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NAME    [Toc]    [Back]

       perlfaq3 - Programming Tools ($Revision: 1.7 $, $Date:
       2004/04/07 21:33:08 $)

DESCRIPTION    [Toc]    [Back]

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

       How do I do (anything)?

       Have you looked at CPAN (see perlfaq2)?  The chances are
       that someone has already written a module that can solve
       your problem.  Have you read the appropriate manpages?
       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
               Regexes         perlre, perlfunc, perlop,  perllocale
               Moving to perl5 perltrap, perl
               Linking   w/C       perlxstut,  perlxs,  perlcall,
perlguts, perlembed
               Various              http://www.cpan.org/misc/old-
                               (not  a man-page but still useful,
a collection
                                of various essays on  Perl  techniques)

       A crude table of contents for the Perl manpage set is
       found in perltoc.

       How can I use Perl interactively?

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

           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

       Is there a Perl shell?

       The psh (Perl sh) is currently at version 1.8. The Perl
       Shell is a shell that combines the interactive nature of a
       Unix shell with the power of Perl. The goal is a full featured
 shell that behaves as expected for normal shell
       activity and uses Perl syntax and functionality for control-flow
 statements and other things.  You can get psh at
       http://www.focusresearch.com/gregor/psh/ .
       Zoidberg is a similar project and provides a shell written
       in perl, configured in perl and operated in perl. It is
       intended as a login shell and development environment. It
       can be found at http://zoidberg.sf.net/ or your local CPAN

       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.

       How do I find which modules are installed on my system?

       You can use the ExtUtils::Installed module to show all
       installed distributions, although it can take awhile to do
       its magic.  The standard library which comes with Perl
       just shows up as "Perl" (although you can get those with

               use ExtUtils::Installed;

               my $inst    = ExtUtils::Installed->new();
               my @modules = $inst->modules();

       If you want a list of all of the Perl module filenames,
       you can use File::Find::Rule.

               use File::Find::Rule;

               my @files = File::Find::Rule->file()->name( '*.pm'
)->in( @INC );

       If you do not have that module, you can do the same thing
       with File::Find which is part of the standard library.

           use File::Find;
           my @files;

           find sub { push @files, $File::Find::name if -f  _  &&
/.pm$/ },

               print join "0, @files;

       If you simply need to quickly check to see if a module is
       available, you can check for its documentation.  If you
       can read the documentation the module is most likely
       installed.  If you cannot read the documentation, the module
 might not have any (in rare cases).

               prompt% perldoc Module::Name

       You can also try to include the module in a one-liner to
       see if perl finds it.

               perl -MModule::Name -e1
       How do I debug my Perl programs?

       Have you tried "use warnings" or used "-w"?  They enable
       warnings to detect 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",
       "our", or "use vars".

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

         open(FH, "> /etc/cantwrite")
           or die "Couldn't write to /etc/cantwrite: $!0;

       Did you read perltrap?  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 perldebug?
       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.

       How do I profile my Perl programs?

       You should get the Devel::DProf module from the standard
       distribution (or separately on CPAN) and also use Benchmark.pm
 from the standard distribution.  The Benchmark
       module 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;
                                  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 proves little about
       the differing complexities of contrasting algorithms.

       How do I cross-reference my Perl programs?

       The B::Xref module can be used to generate cross-reference
       reports for Perl programs.

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

       Is there a pretty-printer (formatter) for Perl?

       Perltidy is a Perl script which indents and reformats Perl
       scripts to make them easier to read by trying to follow
       the rules of the perlstyle. If you write Perl scripts, or
       spend much time reading them, you will probably find it
       useful.  It is available at http://perltidy.source-

       Of course, if you simply follow the guidelines in perlstyle,
 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 perlmode
 or newer cperl-mode for emacs can provide remarkable
       amounts of help with most (but not all) code, and even
       less programmable editors can provide significant assistance.
  Tom Christiansen and many other VI users  swear by
       the following settings in vi and its clones:

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

       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.  A more complete example,
       with comments, can be found at

       The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz
 does lots of things related
       to generating nicely printed output of documents, as does
       enscript at http://people.ssh.fi/mtr/genscript/ .
       Is there a ctags for Perl?

       Recent versions of ctags do much more than older versions
       did.  EXUBERANT CTAGS is available from
       http://ctags.sourceforge.net/ and does a good job of making
 tags files for perl code.

