PERLFAQ3(1) Perl Programmers Reference Guide PERLFAQ3(1) #
PERLFAQ3(1) Perl Programmers Reference Guide PERLFAQ3(1)
NNAAMMEE #
perlfaq3 - Programming Tools
VVEERRSSIIOONN #
version 5.20210520
DDEESSCCRRIIPPTTIIOONN #
This section of the FAQ answers questions related to programmer tools and
programming support.
HHooww ddoo II ddoo ((aannyytthhiinngg))?? Have you looked at CPAN (see perlfaq2)? The chances are that someone has already written a module that can solve your problem. Have you read the appropriate manpages? Here’s a brief index:
Basics
perldata - Perl data types
perlvar - Perl pre-defined variables
perlsyn - Perl syntax
perlop - Perl operators and precedence
perlsub - Perl subroutines
Execution
perlrun - how to execute the Perl interpreter
perldebug - Perl debugging
Functions
perlfunc - Perl builtin functions
Objects
perlref - Perl references and nested data structures
perlmod - Perl modules (packages and symbol tables)
perlobj - Perl objects
perltie - how to hide an object class in a simple variable
Data Structures
perlref - Perl references and nested data structures
perllol - Manipulating arrays of arrays in Perl
perldsc - Perl Data Structures Cookbook
Modules
perlmod - Perl modules (packages and symbol tables)
perlmodlib - constructing new Perl modules and finding existing ones
Regexes
perlre - Perl regular expressions
perlfunc - Perl builtin functions>
perlop - Perl operators and precedence
perllocale - Perl locale handling (internationalization and
localization)
Moving to perl5
perltrap - Perl traps for the unwary
perl
Linking with C
perlxstut - Tutorial for writing XSUBs
perlxs - XS language reference manual
perlcall - Perl calling conventions from C
perlguts - Introduction to the Perl API
perlembed - how to embed perl in your C program
Various
<http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz> (not a man-page but
still useful, a collection of various essays on Perl techniques)
A crude table of contents for the Perl manpage set is found in perltoc.
HHooww ccaann II uussee PPeerrll iinntteerraaccttiivveellyy?? The typical approach uses the Perl debugger, described in the ppeerrllddeebbuugg(1) manpage, on an “empty” program, like this:
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.
HHooww ddoo II ffiinndd wwhhiicchh mmoodduulleess aarree iinnssttaalllleedd oonn mmyy ssyysstteemm?? From the command line, you can use the “cpan” command’s “-l” switch:
$ 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.)
HHooww ddoo II ddeebbuugg mmyy PPeerrll pprrooggrraammss?? (contributed by brian d foy)
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).
HHooww ddoo II pprrooffiillee mmyy PPeerrll pprrooggrraammss?? (contributed by brian d foy, updated Fri Jul 25 12:22:26 PDT 2008)
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 _P_r_o_g_r_a_m_m_i_n_g _P_e_r_l, chapter 20, or
_M_a_s_t_e_r_i_n_g _P_e_r_l, 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 _T_h_e _P_e_r_l
_J_o_u_r_n_a_l, "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, <https://www.perl.com/pub/2004/06/25/profiling.html/> 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 _U_n_i_x _R_e_v_i_e_w,
<http://www.stonehenge.com/merlyn/UnixReview/col49.html> , and "Profiling
in Template Toolkit via Overriding" for _L_i_n_u_x _M_a_g_a_z_i_n_e,
<http://www.stonehenge.com/merlyn/LinuxMag/col75.html> .
HHooww ddoo II ccrroossss--rreeffeerreennccee mmyy PPeerrll pprrooggrraammss?? The B::Xref module can be used to generate cross-reference reports for Perl programs.
perl -MO=Xref[,OPTIONS] scriptname.plx
IIss tthheerree aa pprreettttyy--pprriinntteerr ((ffoorrmmaatttteerr)) ffoorr PPeerrll?? Perl::Tidy comes with a perl script perltidy 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, or spend much time reading Perl, you will probably find it useful.
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 _._e_x_r_c 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/T/TO/TOMC/scripts/toms.exrc.gz>
IIss tthheerree aann IIDDEE oorr WWiinnddoowwss PPeerrll EEddiittoorr?? Perl programs are just plain text, so any editor will do.
If you're on Unix, you already have an IDE--Unix itself. The Unix
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):
Eclipse
<http://e-p-i-c.sf.net/>
The Eclipse Perl Integration Project integrates Perl
editing/debugging with Eclipse.
Enginsite
<http://www.enginsite.com/>
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.
IntelliJ IDEA
<https://plugins.jetbrains.com/plugin/7796>
Camelcade plugin provides Perl5 support in IntelliJ IDEA and other
JetBrains IDEs.
