3 perlfaq3 - Programming Tools ($Revision: 1.33 $, $Date: 1998/12/29 20:12:12 $)
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 Regexps 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 L<perltoc> provides a crude table of contents for the perl man page set.
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 used C<-w>? It enables warnings for dubious practices.
53 Have you tried C<use strict>? It prevents you from using symbolic
54 references, makes you predeclare any subroutines that you call as bare
55 words, and (probably most importantly) forces you to predeclare your
56 variables with C<my> or C<use vars>.
58 Did you check the returns of each and every system call? The operating
59 system (and thus Perl) tells you whether they worked or not, and if not
62 open(FH, "> /etc/cantwrite")
63 or die "Couldn't write to /etc/cantwrite: $!\n";
65 Did you read L<perltrap>? It's full of gotchas for old and new Perl
66 programmers, and even has sections for those of you who are upgrading
67 from languages like I<awk> and I<C>.
69 Have you tried the Perl debugger, described in L<perldebug>? You can
70 step through your program and see what it's doing and thus work out
71 why what it's doing isn't what it should be doing.
73 =head2 How do I profile my Perl programs?
75 You should get the Devel::DProf module from CPAN, and also use
76 Benchmark.pm from the standard distribution. Benchmark lets you time
77 specific portions of your code, while Devel::DProf gives detailed
78 breakdowns of where your code spends its time.
80 Here's a sample use of Benchmark:
84 @junk = `cat /etc/motd`;
88 'map' => sub { my @a = @junk;
92 'for' => sub { my @a = @junk;
98 This is what it prints (on one machine--your results will be dependent
99 on your hardware, operating system, and the load on your machine):
101 Benchmark: timing 10000 iterations of for, map...
102 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
103 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
105 Be aware that a good benchmark is very hard to write. It only tests the
106 data you give it, and really proves little about differing complexities
107 of contrasting algorithms.
109 =head2 How do I cross-reference my Perl programs?
111 The B::Xref module, shipped with the new, alpha-release Perl compiler
112 (not the general distribution prior to the 5.005 release), can be used
113 to generate cross-reference reports for Perl programs.
115 perl -MO=Xref[,OPTIONS] scriptname.plx
117 =head2 Is there a pretty-printer (formatter) for Perl?
119 There is no program that will reformat Perl as much as indent(1) does
120 for C. The complex feedback between the scanner and the parser (this
121 feedback is what confuses the vgrind and emacs programs) makes it
122 challenging at best to write a stand-alone Perl parser.
124 Of course, if you simply follow the guidelines in L<perlstyle>, you
125 shouldn't need to reformat. The habit of formatting your code as you
126 write it will help prevent bugs. Your editor can and should help you
127 with this. The perl-mode for emacs can provide a remarkable amount of
128 help with most (but not all) code, and even less programmable editors
129 can provide significant assistance. Tom swears by the following
130 settings in vi and its clones:
135 Now put that in your F<.exrc> file (replacing the caret characters
136 with control characters) and away you go. In insert mode, ^T is
137 for indenting, ^D is for undenting, and ^O is for blockdenting --
138 as it were. If you haven't used the last one, you're missing
139 a lot. A more complete example, with comments, can be found at
140 http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz
142 If you are used to using the I<vgrind> program for printing out nice code
143 to a laser printer, you can take a stab at this using
144 http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
145 results are not particularly satisfying for sophisticated code.
147 The a2ps at http://www.infres.enst.fr/~demaille/a2ps/ does lots of things
148 related to generating nicely printed output of documents.
150 =head2 Is there a etags/ctags for perl?
152 With respect to the source code for the Perl interpreter, yes.
153 There has been support for etags in the source for a long time.
154 Ctags was introduced in v5.005_54 (and probably 5.005_03).
155 After building perl, type 'make etags' or 'make ctags' and both
156 sets of tag files will be built.
158 Now, if you're looking to build a tag file for perl code, then there's
160 http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
161 the trick. And if not, it's easy to hack into what you want.
163 =head2 Is there an IDE or Windows Perl Editor?
165 If you're on Unix, you already have an IDE -- Unix itself.
166 You just have to learn the toolbox. If you're not, then you
167 probably don't have a toolbox, so may need something else.
