters on those systems
678 have rather different ideas about quoting than the Unix shells under
679 which the one-liners were created. On some systems, you may have to
680 change single-quotes to double ones, which you must I<NOT> do on Unix
681 or Plan9 systems. You might also have to change a single % to a %%.
686 perl -e 'print "Hello world\n"'
689 perl -e "print \"Hello world\n\""
692 print "Hello world\n"
693 (then Run "Myscript" or Shift-Command-R)
696 perl -e "print ""Hello world\n"""
698 The problem is that none of these examples are reliable: they depend on the
699 command interpreter. Under Unix, the first two often work. Under DOS,
700 it's entirely possible that neither works. If 4DOS was the command shell,
701 you'd probably have better luck like this:
703 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
705 Under the Mac, it depends which environment you are using. The MacPerl
706 shell, or MPW, is much like Unix shells in its support for several
707 quoting variants, except that it makes free use of the Mac's non-ASCII
708 characters as control characters.
710 Using qq(), q(), and qx(), instead of "double quotes", 'single
711 quotes', and `backticks`, may make one-liners easier to write.
713 There is no general solution to all of this. It is a mess, pure and
714 simple. Sucks to be away from Unix, huh? :-)
716 [Some of this answer was contributed by Kenneth Albanowski.]
718 =head2 Where can I learn about CGI or Web programming in Perl?
720 For modules, get the CGI or LWP modules from CPAN. For textbooks,
721 see the two especially dedicated to web stuff in the question on
722 books. For problems and questions related to the web, like ``Why
723 do I get 500 Errors'' or ``Why doesn't it run from the browser right
724 when it runs fine on the command line'', see these sources:
727 http://www.w3.org/Security/Faq/
730 http://www.boutell.com/faq/
733 http://www.webthing.com/tutorials/cgifaq.html
736 http://www.w3.org/pub/WWW/Protocols/HTTP/
739 http://www.w3.org/TR/REC-html40/
740 http://www.w3.org/pub/WWW/MarkUp/
743 http://www.w3.org/CGI/
746 http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
748 =head2 Where can I learn about object-oriented Perl programming?
750 A good place to start is L<perltoot>, and you can use L<perlobj>,
751 L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out
752 until the 5.004 release; you can get a copy (in pod, html, or
753 postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
755 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
757 If you want to call C from Perl, start with L<perlxstut>,
758 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
759 call Perl from C, then read L<perlembed>, L<perlcall>, and
760 L<perlguts>. Don't forget that you can learn a lot from looking at
761 how the authors of existing extension modules wrote their code and
762 solved their problems.
764 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
765 my C program; what am I doing wrong?
767 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
768 the tests pass, read the pods again and again and again. If they
769 fail, see L<perlbug> and send a bug report with the output of
770 C<make test TEST_VERBOSE=1> along with C<perl -V>.
772 =head2 When I tried to run my script, I got this message. What does it
775 A complete list of Perl's error messages and warnings with explanatory
776 text can be found in L<perldiag>. You can also use the splain program
777 (distributed with Perl) to explain the error messages:
779 perl program 2>diag.out
780 splain [-v] [-p] diag.out
782 or change your program to explain the messages for you:
788 use diagnostics -verbose;
790 =head2 What's MakeMaker?
792 This module (part of the standard Perl distribution) is designed to
793 write a Makefile for an extension module from a Makefile.PL. For more
794 information, see L<ExtUtils::MakeMaker>.
796 =head1 AUTHOR AND COPYRIGHT
798 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
801 When included as an integrated part of the Standard Distribution
802 of Perl or of its documentation (printed or otherwise), this works is
803 covered under Perl's Artistic License. For separate distributions of
804 all or part of this FAQ outside of that, see L<perlfaq>.
806 Irrespective of its distribution, all code examples here are in the public
807 domain. You are permitted and encouraged to use this code and any
808 derivatives thereof in your own programs for fun or for profit as you
809 see fit. A simple comment in the code giving credit to the FAQ would
810 be courteous but is not required.