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perlfaq3 - Programming Tools
This section of the FAQ answers questions related to programmer tools and programming
support.
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)
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A crude table of contents for the Perl manpage set is found in perltoc.
The typical approach uses the Perl debugger, described in the perldebug(1) manpage, on an
``empty'' program, like this:
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.
In general, not yet. There is psh available at
http://www.focusresearch.com/gregor/psh
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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.
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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.
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";
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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.
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 },
});
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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)
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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.
The B::Xref module can be used to generate cross-reference reports for Perl programs.
perl -MO=Xref[,OPTIONS] scriptname.plx
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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
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 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
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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 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps does lots of things related
to generating nicely printed output of documents, as does enscript at http://people.ssh.fi/mtr/genscript/
.
Recent versions of ctags do much more than older versions did. EXUBERANT 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.
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 an IDE, check the following:
- Komodo
- 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 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,
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
distribution under Windows 95/98/NT/2000.
- PerlBuilder
- ( http://www.solutionsoft.com/perl.htm ) is an integrated development environment for
Windows that supports Perl development.
- visiPerl+
- ( http://helpconsulting.net/visiperl/ ) From Help Consulting, for Windows.
- OptiPerl
- ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI environment, including
debugger and syntax highlighting editor.
For Windows there's also the
- CodeMagicCD
- ( http://www.codemagiccd.com/ ) Collection of various programming tools for Windows: Perl
(5.005_03), TclTk, Python, GNU programming tools, REBOL, wxWindows toolkit, the MinGW GNU
C/C++ compiler, DJGPP GNU C/C++ compiler, Cint C interpreter, YaBasic.
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 Mac OS, 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/ ). Mac OS X users can use Unix editors as well.
- 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
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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/ ).
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/ .
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.
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
; this program repeats a command and updates the screen as needed, rendering rep ps axu
similar to top.
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/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.cpan.org/authors/Stephen_O_Lidie/ , and
the online manpages at http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz module, which is curses-based,
can help with this.
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).
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 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.
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 INSTALL file in the source
distribution. 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 (<FILE>) {
# ...
}
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instead of this:
#
# Bad Idea
#
@data = <FILE>;
foreach (@data) {
# ...
}
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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/} <FILE>;
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will cause the entire file to be slurped. For large files, it's better to loop:
while (<FILE>) {
push(@wanted, $_) if /pattern/;
}
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- * Avoid unnecessary quotes and
stringification
-
Don't quote large strings unless absolutely necessary:
my $copy = "$large_string";
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makes 2 copies of $large_string (one for $copy and another for the quotes), whereas
my $copy = $large_string;
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only makes one copy.
Ditto for stringifying large arrays:
{
local $, = "\n";
print @big_array;
}
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is much more memory-efficient than either
print join "\n", @big_array;
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or
{
local $" = "\n";
print "@big_array";
}
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- * 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 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.
- * 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.
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";
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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.
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 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-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.
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 crackers might be able to disassemble 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).
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.
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.
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.
For OS/2 just use
extproc perl -S -your_switches
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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 ALTERNATIVE_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 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.
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"}'
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OK, the last one was actually an Obfuscated Perl Contest entry. :-)
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"""
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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>""
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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.]
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:
http://www.perl.org/CGI_MetaFAQ.html
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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 Publications, http://www.manning.com/Conway/index.html
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 modules wrote their code
and solved their problems.
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.
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
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or change your program to explain the messages for you:
or
use diagnostics -verbose;
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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 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.
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