PERLFAQ3(1)      Perl Programmers Reference Guide     PERLFAQ3(1)

NNAAMMEE
       perlfaq3 - Programming Tools ($Revision: 1.33 $, $Date:
       1998/12/29 20:12:12 $)

DDEESSCCRRIIPPTTIIOONN
       This section of the FAQ answers questions related to
       programmer tools and programming support.

       HHooww ddoo II ddoo ((aannyytthhiinngg))??

       Have you looked at CPAN (see the perlfaq2 manpage)?  The
       chances are that someone has already written a module that
       can solve your problem.  Have you read the appropriate man
       pages?  Here's a brief index:

               Basics          perldata, perlvar, perlsyn, perlop, perlsub
               Execution       perlrun, perldebug
               Functions       perlfunc
               Objects         perlref, perlmod, perlobj, perltie
               Data Structures perlref, perllol, perldsc
               Modules         perlmod, perlmodlib, perlsub
               Regexps         perlre, perlfunc, perlop, perllocale
               Moving to perl5 perltrap, perl
               Linking w/C     perlxstut, perlxs, perlcall, perlguts, perlembed
               Various         http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html
                               (not a man-page but still useful)

       the perltoc manpage provides a crude table of contents for
       the perl man page set.

       HHooww ccaann II uussee PPeerrll iinntteerraaccttiivveellyy??

       The typical approach uses the Perl debugger, described in
       the perldebug(1) man page, on an ``empty'' program, like
       this:

           perl -de 42

       Now just type in any legal Perl code, and it will be
       immediately evaluated.  You can also examine the symbol
       table, get stack backtraces, check variable values, set
       breakpoints, and other operations typically found in
       symbolic debuggers.

       IIss tthheerree aa PPeerrll sshheellll??

       In general, no.  The Shell.pm module (distributed with
       perl) makes perl try commands which aren't part of the
       Perl language as shell commands.  perlsh from the source
       distribution is simplistic and uninteresting, but may
       still be what you want.

       HHooww ddoo II ddeebbuugg mmyy PPeerrll pprrooggrraammss??

       Have you used -w?  It enables warnings for dubious
       practices.

       Have you tried use strict?  It prevents you from using
       symbolic references, makes you predeclare any subroutines
       that you call as bare words, and (probably most
       importantly) forces you to predeclare your variables with
       my or use vars.

       Did you check the returns of each and every system call?
       The operating system (and thus Perl) tells you whether
       they worked or not, and if not why.

         open(FH, "> /etc/cantwrite")
           or die "Couldn't write to /etc/cantwrite: $!\n";

       Did you read the perltrap manpage?  It's full of gotchas
       for old and new Perl programmers, and even has sections
       for those of you who are upgrading from languages like awk
       and C.

       Have you tried the Perl debugger, described in the
       perldebug manpage?  You can step through your program and
       see what it's doing and thus work out why what it's doing
       isn't what it should be doing.

       HHooww ddoo II pprrooffiillee mmyy PPeerrll pprrooggrraammss??

       You should get the Devel::DProf module from CPAN, and also
       use Benchmark.pm from the standard distribution.
       Benchmark lets you time specific portions of your code,
       while Devel::DProf gives detailed breakdowns of where your
       code spends its time.

       Here's a sample use of Benchmark:

         use Benchmark;

         @junk = `cat /etc/motd`;
         $count = 10_000;

         timethese($count, {
                   'map' => sub { my @a = @junk;
                                  map { s/a/b/ } @a;
                                  return @a
                                },
                   'for' => sub { my @a = @junk;
                                  local $_;
                                  for (@a) { s/a/b/ };
                                  return @a },
                  });

       This is what it prints (on one machine--your results will
       be dependent on your hardware, operating system, and the
       load on your machine):

         Benchmark: timing 10000 iterations of for, map...
                for:  4 secs ( 3.97 usr  0.01 sys =  3.98 cpu)
                map:  6 secs ( 4.97 usr  0.00 sys =  4.97 cpu)

       Be aware that a good benchmark is very hard to write.  It
       only tests the data you give it, and really proves little
       about differing complexities of contrasting algorithms.