169 PerlBuilder (XXX URL to follow) is an integrated development
170 environment for Windows that supports Perl development. Perl programs
171 are just plain text, though, so you could download emacs for Windows
172 (XXX) or vim for win32 (http://www.cs.vu.nl/~tmgil/vi.html). If
173 you're transferring Windows files to Unix, be sure to transfer in
174 ASCII mode so the ends of lines are appropriately converted.
176 =head2 Where can I get Perl macros for vi?
178 For a complete version of Tom Christiansen's vi configuration file,
179 see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz,
180 the standard benchmark file for vi emulators. This runs best with nvi,
181 the current version of vi out of Berkeley, which incidentally can be built
182 with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc.
184 =head2 Where can I get perl-mode for emacs?
186 Since Emacs version 19 patchlevel 22 or so, there have been both a
187 perl-mode.el and support for the perl debugger built in. These should
188 come with the standard Emacs 19 distribution.
190 In the perl source directory, you'll find a directory called "emacs",
191 which contains a cperl-mode that color-codes keywords, provides
192 context-sensitive help, and other nifty things.
194 Note that the perl-mode of emacs will have fits with C<"main'foo">
195 (single quote), and mess up the indentation and hilighting. You
196 are probably using C<"main::foo"> in new Perl code anyway, so this
197 shouldn't be an issue.
199 =head2 How can I use curses with Perl?
201 The Curses module from CPAN provides a dynamically loadable object
202 module interface to a curses library. A small demo can be found at the
203 directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
204 this program repeats a command and updates the screen as needed, rendering
205 B<rep ps axu> similar to B<top>.
207 =head2 How can I use X or Tk with Perl?
209 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
210 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
211 to the Athena Widget set. Both are available from CPAN. See the
212 directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
214 Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at
215 http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the Perl/Tk Reference
217 http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
219 http://www-users.cs.umn.edu/~amundson/perl/perltk/toc.html .
221 =head2 How can I generate simple menus without using CGI or Tk?
223 The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
224 module, which is curses-based, can help with this.
226 =head2 What is undump?
228 See the next questions.
230 =head2 How can I make my Perl program run faster?
232 The best way to do this is to come up with a better algorithm. This
233 can often make a dramatic difference. Chapter 8 in the Camel has some
234 efficiency tips in it you might want to look at. Jon Bentley's book
235 ``Programming Pearls'' (that's not a misspelling!) has some good tips
236 on optimization, too. Advice on benchmarking boils down to: benchmark
237 and profile to make sure you're optimizing the right part, look for
238 better algorithms instead of microtuning your code, and when all else
239 fails consider just buying faster hardware.
241 A different approach is to autoload seldom-used Perl code. See the
242 AutoSplit and AutoLoader modules in the standard distribution for
243 that. Or you could locate the bottleneck and think about writing just
244 that part in C, the way we used to take bottlenecks in C code and
245 write them in assembler. Similar to rewriting in C is the use of
246 modules that have critical sections written in C (for instance, the
247 PDL module from CPAN).
249 In some cases, it may be worth it to use the backend compiler to
250 produce byte code (saving compilation time) or compile into C, which
251 will certainly save compilation time and sometimes a small amount (but
252 not much) execution time. See the question about compiling your Perl
253 programs for more on the compiler--the wins aren't as obvious as you'd
256 If you're currently linking your perl executable to a shared I<libc.so>,
257 you can often gain a 10-25% performance benefit by rebuilding it to
258 link with a static libc.a instead. This will make a bigger perl
259 executable, but your Perl programs (and programmers) may thank you for
260 it. See the F<INSTALL> file in the source distribution for more
263 Unsubstantiated reports allege that Perl interpreters that use sfio
264 outperform those that don't (for IO intensive applications). To try
265 this, see the F<INSTALL> file in the source distribution, especially
266 the ``Selecting File IO mechanisms'' section.
268 The undump program was an old attempt to speed up your Perl program
269 by storing the already-compiled form to disk. This is no longer
270 a viable option, as it only worked on a few architectures, and
271 wasn't a good solution anyway.
273 =head2 How can I make my Perl program take less memory?
275 When it comes to time-space tradeoffs, Perl nearly always prefers to
276 throw memory at a problem. Scalars in Perl use more memory than
277 strings in C, arrays take more than that, and hashes use even more. While
278 there's still a lot to be done, recent releases have been addressing
279 these issues. For example, as of 5.004, duplicate hash keys are
280 shared amongst all hashes using them, so require no reallocation.
