Unix/Linux Go Back    

RedHat 9 (Linux i386) - man page for perlfaq3 (redhat section 1)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)

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

       perlfaq3 - Programming Tools ($Revision: 1.29 $, $Date: 2002/11/13 06:23:50 $)

       This section of the FAQ answers questions related to programmer tools and programming sup-

       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/olddoc/FMTEYEWTK.tgz
			       (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 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.

       Is there a Perl shell?

       In general, not yet.  There is psh available at


       Which includes the following description:

	   The Perl Shell is a shell that combines the interactive nature
	   of a Unix shell with the power of Perl. The goal is to eventually
	   have a full featured shell that behaves as expected for normal
	   shell activity. But, the Perl Shell will use Perl syntax and
	   functionality for control-flow statements and other things.

       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 Mod::CoreList).

	       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 "\n", @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 prac-

       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: $!\n";

       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 pro-
       gram and see what it's doing and thus work out why what it's doing isn't what it should be

       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;
				  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 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

       Of course, if you simply follow the guidelines in perlstyle, you shouldn't need to refor-
       mat.  The habit of formatting your code as you write it will help prevent bugs.	Your edi-
       tor can and should help you with this.  The perl-mode or newer cperl-mode for emacs can
       provide remarkable amounts of help with most (but not all) code, and even less program-
       mable 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://peo-
       ple.ssh.fi/mtr/genscript/ .

       Is there a ctags for Perl?

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

       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 phi-
       losophy of several small tools that each do one thing and do it well.  It's like a carpen-
       ter'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/Products/Komodo/index.html ).  (Visual Perl, a Visual Stu-
	   dio.NET plug-in is currently (early 2001) in beta ( http://www.ActiveState.com/Prod-
	   ucts/VisualPerl/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 dis-
	   tribution 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, includ-
	   ing 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 cperl-mode (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.bbedit.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

	   ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/


       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 inter-
       ested 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://perlcom-
       poser.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 include

	   from the Cygwin package ( http://sources.redhat.com/cygwin/ )

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

	   ftp://ftp.astron.com/pub/tcsh/ , see also http://www.primate.wisc.edu/soft-

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

       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 Cyg-
       win, MKS, and U/WIN all contain (in addition to the shells) a comprehensive set of stan-
       dard 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 limit).

       BBEdit and BBEdit Lite
	   are text editors for Mac OS that have a Perl sensitivity mode ( http://web.bare-
	   bones.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_Christiansen/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 sup-
       port for the Perl debugger built in.  These should come with the standard Emacs 19 distri-

       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

       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
       http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ; this program repeats a com-
       mand 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 http://www.cpan.org/modules/by-cate-

       Invaluable for Perl/Tk programming are the Perl/Tk FAQ at http://w4.lns.cor-
       nell.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/perlmenu.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 dra-
       matic 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 bottle-
       neck 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).

       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 some-
       times 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 I/O intensive applications).	To try this, see the INSTALL file in the source
       distribution, especially the ``Selecting File I/O 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.

       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 work-
       ing 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

       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:

       o Don't slurp!
	   Don't read an entire file into memory if you can process it line by line. Or more con-
	   cretely, 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.

       o 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/;

       o 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 $, = "\n";
			   print @big_array;

	   is much more memory-efficient than either

		   print join "\n", @big_array;


			   local $" = "\n";
			   print "@big_array";

       o 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 creat-
	   ing 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.

       o 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 swapping.

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

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

	   print "@many\n";

       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 con-
       figured 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 automati-
       cally 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 wor-
       rying about much in Perl, but even this capability (preallocation of data types) is in the

       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

       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-category/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 func-
       tional 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

       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 view-
       ing the source.	Security through obscurity, the name for hiding your bugs instead of fix-
       ing them, is little security indeed.

       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 dis-
       assemble 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 consid-
       ered 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 compila-
       tion 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 exe-
       cutable, 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 por-
       table, 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 prob-
       ably want a complete Perl install anyway.

       How can I compile Perl into Java?

       You can also integrate Java and Perl with the Perl Resource Kit from O'Reilly and Asso-
       ciates.	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 "ALTERNA-
       TIVE_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 Reg-
       istry 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 Reg-
       istry 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 typ-
       ing "install-linux".

       Macintosh Perl programs will have the appropriate Creator and Type, so that double-click-
       ing them will invoke the Perl application.

       IMPORTANT!: Whatever you do, PLEASE don't get frustrated, and just throw the perl inter-
       preter 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

       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 differ-
       ent 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)

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

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

       The problem is that none of these examples are reliable: they depend on the command inter-
       preter.	Under Unix, the first two often work. Under DOS, it's entirely possible that nei-
       ther 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.

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

       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 Pub-
       lications, http://www.manning.com/Conway/index.html

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

       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 exten-
       sion 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 pro-
       grams 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 v5.8.0				    2003-02-18				      PERLFAQ3(1)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums

All times are GMT -4. The time now is 02:33 AM.