       HHooww ddoo II ccrroossss--rreeffeerreennccee mmyy PPeerrll pprrooggrraammss??

       The B::Xref module, shipped with the new, alpha-release
       Perl compiler (not the general distribution prior to the
       5.005 release), can be used to generate cross-reference
       reports for Perl programs.

           perl -MO=Xref[,OPTIONS] scriptname.plx

       IIss tthheerree aa pprreettttyy--pprriinntteerr ((ffoorrmmaatttteerr)) ffoorr PPeerrll??

       There is no program that will reformat Perl as much as
       indent(1) does for C.  The complex feedback between the
       scanner and the parser (this feedback is what confuses the
       vgrind and emacs programs) makes it challenging at best to
       write a stand-alone Perl parser.

       Of course, if you simply follow the guidelines in the
       perlstyle manpage, you shouldn't need to reformat.  The
       habit of formatting your code as you write it will help
       prevent bugs.  Your editor can and should help you with
       this.  The perl-mode for emacs can provide a remarkable
       amount of help with most (but not all) code, and even less
       programmable editors can provide significant assistance.
       Tom swears by the following settings in vi and its clones:

           set ai sw=4
           map ^O {^M}^[O^T

       Now put that in your .exrc file (replacing the caret
       characters with control characters) and away you go.  In
       insert mode, ^T is for indenting, ^D is for undenting, and
       ^O is for blockdenting -- as it were.  If you haven't used
       the last one, you're missing a lot.  A more complete
       example, with comments, can be found at
       http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz

       If you are used to using the vgrind program for printing
       out nice code to a laser printer, you can take a stab at
       this using
       http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry,
       but the results are not particularly satisfying for
       sophisticated code.

       The a2ps at http://www.infres.enst.fr/~demaille/a2ps/ does
       lots of things related to generating nicely printed output
       of documents.

       IIss tthheerree aa eettaaggss//ccttaaggss ffoorr ppeerrll??

       With respect to the source code for the Perl interpreter,
       yes.  There has been support for etags in the source for a
       long time.  Ctags was introduced in v5.005_54 (and
       probably 5.005_03).  After building perl, type 'make
       etags' or 'make ctags' and both sets of tag files will be
       built.

       Now, if you're looking to build a tag file for perl code,
       then there's a simple one at
       http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz
       which may do the trick.  And if not, it's easy to hack
       into what you want.

       IIss tthheerree aann IIDDEE oorr WWiinnddoowwss PPeerrll EEddiittoorr??

       If you're on Unix, you already have an IDE -- Unix itself.
       You just have to learn the toolbox.  If you're not, then
       you probably don't have a toolbox, so may need something
       else.

       PerlBuilder (XXX URL to follow) is an integrated
       development environment for Windows that supports Perl
       development.  Perl programs are just plain text, though,
       so you could download emacs for Windows (XXX) or vim for
       win32 (http://www.cs.vu.nl/~tmgil/vi.html).  If you're
       transferring Windows files to Unix, be sure to transfer in
       ASCII mode so the ends of lines are appropriately
       converted.

       WWhheerree ccaann II ggeett PPeerrll mmaaccrrooss ffoorr vvii??

       For a complete version of Tom Christiansen's vi
       configuration file, see
       http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz,
       the standard benchmark file for vi emulators.  This runs
       best with nvi, the current version of vi out of Berkeley,
       which incidentally can be built with an embedded Perl
       interpreter -- see http://www.perl.com/CPAN/src/misc.

       WWhheerree ccaann II ggeett ppeerrll--mmooddee ffoorr eemmaaccss??

       Since Emacs version 19 patchlevel 22 or so, there have
       been both a perl-mode.el and support for the perl debugger
       built in.  These should come with the standard Emacs 19
       distribution.

       In the perl source directory, you'll find a directory
       called "emacs", which contains a cperl-mode that color-
       codes keywords, provides context-sensitive help, and other
       nifty things.