       There is also a simple one at
       http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which
       may do the trick.  It can be easy to hack this into what
       you want.

       Is there an IDE or Windows Perl Editor?

       Perl  programs are just plain text, so any editor will do.

       If you're on Unix, you already have an IDE--Unix itself.
       The UNIX philosophy is the philosophy of several small
       tools that each do one thing and do it well.  It's like a
       carpenter's toolbox.

       If you want an IDE, check the following:

           ActiveState's cross-platform (as of April 2001 Windows
           and Linux), multi-language IDE has Perl support,
           including a regular expression debugger and remote
           debugging ( http://www.ActiveState.com/Prod-
           ucts/Komodo/index.html ).  (Visual Perl, a Visual Studio.NET
 plug-in is currently (early 2001) in beta (
           alPerl/index.html )).

       The Object System
           ( http://www.castlelink.co.uk/object_system/ ) is a
           Perl web applications development IDE, apparently for
           any platform that runs Perl.

       Open Perl IDE
           ( http://open-perl-ide.sourceforge.net/ ) Open Perl
           IDE is an integrated development environment for writing
 and debugging Perl scripts with ActiveState's
           ActivePerl distribution under Windows 95/98/NT/2000.

           ( http://www.solutionsoft.com/perl.htm ) is an integrated
 development environment for Windows that supports
 Perl development.

           ( http://helpconsulting.net/visiperl/ ) From Help Consulting,
 for Windows.
           ( http://www.optiperl.com/ ) is a Windows IDE with
           simulated CGI environment, including debugger and syntax
 highlighting editor.

       For editors: if you're on Unix you probably have vi or a
       vi clone already, and possibly an emacs too, so you may
       not need to download anything.  In any emacs the cperlmode
 (M-x cperl-mode) gives you perhaps the best available
       Perl editing mode in any editor.

       If you are using Windows, you can use any editor that lets
       you work with plain text, such as NotePad or WordPad.
       Word processors, such as Microsoft Word or WordPerfect,
       typically do not work since they insert all sorts of
       behind-the-scenes information, although some allow you to
       save files as "Text Only". You can also download text editors
 designed specifically for programming, such as
       Textpad ( http://www.textpad.com/ ) and UltraEdit (
       http://www.ultraedit.com/ ), among others.

       If you are using MacOS, the same concerns apply.  MacPerl
       (for Classic environments) comes with a simple editor.
       Popular external editors are BBEdit ( http://www.bbe-
       dit.com/ ) or Alpha ( http://www.kelehers.org/alpha/ ).
       MacOS X users can use Unix editors as well.

       GNU Emacs



       Jed http://space.mit.edu/~davis/jed/

       or a vi clone such as



       Vim http://www.vim.org/

       For vi lovers in general, Windows or elsewhere:


       nvi ( http://www.bostic.com/vi/ , available from CPAN in
       src/misc/) is yet another vi clone, unfortunately not
       available for Windows, but in UNIX platforms you might be
       interested in trying it out, firstly because strictly
       speaking it is not a vi clone, it is the real vi, or the
       new incarnation of it, and secondly because you can embed
       Perl inside it to use Perl as the scripting language.  nvi
       is not alone in this, though: at least also vim and vile
       offer an embedded Perl.

       The following are Win32 multilanguage editor/IDESs that
       support Perl:




       There is also a toyedit Text widget based editor written
       in Perl that is distributed with the Tk module on CPAN.
       The ptkdb ( http://world.std.com/~aep/ptkdb/ ) is a
       Perl/tk based debugger that acts as a development environment
 of sorts.  Perl Composer ( http://perlcomposer.sourceforge.net/
 ) is an IDE for Perl/Tk GUI creation.

       In addition to an editor/IDE you might be interested in a
       more powerful shell environment for Win32.  Your options

           from the Cygwin package ( http://sources.red-
           hat.com/cygwin/ )

       Ksh from the MKS Toolkit ( http://www.mks.com/ ), or the
           Bourne shell of the U/WIN environment (
           http://www.research.att.com/sw/tools/uwin/ )

           ftp://ftp.astron.com/pub/tcsh/ , see also

       Zsh ftp://ftp.blarg.net/users/amol/zsh/ , see also

       MKS and U/WIN are commercial (U/WIN is free for educational
 and research purposes), Cygwin is covered by the
       GNU Public License (but that shouldn't matter for Perl
       use).  The Cygwin, MKS, and U/WIN all contain (in addition
       to the shells) a comprehensive set of standard UNIX
       toolkit utilities.
       If you're transferring text files between Unix and Windows
       using FTP be sure to transfer them in ASCII mode so the
       ends of lines are appropriately converted.

