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perlfaq3 - Programming Tools ($Revision: 1.56 $, $Date: 2005/12/31 00:54:37 $)
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.
perl -de 42
Now just type in any legal Perl code, and it will be immediately evaluated. You can also examine the symbol table, get stack backtraces, check variable values, set breakpoints, and other operations typically found in symbolic debuggers.
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://zoidberg.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.
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 $File::Find::name && /\.pm$/
},
@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 documentation, 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
Have you tried "use strict"? It prevents you from using symbolic references, makes you predeclare any subroutines that you call as bare words, and (probably most importantly) forces you to predeclare your variables with "my", "our", or "use vars".
Did you check the return values of each and every system call? The operating system (and thus Perl) tells you whether they worked, and if not why.
open(FH, "> /etc/cantwrite")
or die "Couldn't write to /etc/cantwrite: $!\n";
Did you read perltrap? It's full of gotchas for old and new Perl programmers and even has sections for those of you who are upgrading from languages like awk and C.
Have you tried the Perl debugger, described in perldebug? You can step through your program and see what it's doing and thus work out why what it's doing isn't what it should be doing.
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;
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.
perl -MO=Xref[,OPTIONS] scriptname.plx
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
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.gz does lots of things related to generating nicely printed output of documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
Exuberent ctags supports Perl: http://ctags.sourceforge.net/
You might also try pltags: http://www.mscha.com/pltags.zip
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 (in alphabetical order, not order of preference):
The Eclipse Perl Integration Project integrates Perl editing/debugging with Eclipse.
Perl Editor by EngInSite is a complete integrated development environment (IDE) for creating, testing, and debugging Perl scripts; the tool runs on Windows 9x/NT/2000/XP or later.
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.
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.
OptiPerl is a Windows IDE with simulated CGI environment, including debugger and syntax highlighting editor.
PerlBuidler is an integrated development environment for Windows that supports Perl development.
From Help Consulting, for Windows.
Visual Perl is a Visual Studio.NET plug-in from ActiveState.
Zeus for Window is another Win32 multi-language editor/IDE that comes with support for Perl:
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 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. Neil Bowers (the man behind Geekcruises) has a list of Mac editors that can handle Perl ( http://www.neilbowers.org/macperleditors.html ).
or a vi clone such as
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:
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 creation.
In addition to an editor/IDE you might be interested in a more powerful shell environment for Win32. Your options include
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).
Pepper and Pe are programming language sensitive text editors for Mac OS X and BeOS respectively ( http://www.hekkelman.com/ ).
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.
Invaluable for Perl/Tk programming are the Perl/Tk FAQ at http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.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 .
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 executable, 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.
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:
#
# Good Idea
#
while (<FILE>) {
# ...
}
instead of this:
#
# Bad Idea
#
@data = <FILE>;
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.
@wanted = grep {/pattern/} <FILE>;
will cause the entire file to be slurped. For large files, it's better to loop:
while (<FILE>) {
push(@wanted, $_) if /pattern/;
}
my $copy = "$large_string";
makes 2 copies of $large_string (one for $copy and another for the quotes), whereas
my $copy = $large_string;
only makes one copy.
Ditto for stringifying large arrays:
{
local $, = "\n";
print @big_array;
}
is much more memory-efficient than either
print join "\n", @big_array;
or
{
local $" = "\n";
print "@big_array";
}
sub makeone {
my @a = ( 1 .. 10 );
return \@a;
}
for ( 1 .. 10 ) {
push @many, makeone();
}
print $many[4][5], "\n";
print "@many\n";
You usually can't. Memory allocated to lexicals (i.e. my() variables) cannot be reclaimed or reused even if they go out of scope. It is reserved in case the variables come back into scope. Memory allocated to global variables can be reused (within your program) by using undef()ing and/or delete().
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.
In general, memory allocation and de-allocation isn't something you can or should be worrying about much in Perl.
See also ``How can I make my Perl program take less memory?''
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/ .
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).
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.
In general, you can't do this. There are some things that may work for your situation though. People usually ask this question because they want to distribute their works without giving away the source code, and most solutions trade disk space for convenience. You probably won't see much of a speed increase either, since most solutions simply bundle a Perl interpreter in the final product (but see ``How can I make my Perl program run faster?'').
The Perl Archive Toolkit ( http://par.perl.org/index.cgi ) is Perl's analog to Java's JAR. It's freely available and on CPAN ( http://search.cpan.org/dist/PAR/ ).
The B::* namespace, often called ``the Perl compiler'', but is really a way for Perl programs to peek at its innards rather than create pre-compiled versions of your program. However. the B::Bytecode module can turn your script into a bytecode format that could be loaded later by the ByteLoader module and executed as a regular Perl script.
There are also some commercial products that may work for you, although you have to buy a license for them.
The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ ) from ActiveState can ``Turn your Perl programs into ready-to-run executables for HP-UX, Linux, Solaris and Windows.''
Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line program for converting perl scripts to executable files. It targets both Windows and unix platforms.
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.
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 "ALTERNATE_SHEBANG" (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 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".
Under ``Classic'' MacOS, a perl program will have the appropriate Creator and Type, so that double-clicking them will invoke the MacPerl application. Under Mac OS X, clickable apps can be made from any "#!" script using Wil Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
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.
# 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. :-)
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 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 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.]
http://www.perl.org/CGI_MetaFAQ.html
A good book on OO on Perl is the ``Object-Oriented Perl'' by Damian Conway from Manning Publications, or ``Learning Perl References, Objects, & Modules'' by Randal Schwartz and Tom Phoenix from O'Reilly Media.
You might not need all the power of XS. The Inline::C module lets you put C code directly in your Perl source. It handles all the magic to make it work. You still have to learn at least some of the perl API but you won't have to deal with the complexity of the XS support files.
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;
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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