perlfaq.pod

source of perl for linux application,

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/vperl.html) 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

=over 4

=item Bash

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

=item 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/)

=item Tcsh

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

=item Zsh

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

=back

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 limit).

=over 4

=item BBEdit and BBEdit Lite

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

=item Alpha

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/).

=back

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

=head2 Where can I get Perl macros for vi?

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.  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.perl.com/CPAN/src/misc.

=head2 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 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 C<"main'foo">
(single quote), and mess up the indentation and highlighting.  You
are probably using C<"main::foo"> in new Perl code anyway, so this
shouldn't be an issue.

=head2 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.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
this program repeats a command and updates the screen as needed, rendering
B<rep ps axu> similar to B<top>.

=head2 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.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/%7Epvhp/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/%7Eamundson/perl/perltk/toc.html .

=head2 How can I generate simple menus without using CGI or Tk?

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

=head2 What is undump?

See the next question on ``How can I make my Perl program run faster?''

=head2 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.

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).

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 I<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 F<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 F<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.

=head2 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 F<INSTALL> file in the source
distribution.  You can find out whether you are using perl's malloc by
typing C<perl -V:usemymalloc>.

=head2 Is it unsafe to return a pointer to local data?

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";

=head2 How can I free an array or hash so my program shrinks?

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, C<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 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.

=head2 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 B<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.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 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.

=head2 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''.