       On Mac OS the MacPerl Application comes with a simple 32k
       text editor that behaves like a rudimentary IDE.  In contrast
 to the MacPerl Application the MPW Perl tool can
       make use of the MPW Shell itself as an editor (with no 32k

       BBEdit and BBEdit Lite
           are text editors for Mac OS that have a Perl sensitivity
 mode ( http://web.barebones.com/ ).

           is an editor, written and extensible in Tcl, that
           nonetheless has built in support for several popular
           markup and programming languages including Perl and
           HTML ( http://alpha.olm.net/ ).

       Pepper and Pe are programming language sensitive text editors
 for Mac OS X and BeOS respectively (
       http://www.hekkelman.com/ ).

       Where can I get Perl macros for vi?

       For a complete version of Tom Christiansen's vi configuration
 file, see http://www.cpan.org/authors/Tom_Chris-
       tiansen/scripts/toms.exrc.gz , the standard benchmark file
       for vi emulators.  The file 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.cpan.org/src/misc/ .

       Where can I get perl-mode for emacs?

       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

       In the Perl source directory, you'll find a directory
       called "emacs", which contains a cperl-mode that colorcodes
 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
       highlighting.  You are probably using "main::foo" in new
       Perl code anyway, so this shouldn't be an issue.
       How can I use curses with Perl?

       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
       tiansen/scripts/rep.gz ; this program repeats a command
       and updates the screen as needed, rendering rep ps axu
       similar to top.

       How can I use X or Tk with Perl?

       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

       Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
       http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the
       Perl/Tk Reference Guide available at
       http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
       online manpages at http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html

       How can I generate simple menus without using CGI or Tk?

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

       How can I make my Perl program run faster?

       The best way to do this is to come up with a better algorithm.
  This can often make a dramatic difference.  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.
  You will probably want to read the answer to the
       earlier question ``How do I profile my Perl programs?'' if
       you haven't done so already.

       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, modules that have
       critical sections can be written in C (for instance, the
       PDL module from CPAN).
       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

       The undump program was an ancient attempt to speed up 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.

       How can I make my Perl program take less memory?

       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--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".

       Of course, the best way to save memory is to not do anything
 to waste it in the first place. Good programming
       practices can go a long way toward this:

       * Don't slurp!
           Don't read an entire file into memory if you can process
 it line by line. Or more concretely, use a loop
           like this:
                   # Good Idea
                   while (<FILE>) {
                      # ...

           instead of this:

                   # Bad Idea
                   @data = <FILE>;
                   foreach (@data) {
                       # ...

           When the files you're processing are small, it doesn't
           much matter which way you do it, but it makes a huge
           difference when they start getting larger.

       * Use map and grep selectively
           Remember that both map and grep expect a LIST argument,
 so doing this:

                   @wanted = grep {/pattern/} <FILE>;

           will cause the entire file to be slurped. For large
           files, it's better to loop:

                   while (<FILE>) {
                           push(@wanted, $_) if /pattern/;

       * Avoid unnecessary quotes and stringification
           Don't quote large strings unless absolutely necessary:

                   my $copy = "$large_string";

           makes 2 copies of $large_string (one for $copy and
           another for the quotes), whereas

                   my $copy = $large_string;

           only makes one copy.

           Ditto for stringifying large arrays:

                           local $, = "0;
                           print @big_array;

           is much more memory-efficient than either
                   print join "0, @big_array;


                           local $" = "0;
                           print "@big_array";

       * Pass by reference
           Pass arrays and hashes by reference, not by value. For
           one thing, it's the only way to pass multiple lists or
           hashes (or both) in a single call/return. It also
           avoids creating a copy of all the contents. This
           requires some judgment, however, because any changes
           will be propagated back to the original data. If you
           really want to mangle (er, modify) a copy, you'll have
           to sacrifice the memory needed to make one.

       * Tie large variables to disk.
           For "big" data stores (i.e. ones that exceed available
           memory) consider using one of the DB modules to store
           it on disk instead of in RAM. This will incur a
           penalty in access time, but that's probably better
           than causing your hard disk to thrash due to massive

       Is it safe to return a reference to local or lexical data?

       Yes. Perl's garbage collection system takes care of this
       so everything works out right.