       Note that the perl-mode of emacs will have fits with
       "main'foo" (single quote), and mess up the indentation and
       hilighting.  You are probably using "main::foo" in new
       Perl code anyway, so this shouldn't be an issue.

       HHooww ccaann II uussee ccuurrsseess wwiitthh PPeerrll??

       The Curses module from CPAN provides a dynamically
       loadable object module interface to a curses library.  A
       small demo can be found at the directory
       http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
       this program repeats a command and updates the screen as
       needed, rendering rreepp ppss aaxxuu similar to ttoopp.

       HHooww ccaann II uussee XX oorr TTkk wwiitthh PPeerrll??

       Tk is a completely Perl-based, object-oriented interface
       to the Tk toolkit that doesn't force you to use Tcl just
       to get at Tk.  Sx is an interface to the Athena Widget
       set.  Both are available from CPAN.  See the directory
       http://www.perl.com/CPAN/modules/by-
       category/08_User_Interfaces/

       Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at
       http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the
       Perl/Tk Reference Guide available at
       http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ ,
       and the online manpages at http://www-
       users.cs.umn.edu/~amundson/perl/perltk/toc.html .

       HHooww ccaann II ggeenneerraattee ssiimmppllee mmeennuuss wwiitthhoouutt uussiinngg CCGGII oorr TTkk??

       The
       http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
       module, which is curses-based, can help with this.

       WWhhaatt iiss uunndduummpp??

       See the next questions.

       HHooww ccaann II mmaakkee mmyy PPeerrll pprrooggrraamm rruunn ffaasstteerr??

       The best way to do this is to come up with a better
       algorithm.  This can often make a dramatic difference.
       Chapter 8 in the Camel has some efficiency tips in it you
       might want to look at.  Jon Bentley's book ``Programming
       Pearls'' (that's not a misspelling!)  has some good tips
       on optimization, too.  Advice on benchmarking boils down
       to: benchmark and profile to make sure you're optimizing
       the right part, look for better algorithms instead of
       microtuning your code, and when all else fails consider
       just buying faster hardware.

       A different approach is to autoload seldom-used Perl code.
       See the AutoSplit and AutoLoader modules in the standard
       distribution for that.  Or you could locate the bottleneck
       and think about writing just that part in C, the way we
       used to take bottlenecks in C code and write them in
       assembler.  Similar to rewriting in C is the use of
       modules that have critical sections written in C (for
       instance, the PDL module from CPAN).

       In some cases, it may be worth it to use the backend
       compiler to produce byte code (saving compilation time) or
       compile into C, which will certainly save compilation time
       and sometimes a small amount (but not much) execution
       time.  See the question about compiling your Perl programs
       for more on the compiler--the wins aren't as obvious as
       you'd hope.

       If you're currently linking your perl executable to a
       shared libc.so, you can often gain a 10-25% performance
       benefit by rebuilding it to link with a static libc.a
       instead.  This will make a bigger perl executable, but
       your Perl programs (and programmers) may thank you for it.
       See the INSTALL file in the source distribution for more
       information.

       Unsubstantiated reports allege that Perl interpreters that
       use sfio outperform those that don't (for IO intensive
       applications).  To try this, see the INSTALL file in the
       source distribution, especially the ``Selecting File IO
       mechanisms'' section.

       The undump program was an old attempt to speed up your
       Perl program by storing the already-compiled form to disk.
       This is no longer a viable option, as it only worked on a
       few architectures, and wasn't a good solution anyway.

       HHooww ccaann II mmaakkee mmyy PPeerrll pprrooggrraamm ttaakkee lleessss mmeemmoorryy??

       When it comes to time-space tradeoffs, Perl nearly always
       prefers to throw memory at a problem.  Scalars in Perl use
       more memory than strings in C, arrays take more than that,
       and hashes use even more.  While there's still a lot to be
       done, recent releases have been addressing these issues.
       For example, as of 5.004, duplicate hash keys are shared
       amongst all hashes using them, so require no reallocation.

