PERLFAQ3(1) Perl Programmers Reference Guide PERLFAQ3(1)NAMEperlfaq3 - Programming Tools ($Revision: 1.38 $, $Date:
1999/05/23 16:08:30 $)
DESCRIPTION
This section of the FAQ answers questions related to pro
grammer tools and programming support.
How do I do (anything)?
Have you looked at CPAN (see the perlfaq2 manpage)? 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 the perltoc manpage.
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 imme
diately evaluated. You can also examine the symbol table,
get stack backtraces, check variable values, set break
points, 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 impor
tantly) 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 the perltrap manpage? 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 the perlde
bug manpage? 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 Bench
mark.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 the
perlstyle manpage, 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 sig
nificant 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 char
acters 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 exam
ple, 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/work
ing.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/Prod
ucts/Komodo/index.html). (Visual Perl, a Visual Stu
dio.NET plug-in is currently (early 2001) in beta
(http://www.ActiveState.com/Products/Visu
alPerl/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 inte
grated development environment for Windows that sup
ports Perl development.
Perl code magic
(http://www.petes-place.com/codemagic.html).
visiPerl+
http://helpconsulting.net/visiperl/, from Help Con
sulting.
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.source
forge.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.red
hat.com/cygwin/)
Ksh from the MKS Toolkit (http://www.mks.com/), or the
Bourne shell of the U/WIN environment
(http://www.research.att.com/sw/tools/uwin/)
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 educa
tional 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 con
trast 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 sensitiv
ity 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 edi
tors 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 configura
tion file, see http://www.perl.com/CPAN/authors/Tom_Chris
tiansen/scripts/toms.exrc.gz , the standard benchmark file
for vi emulators. The file runs best with nvi, the cur
rent 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 load
able object module interface to a curses library. A small
demo can be found at the directory
http://www.perl.com/CPAN/authors/Tom_Chris
tiansen/scripts/rep; this program repeats a command and
updates the screen as needed, rendering rep ps axu similar
to top.
How can I use X or Tk with Perl?
Tk is a completely Perl-based, object-oriented interface
to the Tk toolkit that doesn't force you to use Tcl just
to get at Tk. Sx is an interface to the Athena Widget
set. Both are available from CPAN. See the directory
http://www.perl.com/CPAN/modules/by-cate
gory/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 .
How can I generate simple menus without using CGI or Tk?
The http://www.perl.com/CPAN/authors/id/SKUNZ/perl
menu.v4.0.tar.gz module, which is curses-based, can help
with this.
What is undump?
See the next question on ``How can I make my Perl program
run faster?''
How can I make my Perl program run faster?
The best way to do this is to come up with a better algo
rithm. This can often make a dramatic difference. Jon
Bentley's book ``Programming Pearls'' (that's not a mis
spelling!) has some good tips on optimization, too.
Advice on benchmarking boils down to: benchmark and pro
file 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 hard
ware.
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 com
piler 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 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 vec
tor--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 mod
ules.
Another thing to try is learning whether your Perl was
compiled with the system malloc or with Perl's builtin
malloc. Whichever one it is, try using the other one and
see whether this makes a difference. Information about
malloc is in the INSTALL file in the source distribution.
You can find out whether you are using perl's malloc by
typing "perl -V:usemymalloc".
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";
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,
"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.
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 (avail
able 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 exe
cutes it within the same address space without forking.
The Apache extension also gives Perl access to the inter
nal 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 mod
ule (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-cate
gory/15_World_Wide_Web_HTML_HTTP_CGI/ .
A non-free, commercial product, ``The Velocity Engine for
Perl'', (http://www.binevolve.com/ or
http://www.binevolve.com/velocigen/ ) might also be worth
looking at. It will allow you to increase the performance
of your Perl programs, running programs up to 25 times
faster than normal CGI Perl when running in persistent
Perl mode or 4 to 5 times faster without any modification
to your existing CGI programs. Fully functional evaluation
copies are available from the web site.
How can I hide the source for my Perl program?
Delete it. :-) Seriously, there are a number of (mostly
unsatisfactory) solutions with varying levels of ``secu
rity''.
First of all, however, you can't take away read permis
sion, 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 (Filter::*
from CPAN), but any decent programmer will be able to
decrypt it. You can try using the byte code compiler and
interpreter described below, but the curious might still
be able to de-compile it. You can try using the native-
code compiler described below, but crackers might be able
to disassemble it. These pose varying degrees of diffi
culty to people wanting to get at your code, but none can
definitively conceal it (true of every language, not just
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 soft
ware 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 com
piler, available from CPAN, that can do both these things.
