perlfaqo.txt

source of perl for linux application,

NAME
perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $)
DESCRIPTION
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 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
        Regexes         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)
A crude table of contents for the Perl man page set is found in perltoc.
How can I use Perl interactively?
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.
Is there a Perl shell?
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.
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: $!\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 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;
                           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, 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
Is there a pretty-printer (formatter) for Perl?
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 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 perl-mode 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 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/%7Edemaille/a2ps/ does lots of things related to generating nicely printed output of documents.
Is there a ctags for Perl?
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.
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 a Windows IDE, check the following:
CodeMagicCD
http://www.codemagiccd.com/
Komodo
ActiveState's cross-platform, 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 Studio.NET plug-in is currently (early 2001) in beta (http://www.ActiveState.com/Products/VisualPerl/index.html)).
The Object System
(http://www.castlelink.co.uk/object_system/) is a Perl web applications development IDE.
PerlBuilder
(http://www.solutionsoft.com/perl.htm) is an integrated development environment for Windows that supports Perl development.
Perl code magic
(http://www.petes-place.com/codemagic.html).
visiPerl+
http://helpconsulting.net/visiperl/, from Help Consulting.
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.
For Windows editors: you can download an Emacs
GNU Emacs
http://www.gnu.org/software/emacs/windows/ntemacs.html
MicroEMACS
http://members.nbci.com/uemacs/
XEmacs
http://www.xemacs.org/Download/index.html
or a vi clone such as
Elvis
ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
Vile
http://vile.cx/
Vim
http://www.vim.org/
win32: http://www.cs.vu.nl/%7Etmgil/vi.html
For vi lovers in general, Windows or elsewhere: http://www.thomer.com/thomer/vi/vi.html.
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:
Codewright
http://www.starbase.com/
MultiEdit
http://www.MultiEdit.com/
SlickEdit
http://www.slickedit.com/
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
Bash
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 environment (http://www.research.att.com/sw/tools/uwin/)
Tcsh
ftp://ftp.astron.com/pub/tcsh/, see also http://www.primate.wisc.edu/software/csh-tcsh-book/
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 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).
BBEdit and BBEdit Lite
are text editors for Mac OS that have a Perl sensitivity mode (http://web.barebones.com/).
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/).
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.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.
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 "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.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; this program repeats a command and updates the screen as needed, rendering rep ps axu similar to top.