       In some cases, using substr() or vec() to simulate arrays
       can be highly beneficial.  For example, an array of a
       thousand booleans will take at least 20,000 bytes of
       space, but it can be turned into one 125-byte bit vector
       for a considerable memory savings.  The standard
       Tie::SubstrHash module can also help for certain types of
       data structure.  If you're working with specialist data
       structures (matrices, for instance) modules that implement
       these in C may use less memory than equivalent Perl
       modules.

       Another thing to try is learning whether your Perl was
       compiled with the system malloc or with Perl's builtin
       malloc.  Whichever one it is, try using the other one and
       see whether this makes a difference.  Information about
       malloc is in the INSTALL file in the source distribution.
       You can find out whether you are using perl's malloc by
       typing perl -V:usemymalloc.

       IIss iitt uunnssaaffee ttoo rreettuurrnn aa ppooiinntteerr ttoo llooccaall ddaattaa??

       No, Perl's garbage collection system takes care of this.

           sub makeone {
               my @a = ( 1 .. 10 );
               return \@a;
           }

           for $i ( 1 .. 10 ) {
               push @many, makeone();
           }

           print $many[4][5], "\n";

           print "@many\n";

       HHooww ccaann II ffrreeee aann aarrrraayy oorr hhaasshh ssoo mmyy pprrooggrraamm sshhrriinnkkss??

       You can't.  On most operating systems, memory allocated to
       a program can never be returned to the system.  That's why
       long-running programs sometimes re-exec themselves.  Some
       operating systems (notably, FreeBSD and Linux) allegedly
       reclaim large chunks of memory that is no longer used, but
       it doesn't appear to happen with Perl (yet).  The Mac
       appears to be the only platform that will reliably
       (albeit, slowly) return memory to the OS.

       We've had reports that on Linux (Redhat 5.1) on Intel,
       undef $scalar will return memory to the system, while on
       Solaris 2.6 it won't.  In general, try it yourself and
       see.

       However, judicious use of my() on your variables will help
       make sure that they go out of scope so that Perl can free
       up their storage for use in other parts of your program.
       A global variable, of course, never goes out of scope, so
       you can't get its space automatically reclaimed, although
       undef()ing and/or delete()ing it will achieve the same
       effect.  In general, memory allocation and de-allocation
       isn't something you can or should be worrying about much
       in Perl, but even this capability (preallocation of data
       types) is in the works.

       HHooww ccaann II mmaakkee mmyy CCGGII ssccrriipptt mmoorree eeffffiicciieenntt??

       Beyond the normal measures described to make general Perl
       programs faster or smaller, a CGI program has additional
       issues.  It may be run several times per second.  Given
       that each time it runs it will need to be re-compiled and
       will often allocate a megabyte or more of system memory,
       this can be a killer.  Compiling into C iissnn''tt ggooiinngg ttoo
       hheellpp yyoouu because the process start-up overhead is where
       the bottleneck is.

       There are two popular ways to avoid this overhead.  One
       solution involves running the Apache HTTP server
       (available from http://www.apache.org/) with either of the
       mod_perl or mod_fastcgi plugin modules.

       With mod_perl and the Apache::Registry module (distributed
       with mod_perl), httpd will run with an embedded Perl
       interpreter which pre-compiles your script and then
       executes it within the same address space without forking.
       The Apache extension also gives Perl access to the
       internal server API, so modules written in Perl can do
       just about anything a module written in C can.  For more
       on mod_perl, see http://perl.apache.org/

       With the FCGI module (from CPAN) and the mod_fastcgi
       module (available from http://www.fastcgi.com/) each of
       your perl scripts becomes a permanent CGI daemon process.

       Both of these solutions can have far-reaching effects on
       your system and on the way you write your CGI scripts, so
       investigate them with care.

       See http://www.perl.com/CPAN/modules/by-
       category/15_World_Wide_Web_HTML_HTTP_CGI/ .