Kephra
<http://kephra.sf.net>
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".
Komodo
<http://www.ActiveState.com/Products/Komodo/>
ActiveState's cross-platform (as of October 2004, that's Windows,
Linux, and Solaris), multi-language IDE has Perl support, including a
regular expression debugger and remote debugging.
Notepad++
<http://notepad-plus.sourceforge.net/>
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.
OptiPerl
<http://www.optiperl.com/>
OptiPerl is a Windows IDE with simulated CGI environment, including
debugger and syntax-highlighting editor.
Padre
<http://padre.perlide.org/>
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
<http://www.solutionsoft.com/perl.htm>
PerlBuilder is an integrated development environment for Windows that
supports Perl development.
visiPerl+
<http://helpconsulting.net/visiperl/index.html>
From Help Consulting, for Windows.
Visual Perl
<http://www.activestate.com/Products/Visual_Perl/>
Visual Perl is a Visual Studio.NET plug-in from ActiveState.
Zeus
<http://www.zeusedit.com/lookmain.html>
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.
GNU Emacs
<http://www.gnu.org/software/emacs/windows/ntemacs.html>
MicroEMACS
<http://www.microemacs.de/>
XEmacs
<http://www.xemacs.org/Download/index.html>
Jed <http://space.mit.edu/~davis/jed/>
or a vi clone such as
Vim <http://www.vim.org/>
Vile
<http://invisible-island.net/vile/vile.html>
The following are Win32 multilanguage editor/IDEs that support Perl:
MultiEdit
<http://www.MultiEdit.com/>
SlickEdit
<http://www.slickedit.com/>
ConTEXT
<http://www.contexteditor.org/>
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
bash
from the Cygwin package ( <http://cygwin.com/> )
zsh <http://www.zsh.org/>
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.
BBEdit and TextWrangler
are text editors for OS X that have a Perl sensitivity mode (
<http://www.barebones.com/> ).
WWhheerree ccaann II ggeett PPeerrll mmaaccrrooss ffoorr vvii?? For a complete version of Tom Christiansen’s vi configuration file, see http://www.cpan.org/authors/id/T/TO/TOMC/scripts/toms.exrc.gz , the standard benchmark file for vi emulators. The file runs best with nvi, the current version of vi out of Berkeley, which incidentally can be built with an embedded Perl interpreter–see http://www.cpan.org/src/misc/ .
WWhheerree ccaann II ggeett ppeerrll--mmooddee oorr ccppeerrll--mmooddee ffoorr eemmaaccss?? Since Emacs version 19 patchlevel 22 or so, there have been both a perl-mode.el and support for the Perl debugger built in. These should come with the standard Emacs 19 distribution.
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>
HHooww ccaann II uussee ccuurrsseess wwiitthh PPeerrll?? 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/id/T/TO/TOMC/scripts/rep.gz ; this program repeats a command and updates the screen as needed, rendering rreepp ppss aaxxuu similar to ttoopp.
HHooww ccaann II wwrriittee aa GGUUII ((XX,, TTkk,, GGttkk,, eettcc..)) iinn PPeerrll?? (contributed by Ben Morrow)
There are a number of modules which let you write GUIs in Perl. Most GUI
toolkits have a perl interface: an incomplete list follows.
Tk This works under Unix and Windows, and the current version doesn't
look half as bad under Windows as it used to. Some of the gui
elements still don't 'feel' quite right, though. The interface is
very natural and 'perlish', making it easy to use in small scripts
that just need a simple gui. It hasn't been updated in a while.
Wx This is a Perl binding for the cross-platform wxWidgets toolkit (
<http://www.wxwidgets.org> ). It works under Unix, Win32 and Mac OS
X, using native widgets (Gtk under Unix). The interface follows the
C++ interface closely, but the documentation is a little sparse for
someone who doesn't know the library, mostly just referring you to
the C++ documentation.
Gtk and Gtk2
These are Perl bindings for the Gtk toolkit ( <http://www.gtk.org> ).
The interface changed significantly between versions 1 and 2 so they
have separate Perl modules. It runs under Unix, Win32 and Mac OS X
(currently it requires an X server on Mac OS, but a 'native' port is
underway), and the widgets look the same on every platform: i.e.,
they don't match the native widgets. As with Wx, the Perl bindings
follow the C API closely, and the documentation requires you to read
the C documentation to understand it.
Win32::GUI
This provides access to most of the Win32 GUI widgets from Perl.
