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.
You can also use Devel::REPL which is an interactive shell for Perl, commonly known as a REPL - Read, Evaluate, Print, Loop. It provides various handy features.
$ cpan -l
You can also use "cpan"'s "-a" switch to create an autobundle file that "CPAN.pm" understands and can use to re-install every module:
$ cpan -a
Inside a Perl program, you can use the ExtUtils::Installed module to show all installed distributions, 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->
extras({follow => 1})->
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(
{
wanted => sub {
push @files, $File::Find::fullname
if -f $File::Find::fullname && /\.pm$/
},
follow => 1,
follow_skip => 2,
},
@INC
);
print join "\n", @files;
If you simply need to check quickly 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):
$ 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
(If you don't receive a ``Can't locate ... in @INC'' error message, then Perl found the module name you asked for.)
Before you do anything else, you can help yourself by ensuring that you let Perl tell you about problem areas in your code. By turning on warnings and strictures, you can head off many problems before they get too big. You can find out more about these in strict and warnings.
#!/usr/bin/perl
use strict;
use warnings;
Beyond that, the simplest debugger is the "print" function. Use it to look at values as you run your program:
print STDERR "The value is [$value]\n";
The Data::Dumper module can pretty-print Perl data structures:
use Data::Dumper qw( Dumper );
print STDERR "The hash is " . Dumper( \%hash ) . "\n";
Perl comes with an interactive debugger, which you can start with the "-d" switch. It's fully explained in perldebug.
If you'd like a graphical user interface and you have Tk, you can use "ptkdb". It's on CPAN and available for free.
If you need something much more sophisticated and controllable, Leon Brocard's Devel::ebug (which you can call with the "-D" switch as "-Debug") gives you the programmatic hooks into everything you need to write your own (without too much pain and suffering).
You can also use a commercial debugger such as Affrus (Mac OS X), Komodo from Activestate (Windows and Mac OS X), or EPIC (most platforms).
The "Devel" namespace has several modules which you can use to profile your Perl programs.
The Devel::NYTProf (New York Times Profiler) does both statement and subroutine profiling. It's available from CPAN and you also invoke it with the "-d" switch:
perl -d:NYTProf some_perl.pl
It creates a database of the profile information that you can turn into reports. The "nytprofhtml" command turns the data into an HTML report similar to the Devel::Cover report:
nytprofhtml
You might also be interested in using the Benchmark to measure and compare code snippets.
You can read more about profiling in Programming Perl, chapter 20, or Mastering Perl, chapter 5.
perldebguts documents creating a custom debugger if you need to create a special sort of profiler. brian d foy describes the process in The Perl Journal, ``Creating a Perl Debugger'', <http://www.ddj.com/184404522> , and ``Profiling in Perl'' <http://www.ddj.com/184404580> .
Perl.com has two interesting articles on profiling: ``Profiling Perl'', by Simon Cozens, <http://www.perl.com/lpt/a/850> and ``Debugging and Profiling mod_perl Applications'', by Frank Wiles, <http://www.perl.com/pub/a/2006/02/09/debug_mod_perl.html> .
Randal L. Schwartz writes about profiling in ``Speeding up Your Perl Programs'' for Unix Review, <http://www.stonehenge.com/merlyn/UnixReview/col49.html> , and ``Profiling in Template Toolkit via Overriding'' for Linux Magazine, <http://www.stonehenge.com/merlyn/LinuxMag/col75.html> .
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>
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.
Camelcade plugin provides Perl5 support in IntelliJ IDEA and other JetBrains IDEs.
GUI editor written in Perl using wxWidgets and Scintilla with lots of smaller features. Aims for a UI based on Perl principles like TIMTOWTDI and ``easy things should be easy, hard things should be possible''.
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.
Padre is cross-platform IDE for Perl written in Perl using wxWidgets to provide a native look and feel. It's open source under the Artistic License. It is one of the newer Perl IDEs.
PerlBuilder 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 Windows 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.barebones.com/products/bbedit/> ) or Alpha ( <http://www.his.com/~jguyer/Alpha/Alpha8.html> ). MacOS X users can use Unix editors as well.
or a vi clone such as
The following are Win32 multilanguage editor/IDEs 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://ptkdb.sourceforge.net/> ) 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
Cygwin is covered by the GNU General Public License (but that shouldn't matter for Perl use). Cygwin contains (in addition to the shell) a comprehensive set of standard Unix toolkit utilities.
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.
For CPerlMode, see <http://www.emacswiki.org/cgi-bin/wiki/CPerlMode>
There are a number of modules which let you write GUIs in Perl. Most GUI toolkits have a perl interface: an incomplete list follows.
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 (my $line = <$file_handle>) {
# ...
}
instead of this:
#
# Bad Idea
#
my @data = <$file_handle>;
foreach (@data) {
# ...
}
When the files you're processing are small, it doesn't much matter which way you do it, but it makes a huge difference when they start getting larger.
@wanted = grep {/pattern/} <$file_handle>;
will cause the entire file to be slurped. For large files, it's better to loop:
while (<$file_handle>) {
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() 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 three 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.
Finally, Plack is a Perl module and toolkit that contains PSGI middleware, helpers and adapters to web servers, allowing you to easily deploy scripts which can continue running, and provides flexibility with regards to which web server you use. It can allow existing CGI scripts to enjoy this flexibility and performance with minimal changes, or can be used along with modern Perl web frameworks to make writing and deploying web services with Perl a breeze.
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 also <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 later in perlfaq3, but the curious might still be able to de-compile it. You can try using the native-code compiler described later, 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/> ) is Perl's analog to Java's JAR. It's freely available and on CPAN ( <http://search.cpan.org/dist/PAR/> ).
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.
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 (including Mac OS X)
perl -e 'print "Hello world\n"'
# DOS, etc.
perl -e "print \"Hello world\n\""
# Mac Classic
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.]
L<http://www.perl.org/CGI_MetaFAQ.html>
Looking in to Plack and modern Perl web frameworks is highly recommended, though; web programming in Perl has evolved a long way from the old days of simple CGI scripts.
A good book on OO on Perl is the ``Object-Oriented Perl'' by Damian Conway from Manning Publications, or ``Intermediate Perl'' by Randal Schwartz, brian d foy, 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;
The ExtUtils::MakeMaker module, better known simply as ``MakeMaker'', turns a Perl script, typically called "Makefile.PL", into a Makefile. The Unix tool "make" uses this file to manage dependencies and actions to process and install a Perl distribution.
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.