Manual Pages for UNIX Darwin command on man perlfaq3

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

NAME

perlfaq3 - Programming Tools ($Revision: 1.41 $, $Date: 2004/11/03

22:45:32 $)

DESCRIPTION

This section of the FAQ answers questions related to programmer tools and programming support. HHooww ddoo II ddoo ((aannyytthhiinngg))?? Have you looked at CPAN (see 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. HHooww ccaann II uussee PPeerrll iinntteerraaccttiivveellyy??

The typical approach uses the Perl debugger, described in the perlde-

bug(1) manpage, on an ``empty'' program, like this:

perl -de 42

Now just type in any legal Perl code, and it will be immediately evalu-

ated. You can also examine the symbol table, get stack backtraces, check variable values, set breakpoints, and other operations typically found in symbolic debuggers. IIss tthheerree aa PPeerrll sshheellll?? 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 functional-

ity 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://zoid-

berg.sf.net/ or your local CPAN mirror. The Shell.pm module (distributed with Perl) makes Perl try commands which aren't part of the Perl language as shell commands. perlsh from the source distribution is simplistic and uninteresting, but may still be what you want. HHooww ddoo II ffiinndd wwhhiicchh mmoodduulleess aarree iinnssttaalllleedd oonn mmyy ssyysstteemm??

You can use the ExtUtils::Installed module to show all installed dis-

tributions, 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 Module::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, $File::Find::name if -f && /\.pm$/ },

@INC; 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 documenta-

tion, 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

HHooww ddoo II ddeebbuugg mmyy PPeerrll pprrooggrraammss??

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 ref-

erences, 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 pro-

grammers 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. HHooww ddoo II pprrooffiillee mmyy PPeerrll pprrooggrraammss?? 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 = 10000;

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.

HHooww ddoo II ccrroossss-rreeffeerreennccee mmyy PPeerrll pprrooggrraammss??

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

Perl programs.

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

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

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 perl-

style. If you write Perl scripts, or spend much time reading them, you will probably find it useful. It is available at http://perltidy.sourceforge.net 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 Chris-

tiansen 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 con-

trol 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 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz

The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does

lots of things related to generating nicely printed output of docu-

ments, as does enscript at http://people.ssh.fi/mtr/genscript/ . IIss tthheerree aa ccttaaggss ffoorr PPeerrll??

Recent versions of ctags do much more than older versions did. EXUBER-

ANT 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. IIss tthheerree aann IIDDEE oorr WWiinnddoowwss PPeerrll EEddiittoorr?? 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 phi-

losophy 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 (in alphabetical order, not order of preference): Eclipse

The Eclipse Perl Integration Project integrates Perl editing/debug-

ging with Eclipse.

The website for the project is http://e-p-i-c.sf.net/

Komodo

ActiveState's cross-platform (as of October 2004, that's Windows,

Linux, and Solaris), multi-language IDE has Perl support, including

a regular expression debugger and remote debugging ( http://www.ActiveState.com/Products/Komodo/ ). Open Perl IDE

( http://open-perl-ide.sourceforge.net/ ) Open Perl IDE is an inte-

grated development environment for writing and debugging Perl scripts with ActiveState's ActivePerl distribution under Windows 95/98/NT/2000. OptiPerl ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI environment, including debugger and syntax highlighting editor. PerlBuilder

( http://www.solutionsoft.com/perl.htm ) is an integrated develop-

ment environment for Windows that supports Perl development. visiPerl+ ( http://helpconsulting.net/visiperl/ ) From Help Consulting, for Windows. Visual Perl ( http://www.activestate.com/Products/VisualPerl/ ) Visual Perl is

a Visual Studio.NET plug-in from ActiveState.

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 per-

haps 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.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use Unix editors as well. GNU Emacs http://www.gnu.org/software/emacs/windows/ntemacs.html MicroEMACS http://www.microemacs.de/ XEmacs http://www.xemacs.org/Download/index.html Jed http://space.mit.edu/~davis/jed/ or a vi clone such as Elvis

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

Vile http://dickey.his.com/vile/vile.html Vim http://www.vim.org/ 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.borland.com/codewright/ 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/ ) is an IDE for Perl/Tk GUI cre-

ation. 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.pri-

mate.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 appropri-

ately 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 Appli-

cation the MPW Perl tool can make use of the MPW Shell itself as an editor (with no 32k limit). Affrus is a full Perl development enivornment with full debugger support ( http://www.latenightsw.com ). Alpha is an editor, written and extensible in Tcl, that nonetheless has

built in support for several popular markup and programming lan-

guages including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ). BBEdit and BBEdit Lite are text editors for Mac OS that have a Perl sensitivity mode ( http://web.barebones.com/ ). Pepper and Pe are programming language sensitive text editors for Mac OS X and BeOS respectively ( http://www.hekkelman.com/ ). WWhheerree ccaann II ggeett PPeerrll mmaaccrrooss ffoorr vvii?? For a complete version of Tom Christiansen's vi configuration file, see http://www.cpan.org/authors/TomChristiansen/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/ .