       A non-free, commercial product, ``The Velocity Engine for
       Perl'', (http://www.binevolve.com/ or also be worth
       looking at.  It will allow you to increase the performance
       of your perl scripts, upto 25 times faster than normal CGI
       perl by running in persistent perl mode, or 4 to 5 times
       faster without any modification to your existing CGI
       scripts. Fully functional evaluation copies are available
       from the web site.

       HHooww ccaann II hhiiddee tthhee ssoouurrccee ffoorr mmyy PPeerrll pprrooggrraamm??

       Delete it. :-) Seriously, there are a number of (mostly
       unsatisfactory) solutions with varying levels of
       ``security''.

       First of all, however, you can't take away read
       permission, because the source code has to be readable in
       order to be compiled and interpreted.  (That doesn't mean
       that a CGI script's source is readable by people on the
       web, though, only by people with access to the filesystem)
       So you have to leave the permissions at the socially
       friendly 0755 level.

       Some people regard this as a security problem.  If your
       program does insecure things, and relies on people not
       knowing how to exploit those insecurities, it is not
       secure.  It is often possible for someone to determine the
       insecure things and exploit them without viewing the
       source.  Security through obscurity, the name for hiding
       your bugs instead of fixing them, is little security
       indeed.

       You can try using encryption via source filters (Filter::*
       from CPAN), but any decent programmer will be able to
       decrypt it.  You can try using the byte code compiler and
       interpreter described below, but the curious might still
       be able to de-compile it.  You can try using the native-
       code compiler described below, but crackers might be able
       to disassemble it.  These pose varying degrees of
       difficulty to people wanting to get at your code, but none
       can definitively conceal it (this is true of every
       language, not just Perl).

       If you're concerned about people profiting from your code,
       then the bottom line is that nothing but a restrictive
       licence will give you legal security.  License your
       software and pepper it with threatening statements like
       ``This is unpublished proprietary software of XYZ Corp.
       Your access to it does not give you permission to use it
       blah blah blah.''  We are not lawyers, of course, so you
       should see a lawyer if you want to be sure your licence's
       wording will stand up in court.

       HHooww ccaann II ccoommppiillee mmyy PPeerrll pprrooggrraamm iinnttoo bbyyttee ccooddee oorr CC??

       Malcolm Beattie has written a multifunction backend
       compiler, available from CPAN, that can do both these
       things.  It is included in the perl5.005 release, but is
       still considered experimental.  This means it's fun to
       play with if you're a programmer but not really for people
       looking for turn-key solutions.

       Merely compiling into C does not in and of itself
       guarantee that your code will run very much faster.
       That's because except for lucky cases where a lot of
       native type inferencing is possible, the normal Perl run
       time system is still present and so your program will take
       just as long to run and be just as big.  Most programs
       save little more than compilation time, leaving execution
       no more than 10-30% faster.  A few rare programs actually
       benefit significantly (like several times faster), but
       this takes some tweaking of your code.

       You'll probably be astonished to learn that the current
       version of the compiler generates a compiled form of your
       script whose executable is just as big as the original
       perl executable, and then some.  That's because as
       currently written, all programs are prepared for a full
       eval() statement.  You can tremendously reduce this cost
       by building a shared libperl.so library and linking
       against that.  See the INSTALL podfile in the perl source
       distribution for details.  If you link your main perl
       binary with this, it will make it miniscule.  For example,
       on one author's system, /usr/bin/perl is only 11k in size!

       In general, the compiler will do nothing to make a Perl
       program smaller, faster, more portable, or more secure.
       In fact, it will usually hurt all of those.  The
       executable will be bigger, your VM system may take longer
       to load the whole thing, the binary is fragile and hard to
       fix, and compilation never stopped software piracy in the
       form of crackers, viruses, or bootleggers.  The real
       advantage of the compiler is merely packaging, and once
       you see the size of what it makes (well, unless you use a
       shared libperl.so), you'll probably want a complete Perl
       install anyway.

       HHooww ccaann II ccoommppiillee PPeerrll iinnttoo JJaavvaa??

       You can't.  Not yet, anyway.  You can integrate Java and
       Perl with the Perl Resource Kit from O'Reilly and
       Associates.  See http://www.oreilly.com/catalog/prkunix/
       for more information.  The Java interface will be
       supported in the core 5.006 release of Perl.