282 In some cases, using substr() or vec() to simulate arrays can be
283 highly beneficial. For example, an array of a thousand booleans will
284 take at least 20,000 bytes of space, but it can be turned into one
285 125-byte bit vector for a considerable memory savings. The standard
286 Tie::SubstrHash module can also help for certain types of data
287 structure. If you're working with specialist data structures
288 (matrices, for instance) modules that implement these in C may use
289 less memory than equivalent Perl modules.
291 Another thing to try is learning whether your Perl was compiled with
292 the system malloc or with Perl's builtin malloc. Whichever one it
293 is, try using the other one and see whether this makes a difference.
294 Information about malloc is in the F<INSTALL> file in the source
295 distribution. You can find out whether you are using perl's malloc by
296 typing C<perl -V:usemymalloc>.
298 =head2 Is it unsafe to return a pointer to local data?
300 No, Perl's garbage collection system takes care of this.
308 push @many, makeone();
311 print $many[4][5], "\n";
315 =head2 How can I free an array or hash so my program shrinks?
317 You can't. On most operating systems, memory allocated to a program
318 can never be returned to the system. That's why long-running programs
319 sometimes re-exec themselves. Some operating systems (notably,
320 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
321 longer used, but it doesn't appear to happen with Perl (yet). The Mac
322 appears to be the only platform that will reliably (albeit, slowly)
323 return memory to the OS.
325 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
326 $scalar> will return memory to the system, while on Solaris 2.6 it
327 won't. In general, try it yourself and see.
329 However, judicious use of my() on your variables will help make sure
330 that they go out of scope so that Perl can free up their storage for
331 use in other parts of your program. A global variable, of course, never
332 goes out of scope, so you can't get its space automatically reclaimed,
333 although undef()ing and/or delete()ing it will achieve the same effect.
334 In general, memory allocation and de-allocation isn't something you can
335 or should be worrying about much in Perl, but even this capability
336 (preallocation of data types) is in the works.
338 =head2 How can I make my CGI script more efficient?
340 Beyond the normal measures described to make general Perl programs
341 faster or smaller, a CGI program has additional issues. It may be run
342 several times per second. Given that each time it runs it will need
343 to be re-compiled and will often allocate a megabyte or more of system
344 memory, this can be a killer. Compiling into C B<isn't going to help
345 you> because the process start-up overhead is where the bottleneck is.
347 There are two popular ways to avoid this overhead. One solution
348 involves running the Apache HTTP server (available from
349 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
352 With mod_perl and the Apache::Registry module (distributed with
353 mod_perl), httpd will run with an embedded Perl interpreter which
354 pre-compiles your script and then executes it within the same address
355 space without forking. The Apache extension also gives Perl access to
356 the internal server API, so modules written in Perl can do just about
357 anything a module written in C can. For more on mod_perl, see
358 http://perl.apache.org/
360 With the FCGI module (from CPAN) and the mod_fastcgi
361 module (available from http://www.fastcgi.com/) each of your perl
362 scripts becomes a permanent CGI daemon process.
364 Both of these solutions can have far-reaching effects on your system
365 and on the way you write your CGI scripts, so investigate them with
368 See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
370 A non-free, commercial product, ``The Velocity Engine for Perl'',
371 (http://www.binevolve.com/ or
372 also be worth looking at. It will allow you to increase the performance
373 of your perl scripts, upto 25 times faster than normal CGI perl by
374 running in persistent perl mode, or 4 to 5 times faster without any
375 modification to your existing CGI scripts. Fully functional evaluation
376 copies are available from the web site.
378 =head2 How can I hide the source for my Perl program?
380 Delete it. :-) Seriously, there are a number of (mostly
381 unsatisfactory) solutions with varying levels of ``security''.
383 First of all, however, you I<can't> take away read permission, because
384 the source code has to be readable in order to be compiled and
385 interpreted. (That doesn't mean that a CGI script's source is
386 readable by people on the web, though, only by people with access to
387 the filesystem) So you have to leave the permissions at the socially
390 Some people regard this as a security problem. If your program does
391 insecure things, and relies on people not knowing how to exploit those
392 insecurities, it is not secure. It is often possible for someone to
393 determine the insecure things and exploit them without viewing the
394 source. Security through obscurity, the name for hiding your bugs
395 instead of fixing them, is little security indeed.
397 You can try using encryption via source filters (Filter::* from CPAN),
398 but any decent programmer will be able to decrypt it. You can try using
399 the byte code compiler and interpreter described below, but the curious
400 might still be able to de-compile it. You can try using the native-code
401 compiler described below, but crackers might be able to disassemble it.