WWhheerree ccaann II ggeett ppeerrll-mmooddee ffoorr eemmaaccss??

Since Emacs version 19 patchlevel 22 or so, there have been both a

perl-mode.el and support for the Perl debugger built in. These should

come with the standard Emacs 19 distribution. In the Perl source directory, you'll find a directory called "emacs",

which contains a cperl-mode that color-codes keywords, provides con-

text-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. HHooww ccaann II uussee ccuurrsseess wwiitthh PPeerrll??

The Curses module from CPAN provides a dynamically loadable object mod-

ule interface to a curses library. A small demo can be found at the directory http://www.cpan.org/authors/TomChristiansen/scripts/rep.gz ;

this program repeats a command and updates the screen as needed, ren-

dering rreepp ppss aaxxuu similar to ttoopp. HHooww ccaann II uussee XX oorr TTkk wwiitthh PPeerrll??

Tk is a completely Perl-based, object-oriented interface to the Tk

toolkit that doesn't force you to use Tcl just to get at Tk. Sx is an interface to the Athena Widget set. Both are available from CPAN. See

the directory http://www.cpan.org/modules/by-category/08UserInter-

faces/

Invaluable for Perl/Tk programming are the Perl/Tk FAQ at http://pha-

seit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference Guide available at http://www.cpan.org/authors/StephenOLidie/ , and

the online manpages at http://www-users.cs.umn.edu/%7Eamund-

son/perl/perltk/toc.html . HHooww ccaann II ggeenneerraattee ssiimmppllee mmeennuuss wwiitthhoouutt uussiinngg CCGGII oorr TTkk?? The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz module,

which is curses-based, can help with this.

HHooww ccaann II mmaakkee mmyy PPeerrll pprrooggrraamm rruunn ffaasstteerr?? The best way to do this is to come up with a better algorithm. This can often make a dramatic difference. 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 exe-

cutable, but your Perl programs (and programmers) may thank you for it. See the INSTALL file in the source distribution for more information. 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. HHooww ccaann II mmaakkee mmyy PPeerrll pprrooggrraamm ttaakkee lleessss mmeemmoorryy??

When it comes to time-space tradeoffs, Perl nearly always prefers to

throw memory at a problem. Scalars in Perl use more memory than strings in C, arrays take more than that, and hashes use even more. While there's still a lot to be done, recent releases have been addressing these issues. For example, as of 5.004, duplicate hash keys are shared amongst all hashes using them, so require no reallocation. In some cases, using substr() or vec() to simulate arrays can be highly beneficial. For example, an array of a thousand booleans will take at

least 20,000 bytes of space, but it can be turned into one 125-byte bit

vector-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) mod-

ules 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 distribu-

tion. 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 () {

# ...

} instead of this:

# Bad Idea

@data = ; 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/} ; will cause the entire file to be slurped. For large files, it's better to loop: while () {

push(@wanted, $) if /pattern/;

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

my $copy = "$largestring";

makes 2 copies of $largestring (one for $copy and another for the

quotes), whereas

my $copy = $largestring;

only makes one copy. Ditto for stringifying large arrays: {

local $, = "\n";

print @bigarray; }

is much more memory-efficient than either

print join "\n", @bigarray; or {

local $" = "\n";

print "@bigarray"; } * 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 con-

tents. 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) con-

sider 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 swap-

ping. IIss iitt ssaaffee ttoo rreettuurrnn aa rreeffeerreennccee ttoo llooccaall oorr lleexxiiccaall ddaattaa?? 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], "\n";

print "@many\n"; HHooww ccaann II ffrreeee aann aarrrraayy oorr hhaasshh ssoo mmyy pprrooggrraamm sshhrriinnkkss?? 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. HHooww ccaann II mmaakkee mmyy CCGGII ssccrriipptt mmoorree eeffffiicciieenntt?? Beyond the normal measures described to make general Perl programs faster or smaller, a CGI program has additional issues. It may be run several times per second. Given that each time it runs it will need to

be re-compiled and will often allocate a megabyte or more of system

memory, this can be a killer. Compiling into C iissnn''tt ggooiinngg ttoo hheellpp yyoouu

because the process start-up overhead is where the bottleneck is.

There are two popular ways to avoid this overhead. One solution involves running the Apache HTTP server (available from http://www.apache.org/ ) with either of the modperl or modfastcgi plugin modules. With modperl and the Apache::Registry module (distributed with

modperl), 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 any-

thing a module written in C can. For more on modperl, see http://perl.apache.org/ With the FCGI module (from CPAN) and the modfastcgi 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/15WorldWideWebHTMLHTTPCGI/ .