       HHooww ccaann II ggeett ##!!ppeerrll to work on [MS-DOS,NT,...]?

       For OS/2 just use

           extproc perl -S -your_switches

       as the first line in *.cmd file (-S due to a bug in
       cmd.exe's `extproc' handling).  For DOS one should first
       invent a corresponding batch file, and codify it in
       ALTERNATIVE_SHEBANG (see the INSTALL file in the source
       distribution for more information).

       The Win95/NT installation, when using the ActiveState port
       of Perl, will modify the Registry to associate the .pl
       extension with the perl interpreter.  If you install
       another port (Gurusamy Sarathy's is the recommended
       Win95/NT port), or (eventually) build your own Win95/NT
       Perl using a Windows port of gcc (e.g., with cygwin32 or
       mingw32), then you'll have to modify the Registry
       yourself.  In addition to associating .pl with the
       interpreter, NT people can use: SET PATHEXT=%PATHEXT%;.PL
       to let them run the program install-linux.pl merely by
       typing install-linux.

       Macintosh perl scripts will have the appropriate Creator
       and Type, so that double-clicking them will invoke the
       perl application.

       IMPORTANT!: Whatever you do, PLEASE don't get frustrated,
       and just throw the perl interpreter into your cgi-bin
       directory, in order to get your scripts working for a web
       server.  This is an EXTREMELY big security risk.  Take the
       time to figure out how to do it correctly.

       CCaann II wwrriittee uusseeffuull ppeerrll pprrooggrraammss oonn tthhee ccoommmmaanndd lliinnee??

       Yes.  Read the perlrun manpage for more information.  Some
       examples follow.  (These assume standard Unix shell
       quoting rules.)

           # sum first and last fields
           perl -lane 'print $F[0] + $F[-1]' *

           # identify text files
           perl -le 'for(@ARGV) {print if -f && -T _}' *

           # remove (most) comments from C program
           perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c

           # make file a month younger than today, defeating reaper daemons
           perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *

           # find first unused uid
           perl -le '$i++ while getpwuid($i); print $i'

           # display reasonable manpath
           echo $PATH | perl -nl -072 -e '
               s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'

       Ok, the last one was actually an obfuscated perl entry.
       :-)

       WWhhyy ddoonn''tt ppeerrll oonnee--lliinneerrss wwoorrkk oonn mmyy DDOOSS//MMaacc//VVMMSS ssyysstteemm??

       The problem is usually that the command interpreters on
       those systems have rather different ideas about quoting
       than the Unix shells under which the one-liners were
       created.  On some systems, you may have to change single-
       quotes to double ones, which you must NOT do on Unix or
       Plan9 systems.  You might also have to change a single %
       to a %%.

       For example:

           # Unix
           perl -e 'print "Hello world\n"'

           # DOS, etc.
           perl -e "print \"Hello world\n\""

           # Mac
           print "Hello world\n"
            (then Run "Myscript" or Shift-Command-R)

           # VMS
           perl -e "print ""Hello world\n"""

       The problem is that none of this is reliable: it depends
       on the command interpreter.  Under Unix, the first two
       often work. Under DOS, it's entirely possible neither
       works.  If 4DOS was the command shell, you'd probably have
       better luck like this:

         perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""

       Under the Mac, it depends which environment you are using.
       The MacPerl shell, or MPW, is much like Unix shells in its
       support for several quoting variants, except that it makes
       free use of the Mac's non-ASCII characters as control
       characters.

       Using qq(), q(), and qx(), instead of "double quotes",
       'single quotes', and `backticks`, may make one-liners
       easier to write.

       There is no general solution to all of this.  It is a
       mess, pure and simple.  Sucks to be away from Unix, huh?
       :-)

       [Some of this answer was contributed by Kenneth
       Albanowski.]

       WWhheerree ccaann II lleeaarrnn aabboouutt CCGGII oorr WWeebb pprrooggrraammmmiinngg iinn PPeerrll??