Obviously, it only runs under Win32, and uses native widgets. The
Perl interface doesn't really follow the C interface: it's been made
more Perlish, and the documentation is pretty good. More advanced
stuff may require familiarity with the C Win32 APIs, or reference to
MSDN. #
CamelBones
CamelBones ( <http://camelbones.sourceforge.net> ) is a Perl
interface to Mac OS X's Cocoa GUI toolkit, and as such can be used to
produce native GUIs on Mac OS X. It's not on CPAN, as it requires
frameworks that CPAN.pm doesn't know how to install, but installation
is via the standard OSX package installer. The Perl API is, again,
very close to the ObjC API it's wrapping, and the documentation just
tells you how to translate from one to the other.
Qt There is a Perl interface to TrollTech's Qt toolkit, but it does not
appear to be maintained.
Athena
Sx is an interface to the Athena widget set which comes with X, but
again it appears not to be much used nowadays.
HHooww ccaann II mmaakkee mmyy PPeerrll pprrooggrraamm rruunn ffaasstteerr?? The best way to do this is to come up with a better algorithm. This can often make a dramatic difference. Jon Bentley’s book _P_r_o_g_r_a_m_m_i_n_g _P_e_a_r_l_s (that’s not a misspelling!) has some good tips on optimization, too. Advice on benchmarking boils down to: benchmark and profile to make sure you’re optimizing the right part, look for better algorithms instead of microtuning your code, and when all else fails consider just buying faster hardware. You will probably want to read the answer to the earlier question “How do I profile my Perl programs?” if you haven’t done so already.
A different approach is to autoload seldom-used Perl code. See the
AutoSplit and AutoLoader modules in the standard distribution for that.
Or you could locate the bottleneck and think about writing just that part
in C, the way we used to take bottlenecks in C code and write them in
assembler. Similar to rewriting in C, modules that have critical sections
can be written in C (for instance, the PDL module from CPAN).
If you're currently linking your perl executable to a shared _l_i_b_c_._s_o, 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
_I_N_S_T_A_L_L file in the source distribution for more information.
The undump program was an ancient attempt to speed up Perl program by
storing the already-compiled form to disk. This is no longer a viable
option, as it only worked on a few architectures, and wasn't a good
solution anyway.
HHooww ccaann II mmaakkee mmyy PPeerrll pprrooggrraamm ttaakkee lleessss mmeemmoorryy?? When it comes to time-space tradeoffs, Perl nearly always prefers to throw memory at a problem. Scalars in Perl use more memory than strings in C, arrays take more than that, and hashes use even more. While there’s still a lot to be done, recent releases have been addressing these issues. For example, as of 5.004, duplicate hash keys are shared amongst all hashes using them, so require no reallocation.
In some cases, using ssuubbssttrr(()) or vveecc(()) 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 _I_N_S_T_A_L_L 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 (my $line = <$file_handle>) {
# ...
}
instead of this:
#
# Bad Idea
#
my @data = <$file_handle>;
foreach (@data) {
# ...
}
When the files you're processing are small, it doesn't much matter
which way you do it, but it makes a huge difference when they start
getting larger.
Use map and grep selectively
Remember that both map and grep expect a LIST argument, so doing
this:
@wanted = grep {/pattern/} <$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/;
}
Avoid unnecessary quotes and stringification
Don't quote large strings unless absolutely necessary:
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";
}
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 judgement, 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.
IIss iitt ssaaffee ttoo rreettuurrnn aa rreeffeerreennccee ttoo llooccaall oorr lleexxiiccaall ddaattaa?? Yes. Perl’s garbage collection system takes care of this so everything works out right.
sub makeone {
my @a = ( 1 .. 10 );
return \@a;
}
for ( 1 .. 10 ) {
push @many, makeone();
}
print $many[4][5], "\n";
print "@many\n";
HHooww ccaann II ffrreeee aann aarrrraayy oorr hhaasshh ssoo mmyy pprrooggrraamm sshhrriinnkkss?? (contributed by Michael Carman)
You usually can't. Memory allocated to lexicals (i.e. mmyy(()) 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 uunnddeeff(())
and/or ddeelleettee(()).
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
mmmmaapp(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?"
HHooww ccaann II mmaakkee mmyy CCGGII ssccrriipptt mmoorree eeffffiicciieenntt?? Beyond the normal measures described to make general Perl programs faster or smaller, a CGI program has additional issues. It may be run several times per second. Given that each time it runs it will need to be re- compiled and will often allocate a megabyte or more of system memory, this can be a killer. Compiling into C iissnn’’tt ggooiinngg ttoo hheellpp yyoouu because the process start-up overhead is where the bottleneck is.
There are 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/>
.