402 These pose varying degrees of difficulty to people wanting to get at
403 your code, but none can definitively conceal it (this is true of every
404 language, not just Perl).
406 If you're concerned about people profiting from your code, then the
407 bottom line is that nothing but a restrictive licence will give you
408 legal security. License your software and pepper it with threatening
409 statements like ``This is unpublished proprietary software of XYZ Corp.
410 Your access to it does not give you permission to use it blah blah
411 blah.'' We are not lawyers, of course, so you should see a lawyer if
412 you want to be sure your licence's wording will stand up in court.
414 =head2 How can I compile my Perl program into byte code or C?
416 Malcolm Beattie has written a multifunction backend compiler,
417 available from CPAN, that can do both these things. It is included
418 in the perl5.005 release, but is still considered experimental.
419 This means it's fun to play with if you're a programmer but not
420 really for people looking for turn-key solutions.
422 Merely compiling into C does not in and of itself guarantee that your
423 code will run very much faster. That's because except for lucky cases
424 where a lot of native type inferencing is possible, the normal Perl
425 run time system is still present and so your program will take just as
426 long to run and be just as big. Most programs save little more than
427 compilation time, leaving execution no more than 10-30% faster. A few
428 rare programs actually benefit significantly (like several times
429 faster), but this takes some tweaking of your code.
431 You'll probably be astonished to learn that the current version of the
432 compiler generates a compiled form of your script whose executable is
433 just as big as the original perl executable, and then some. That's
434 because as currently written, all programs are prepared for a full
435 eval() statement. You can tremendously reduce this cost by building a
436 shared I<libperl.so> library and linking against that. See the
437 F<INSTALL> podfile in the perl source distribution for details. If
438 you link your main perl binary with this, it will make it miniscule.
439 For example, on one author's system, F</usr/bin/perl> is only 11k in
442 In general, the compiler will do nothing to make a Perl program smaller,
443 faster, more portable, or more secure. In fact, it will usually hurt
444 all of those. The executable will be bigger, your VM system may take
445 longer to load the whole thing, the binary is fragile and hard to fix,
446 and compilation never stopped software piracy in the form of crackers,
447 viruses, or bootleggers. The real advantage of the compiler is merely
448 packaging, and once you see the size of what it makes (well, unless
449 you use a shared I<libperl.so>), you'll probably want a complete
452 =head2 How can I compile Perl into Java?
454 You can't. Not yet, anyway. You can integrate Java and Perl with the
455 Perl Resource Kit from O'Reilly and Associates. See
456 http://www.oreilly.com/catalog/prkunix/ for more information.
457 The Java interface will be supported in the core 5.006 release
460 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
464 extproc perl -S -your_switches
466 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
467 `extproc' handling). For DOS one should first invent a corresponding
468 batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the
469 F<INSTALL> file in the source distribution for more information).
471 The Win95/NT installation, when using the ActiveState port of Perl,
472 will modify the Registry to associate the C<.pl> extension with the
473 perl interpreter. If you install another port (Gurusamy Sarathy's is
474 the recommended Win95/NT port), or (eventually) build your own
475 Win95/NT Perl using a Windows port of gcc (e.g., with cygwin32 or
476 mingw32), then you'll have to modify the Registry yourself. In
477 addition to associating C<.pl> with the interpreter, NT people can
478 use: C<SET PATHEXT=%PATHEXT%;.PL> to let them run the program
479 C<install-linux.pl> merely by typing C<install-linux>.
481 Macintosh perl scripts will have the appropriate Creator and
482 Type, so that double-clicking them will invoke the perl application.
484 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
485 throw the perl interpreter into your cgi-bin directory, in order to
486 get your scripts working for a web server. This is an EXTREMELY big
487 security risk. Take the time to figure out how to do it correctly.
489 =head2 Can I write useful perl programs on the command line?
491 Yes. Read L<perlrun> for more information. Some examples follow.
492 (These assume standard Unix shell quoting rules.)
494 # sum first and last fields
495 perl -lane 'print $F[0] + $F[-1]' *
497 # identify text files
498 perl -le 'for(@ARGV) {print if -f && -T _}' *
500 # remove (most) comments from C program
501 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
503 # make file a month younger than today, defeating reaper daemons
504 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
506 # find first unused uid
507 perl -le '$i++ while getpwuid($i); print $i'
509 # display reasonable manpath
510 echo $PATH | perl -nl -072 -e '
511 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
513 Ok, the last one was actually an obfuscated perl entry. :-)
515 =head2 Why don't perl one-liners work on my DOS/Mac/VMS system?