It is included in the perl5.005 release, but is still con
sidered 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 guaran
tee 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 sig
nificantly (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 cur
rently 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.
How can I compile Perl into Java?
You can also integrate Java and Perl with the Perl
Resource Kit from O'Reilly and Associates. See
http://www.oreilly.com/catalog/prkunix/ .
Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still
in development, allows Perl code to be called from Java.
See jpl/README in the Perl source tree.
How can I get "#!perl" to work on [MS-DOS,NT,...]?
For OS/2 just use
extproc perl -S -your_switches
as the first line in "*.cmd" file ("-S" due to a bug in
cmd.exe's `extproc' handling). For DOS one should first
invent a corresponding batch file and codify it in "ALTER
NATIVE_SHEBANG" (see the INSTALL file in the source dis
tribution for more information).
The Win95/NT installation, when using the ActiveState port
of Perl, will modify the Registry to associate the ".pl"
extension with the perl interpreter. If you install
another port, perhaps even building your own Win95/NT Perl
from the standard sources by using a Windows port of gcc
(e.g., with cygwin or mingw32), then you'll have to modify
the Registry yourself. In addition to associating ".pl"
with the interpreter, NT people can use: "SET
PATHEXT=%PATHEXT%;.PL" to let them run the program
"install-linux.pl" merely by typing "install-linux".
Macintosh Perl programs will have the appropriate Creator
and Type, so that double-clicking them will invoke the
Perl application.
IMPORTANT!: Whatever you do, PLEASE don't get frustrated,
and just throw the perl interpreter into your cgi-bin
directory, in order to get your programs working for a web
server. This is an EXTREMELY big security risk. Take the
time to figure out how to do it correctly.
Can I write useful Perl programs on the command line?
Yes. Read the perlrun manpage for more information. Some
examples follow. (These assume standard Unix shell quot
ing 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. :-)
Why don't Perl one-liners work on my DOS/Mac/VMS system?
The problem is usually that the command interpreters on
those systems have rather different ideas about quoting
than the Unix shells under which the one-liners were cre
ated. 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)
# 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 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 eas
ier to write.
There is no general solution to all of this. It is a
mess, pure and simple. Sucks to be away from Unix, huh?
:-)
[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 these sources:
WWW Security FAQ
http://www.w3.org/Security/Faq/
Web FAQ
http://www.boutell.com/faq/
CGI FAQ
http://www.webthing.com/tutorials/cgifaq.html
HTTP Spec
http://www.w3.org/pub/WWW/Protocols/HTTP/
HTML Spec
http://www.w3.org/TR/REC-html40/
http://www.w3.org/pub/WWW/MarkUp/
CGI Spec
http://www.w3.org/CGI/
CGI Security FAQ
http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
Where can I learn about object-oriented Perl programming?
A good place to start is the perltoot manpage, and you can
use the perlobj manpage, the perlboot manpage, and the
perlbot manpage for reference. Perltoot didn't come out
until the 5.004 release; you can get a copy (in pod, html,
or postscript) from
http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
Where can I learn about linking C with Perl? [h2xs,
xsubpp]
If you want to call C from Perl, start with the perlxstut
manpage, moving on to the perlxs manpage, the xsubpp man
page, and the perlguts manpage. If you want to call Perl
from C, then read the perlembed manpage, the perlcall man
page, and the perlguts manpage. Don't forget that you can
learn a lot from looking at how the authors of existing
extension modules wrote their code and solved their prob
lems.
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 the perlbug manpage 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 the perldiag manpage. 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;
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 the ExtU
tils::MakeMaker manpage.
AUTHOR AND COPYRIGHT
Copyright (c) 1997-1999 Tom Christiansen and Nathan Tork
ington. All rights reserved.
When included as an integrated part of the Standard Dis
tribution of Perl or of its documentation (printed or oth
erwise), this works is covered under Perl's Artistic
License. For separate distributions of all or part of
this FAQ outside of that, see the perlfaq manpage.
Irrespective of its distribution, all code examples here
are in the public domain. You are permitted and encour
aged to use this code and any derivatives thereof in your
own programs for fun or for profit as you see fit. A sim
ple comment in the code giving credit to the FAQ would be
courteous but is not required.
2001-04-07 perl v5.6.1 PERLFAQ3(1)