       For modules, get the CGI or LWP modules from CPAN.  For
       textbooks, see the two especially dedicated to web stuff
       in the question on books.  For problems and questions
       related to the web, like ``Why do I get 500 Errors'' or
       ``Why doesn't it run from the browser right when it runs
       fine on the command line'', see these sources:

           WWW Security FAQ
               http://www.w3.org/Security/Faq/

           Web FAQ
               http://www.boutell.com/faq/

           CGI FAQ
                       http://www.webthing.com/tutorials/cgifaq.html

           HTTP Spec
               http://www.w3.org/pub/WWW/Protocols/HTTP/

           HTML Spec
               http://www.w3.org/TR/REC-html40/
               http://www.w3.org/pub/WWW/MarkUp/

           CGI Spec
               http://www.w3.org/CGI/

           CGI Security FAQ
               http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt

       Also take a look at the perlfaq9 manpage

       WWhheerree ccaann II lleeaarrnn aabboouutt oobbjjeecctt--oorriieenntteedd PPeerrll pprrooggrraammmmiinngg??

       the perltoot manpage is a good place to start, and you can
       use the perlobj manpage and the perlbot manpage for
       reference.  Perltoot didn't come out until the 5.004
       release, but you can get a copy (in pod, html, or
       postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .

       WWhheerree ccaann II lleeaarrnn aabboouutt lliinnkkiinngg CC wwiitthh PPeerrll?? [[hh22xxss,,
       xxssuubbpppp]]

       If you want to call C from Perl, start with the perlxstut
       manpage, moving on to the perlxs manpage, the xsubpp
       manpage, and the perlguts manpage.  If you want to call
       Perl from C, then read the perlembed manpage, the perlcall
       manpage, and the perlguts manpage.  Don't forget that you
       can learn a lot from looking at how the authors of
       existing extension modules wrote their code and solved
       their problems.

       II''vvee rreeaadd ppeerrlleemmbbeedd,, ppeerrllgguuttss,, eettcc..,, bbuutt II ccaann''tt eemmbbeedd
       ppeerrll iinn mmyy CC pprrooggrraamm,, wwhhaatt aamm II ddooiinngg wwrroonngg??

       Download the ExtUtils::Embed kit from CPAN and run `make
       test'.  If the tests pass, read the pods again and again
       and again.  If they fail, see the perlbug manpage and send
       a bugreport with the output of make test TEST_VERBOSE=1
       along with perl -V.

       WWhheenn II ttrriieedd ttoo rruunn mmyy ssccrriipptt,, II ggoott tthhiiss mmeessssaaggee.. WWhhaatt
       ddooeess iitt mmeeaann??

       the perldiag manpage has a complete list of perl's error
       messages and warnings, with explanatory text.  You can
       also use the splain program (distributed with perl) to
       explain the error messages:

           perl program 2>diag.out
           splain [-v] [-p] diag.out

       or change your program to explain the messages for you:

           use diagnostics;

       or

           use diagnostics -verbose;

       WWhhaatt''ss MMaakkeeMMaakkeerr??

       This module (part of the standard perl distribution) is
       designed to write a Makefile for an extension module from
       a Makefile.PL.  For more information, see the
       ExtUtils::MakeMaker manpage.

AAUUTTHHOORR AANNDD CCOOPPYYRRIIGGHHTT
       Copyright (c) 1997-1999 Tom Christiansen and Nathan
       Torkington.  All rights reserved.

       When included as an integrated part of the Standard
       Distribution of Perl or of its documentation (printed or
       otherwise), this work is covered under Perl's Artistic
       Licence.  For separate distributions of all or part of
       this FAQ outside of that, see the perlfaq manpage.

       Irrespective of its distribution, all code examples here
       are public domain.  You are permitted and encouraged to
       use this code and any derivatives thereof in your own
       programs for fun or for profit as you see fit.  A simple
       comment in the code giving credit to the FAQ would be
       courteous but is not required.

27/Mar/1999            perl 5.005, patch 03                     1