517 The problem is usually that the command interpreters on those systems
518 have rather different ideas about quoting than the Unix shells under
519 which the one-liners were created. On some systems, you may have to
520 change single-quotes to double ones, which you must I<NOT> do on Unix
521 or Plan9 systems. You might also have to change a single % to a %%.
526 perl -e 'print "Hello world\n"'
529 perl -e "print \"Hello world\n\""
532 print "Hello world\n"
533 (then Run "Myscript" or Shift-Command-R)
536 perl -e "print ""Hello world\n"""
538 The problem is that none of this is reliable: it depends on the
539 command interpreter. Under Unix, the first two often work. Under DOS,
540 it's entirely possible neither works. If 4DOS was the command shell,
541 you'd probably have better luck like this:
543 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
545 Under the Mac, it depends which environment you are using. The MacPerl
546 shell, or MPW, is much like Unix shells in its support for several
547 quoting variants, except that it makes free use of the Mac's non-ASCII
548 characters as control characters.
550 Using qq(), q(), and qx(), instead of "double quotes", 'single
551 quotes', and `backticks`, may make one-liners easier to write.
553 There is no general solution to all of this. It is a mess, pure and
554 simple. Sucks to be away from Unix, huh? :-)
556 [Some of this answer was contributed by Kenneth Albanowski.]
558 =head2 Where can I learn about CGI or Web programming in Perl?
560 For modules, get the CGI or LWP modules from CPAN. For textbooks,
561 see the two especially dedicated to web stuff in the question on
562 books. For problems and questions related to the web, like ``Why
563 do I get 500 Errors'' or ``Why doesn't it run from the browser right
564 when it runs fine on the command line'', see these sources:
567 http://www.w3.org/Security/Faq/
570 http://www.boutell.com/faq/
573 http://www.webthing.com/tutorials/cgifaq.html
576 http://www.w3.org/pub/WWW/Protocols/HTTP/
579 http://www.w3.org/TR/REC-html40/
580 http://www.w3.org/pub/WWW/MarkUp/
583 http://www.w3.org/CGI/
586 http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
588 Also take a look at L<perlfaq9>
590 =head2 Where can I learn about object-oriented Perl programming?
592 L<perltoot> is a good place to start, and you can use L<perlobj> and
593 L<perlbot> for reference. Perltoot didn't come out until the 5.004
594 release, but you can get a copy (in pod, html, or postscript) from
595 http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
597 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
599 If you want to call C from Perl, start with L<perlxstut>,
600 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
601 call Perl from C, then read L<perlembed>, L<perlcall>, and
602 L<perlguts>. Don't forget that you can learn a lot from looking at
603 how the authors of existing extension modules wrote their code and
604 solved their problems.
606 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
607 my C program, what am I doing wrong?
609 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
610 the tests pass, read the pods again and again and again. If they
611 fail, see L<perlbug> and send a bugreport with the output of
612 C<make test TEST_VERBOSE=1> along with C<perl -V>.
614 =head2 When I tried to run my script, I got this message. What does it
617 L<perldiag> has a complete list of perl's error messages and warnings,
618 with explanatory text. You can also use the splain program (distributed
619 with perl) to explain the error messages:
621 perl program 2>diag.out
622 splain [-v] [-p] diag.out
624 or change your program to explain the messages for you:
630 use diagnostics -verbose;
632 =head2 What's MakeMaker?
634 This module (part of the standard perl distribution) is designed to
635 write a Makefile for an extension module from a Makefile.PL. For more
636 information, see L<ExtUtils::MakeMaker>.
638 =head1 AUTHOR AND COPYRIGHT
640 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
643 When included as an integrated part of the Standard Distribution
644 of Perl or of its documentation (printed or otherwise), this work is
645 covered under Perl's Artistic Licence. For separate distributions of
646 all or part of this FAQ outside of that, see L<perlfaq>.
648 Irrespective of its distribution, all code examples here are public
649 domain. You are permitted and encouraged to use this code and any
650 derivatives thereof in your own programs for fun or for profit as you
651 see fit. A simple comment in the code giving credit to the FAQ would
652 be courteous but is not required.