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

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

           print $many[4][5], "0;

           print "@many0;

       How can I free an array or hash so my program shrinks?

       You usually 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, systems that use
       mmap(2) for allocating large chunks of memory) can reclaim
       memory that is no longer used, but on such systems, perl
       must be configured and compiled to use the OS's malloc,
       not perl's.

       However, judicious use of my() on your variables will help
       make sure that they go out of scope so that Perl can free
       up that space 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.

       How can I make my CGI script more efficient?

       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 isn't going to
       help you 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 programs 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 programs, so
       investigate them with care.

       See http://www.cpan.org/modules/by-cate-
       gory/15_World_Wide_Web_HTML_HTTP_CGI/ .

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

       How can I hide the source for my Perl program?

       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

       You can try using encryption via source filters (Starting
       from Perl 5.8 the Filter::Simple and Filter::Util::Call
       modules are included in the standard distribution), 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
       (true of every language, not just Perl).

       It is very easy to recover the source of Perl programs.
       You simply feed the program to the perl interpreter and
       use the modules in the B:: hierarchy.  The B::Deparse module
 should be able to defeat most attempts to hide source.
       Again, this is not unique to Perl.

       If you're concerned about people profiting from your code,
       then the bottom line is that nothing but a restrictive
       license 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 license's wording
       will stand up in court.

       How can I compile my Perl program into byte code or C?

       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
 (even running 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 minuscule.  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 can make your situation worse.  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

       How can I compile Perl into Java?

       You can also integrate Java and Perl with the Perl
       Resource Kit from O'Reilly and Associates.  See
       http://www.oreilly.com/catalog/prkunix/ .

       Perl 5.6 comes with Java Perl Lingo, or JPL.  JPL, still
       in development, allows Perl code to be called from Java.
       See jpl/README in the Perl source tree.

       How can I get "#!perl" 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 "ALTERNATE_SHEBANG"
 (see the dosish.h 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, perhaps even building your own Win95/NT Perl
       from the standard sources by using a Windows port of gcc
       (e.g., with cygwin 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 programs 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 programs working for a web
       server.  This is an EXTREMELY big security risk.  Take the
       time to figure out how to do it correctly.

       Can I write useful Perl programs on the command line?

       Yes.  Read perlrun 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 '

       OK, the last one was actually an Obfuscated Perl Contest
       entry. :-)

       Why don't Perl one-liners work on my DOS/Mac/VMS system?

       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 singlequotes
 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 world0'

           # DOS, etc.
           perl -e "print

           # Mac
           print "Hello world0
            (then Run "Myscript" or Shift-Command-R)

           # MPW
           perl -e 'print "Hello world0'

           # VMS
           perl -e "print ""Hello world0""

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

         perl -e "print <Ctrl-x>"Hello world0Ctrl-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

       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

       [Some of this answer was contributed by Kenneth

       Where can I learn about CGI or Web programming in Perl?

       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 the troubleshooting guides
       and references in perlfaq9 or in the CGI MetaFAQ:


       Where  can I learn about object-oriented Perl programming?

       A good place to start is perltoot, and you can use perlobj,
 perlboot, perltoot, perltooc, and perlbot for reference.
  (If you are using really old Perl, you may not have
       all of these, try http://www.perldoc.com/ , but consider
       upgrading your perl.)

       A good book on OO on Perl is the "Object-Oriented Perl" by
       Damian Conway from Manning Publications, http://www.man-

       Where can I learn about linking C with Perl? [h2xs,

       If you want to call C from Perl, start with perlxstut,
       moving on to perlxs, xsubpp, and perlguts.  If you want to
       call Perl from C, then read perlembed, perlcall, and
       perlguts.  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.

       I've read perlembed, perlguts, etc., but I can't embed
       perl in my C program; what am I doing wrong?

       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 perlbug and send a bug
       report with the output of "make test TEST_VERBOSE=1" along
       with "perl -V".

       When I tried to run my script, I got this message. What
       does it mean?

       A complete list of Perl's error messages and warnings with
       explanatory text can be found in perldiag. 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;


           use diagnostics -verbose;

       What's MakeMaker?

       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 ExtUtils::MakeMaker.


       Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
  All rights reserved.

       This documentation is free; you can redistribute it and/or
       modify it under the same terms as Perl itself.

       Irrespective of its distribution, all code examples here
       are in the 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.

perl v5.8.5                 2002-11-06                         19
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