HHooww ccaann II hhiiddee tthhee ssoouurrccee ffoorr mmyy PPeerrll pprrooggrraamm?? Delete it. :-) Seriously, there are a number of (mostly unsatisfactory) solutions with varying levels of “security”.
First of all, however, you _c_a_n_'_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.
HHooww ccaann II ccoommppiillee mmyy PPeerrll pprrooggrraamm iinnttoo bbyyttee ccooddee oorr CC?? (contributed by brian d foy)
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 is Perl's analog to Java's JAR. It's freely
available and on CPAN ( <https://metacpan.org/pod/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.
HHooww ccaann II ggeett “”##!!ppeerrll"" ttoo wwoorrkk oonn [[MMSS--DDOOSS,,NNTT,,......]]?? 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 "ALTERNATE_SHEBANG" (see the _d_o_s_i_s_h_._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/> .
_I_M_P_O_R_T_A_N_T_!: 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.
CCaann II wwrriittee uusseeffuull PPeerrll pprrooggrraammss oonn tthhee ccoommmmaanndd lliinnee?? Yes. Read perlrun for more information. Some examples follow. (These assume standard Unix shell quoting rules.)
# sum first and last fields
perl -lane 'print $F[0] + $F[-1]' *
# identify text files
perl -le 'for(@ARGV) {print if -f && -T _}' *
# remove (most) comments from C program
perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
# make file a month younger than today, defeating reaper daemons
perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
# find first unused uid
perl -le '$i++ while getpwuid($i); print $i'
# display reasonable manpath
echo $PATH | perl -nl -072 -e '
s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
OK, the last one was actually an Obfuscated Perl Contest entry. :-)
WWhhyy ddoonn’’tt PPeerrll oonnee--lliinneerrss wwoorrkk oonn mmyy DDOOSS//MMaacc//VVMMSS ssyysstteemm?? The problem is usually that the command interpreters on those systems have rather different ideas about quoting than the Unix shells under which the one-liners were created. On some systems, you may have to change single-quotes to double ones, which you must _N_O_T do on Unix or Plan9 systems. You might also have to change a single % to a %%.
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 qqqq(()), q(), and qqxx(()), instead of "double quotes", 'single quotes',
and `backticks`, may make one-liners easier to write.
There is no general solution to all of this. It is a mess.
[Some of this answer was contributed by Kenneth Albanowski.]
WWhheerree ccaann II lleeaarrnn aabboouutt CCGGII oorr WWeebb pprrooggrraammmmiinngg iinn PPeerrll?? For modules, get the CGI or LWP modules from CPAN. For textbooks, see the two especially dedicated to web stuff in the question on books. For problems and questions related to the web, like “Why do I get 500 Errors” or “Why doesn’t it run from the browser right when it runs fine on the command line”, see the troubleshooting guides and references in perlfaq9 or in the CGI MetaFAQ:
L<http://www.perl.org/CGI_MetaFAQ.html>
Looking into <https://plackperl.org> 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.
WWhheerree ccaann II lleeaarrnn aabboouutt oobbjjeecctt--oorriieenntteedd PPeerrll pprrooggrraammmmiinngg?? A good place to start is perlootut, and you can use perlobj for reference.
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.
WWhheerree ccaann II lleeaarrnn aabboouutt lliinnkkiinngg CC wwiitthh PPeerrll?? 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.
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.
II’’vvee rreeaadd ppeerrlleemmbbeedd,, ppeerrllgguuttss,, eettcc..,, bbuutt II ccaann’’tt eemmbbeedd ppeerrll iinn mmyy CC pprrooggrraamm;; wwhhaatt aamm II ddooiinngg wwrroonngg?? Download the ExtUtils::Embed kit from CPAN and run `make test’. If the tests pass, read the pods again and again and again. If they fail, submit a bug report to https://github.com/Perl/perl5/issues with the output of “make test TEST_VERBOSE=1” along with “perl -V”.
WWhheenn II ttrriieedd ttoo rruunn mmyy ssccrriipptt,, II ggoott tthhiiss mmeessssaaggee.. WWhhaatt ddooeess iitt mmeeaann?? A complete list of Perl’s error messages and warnings with explanatory text can be found in perldiag. You can also use the splain program (distributed with Perl) to explain the error messages:
perl program 2>diag.out
splain [-v] [-p] diag.out
or change your program to explain the messages for you:
use diagnostics;
or
use diagnostics -verbose;
WWhhaatt’’ss MMaakkeeMMaakkeerr?? (contributed by brian d foy)
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.
AAUUTTHHOORR AANNDD CCOOPPYYRRIIGGHHTT #
Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and other
authors as noted. 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.
perl v5.36.3 2023-02-15 PERLFAQ3(1)