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 per-

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

Delete it. :-) Seriously, there are a number of (mostly unsatisfactory)

solutions with varying levels of ``security''. First of all, however, you can't take away read permission, because the source code has to be readable in order to be compiled and interpreted. (That doesn't mean that a CGI script's source is readable by people on

the web, though-only by people with access to the filesystem.) So you

have to leave the permissions at the socially friendly 0755 level. Some people regard this as a security problem. If your program does insecure things and relies on people not knowing how to exploit those insecurities, it is not secure. It is often possible for someone to determine the insecure things and exploit them without viewing the source. Security through obscurity, the name for hiding your bugs instead of fixing them, is little security indeed. You can try using encryption via source filters (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 crack-

ers might be able to disassemble it. These pose varying degrees of

difficulty to people wanting to get at your code, but none can defini-

tively 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. HHooww ccaann II ccoommppiillee mmyy PPeerrll pprrooggrraamm iinnttoo bbyyttee ccooddee oorr CC?? Malcolm Beattie has written a multifunction backend compiler, available from CPAN, that can do both these things. It is included in the perl5.005 release, but is still considered experimental. This means it's fun to play with if you're a programmer but not really for people

looking for turn-key solutions.

Merely compiling into C does not in and of itself guarantee that your code will run very much faster. That's because except for lucky cases where a lot of native type inferencing is possible, the normal Perl

run-time system is still present and so your program will take just as

long to run and be just as big. Most programs save little more than

compilation time, leaving execution no more than 10-30% faster. A few

rare programs actually benefit significantly (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 anyway. HHooww ccaann II ccoommppiillee PPeerrll iinnttoo JJaavvaa?? You can also integrate Java and Perl with the Perl Resource Kit from O'Reilly Media. See http://www.oreilly.com/catalog/prkunix/ .

Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in develop-

ment, allows Perl code to be called from Java. See jpl/README in the Perl source tree.

HHooww ccaann II ggeett ""##!!ppeerrll"" ttoo wwoorrkk oonn [[MMSS-DDOOSS,,NNTT,,......]]??

For OS/2 just use

extproc perl -S -yourswitches

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 "ALTERNATESHEBANG" (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 Reg-

istry yourself. In addition to associating ".pl" with the interpreter,

NT people can use: "SET PATHEXT=%PATHEXT%;.PL" to let them run the pro-

gram "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 secu-

rity risk. Take the time to figure out how to do it correctly. CCaann II wwrriittee uusseeffuull PPeerrll pprrooggrraammss oonn tthhee ccoommmmaanndd lliinnee?? 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 '

s![^/+]*$!man!&&-d&&!$s{$}++&&push@m,$;END{print"@m"}'

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

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

The problem is usually that the command interpreters on those systems have rather different ideas about quoting than the Unix shells under

which the one-liners were created. On some systems, you may have to

change single-quotes to double ones, which you must NOT do on Unix or

Plan9 systems. You might also have to change a single % to a %%.

For example:

# Unix

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

# DOS, etc.

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

# Mac

print "Hello world\n"

(then Run "Myscript" or Shift-Command-R)

# 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 interpreter. Under Unix, the first two often work. Under

DOS, it's entirely possible that neither works. If 4DOS was the com-

mand shell, you'd probably have better luck like this:

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

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.] WWhheerree ccaann II lleeaarrnn aabboouutt CCGGII oorr WWeebb pprrooggrraammmmiinngg iinn PPeerrll?? For modules, get the CGI or LWP modules from CPAN. For textbooks, see the two especially dedicated to web stuff in the question on books. For problems and questions related to the web, like ``Why do I get 500 Errors'' or ``Why doesn't it run from the browser right when it runs

fine on the command line'', see the troubleshooting guides and refer-

ences in perlfaq9 or in the CGI MetaFAQ: http://www.perl.org/CGIMetaFAQ.html

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

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.perl-

doc.com/ , but consider upgrading your perl.)

A good book on OO on Perl is the "Object-Oriented Perl" by Damian Con-

way from Manning Publications, http://www.manning.com/Conway/index.html WWhheerree ccaann II lleeaarrnn aabboouutt lliinnkkiinngg CC wwiitthh PPeerrll?? [[hh22xxss,, xxssuubbpppp]] 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 mod-

ules wrote their code and solved their problems. II''vvee rreeaadd ppeerrlleemmbbeedd,, ppeerrllgguuttss,, eettcc..,, bbuutt II ccaann''tt eemmbbeedd ppeerrll iinn mmyy CC pprrooggrraamm;; wwhhaatt aamm II ddooiinngg wwrroonngg?? Download the ExtUtils::Embed kit from CPAN and run `make test'. If the tests pass, read the pods again and again and again. If they fail, see

perlbug and send a bug report with the output of "make test TESTVER-

BOSE=1" along with "perl -V".

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

use diagnostics -verbose;

WWhhaatt''ss MMaakkeeMMaakkeerr?? This module (part of the standard Perl distribution) is designed to write a Makefile for an extension module from a Makefile.PL. For more information, see ExtUtils::MakeMaker. AUTHOR AND COPYRIGHT

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 v5.8.6 2004-11-05 PERLFAQ3(1)