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PERLFAQ3(1pm)          Perl Programmers Reference Guide          PERLFAQ3(1pm)




NAME

       perlfaq3 - Programming Tools


VERSION

       version 5.021010


DESCRIPTION

       This section of the FAQ answers questions related to programmer tools
       and programming support.

   How do I do (anything)?
       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.

   How can I use Perl interactively?
       The typical approach uses the Perl debugger, described in the
       perldebug(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.

   How do I find which modules are installed on my system?
       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.)

   How do I debug my Perl programs?
       (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).

   How do I profile my Perl programs?
       (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 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> .

   How do I cross-reference my Perl programs?
       The B::Xref module can be used to generate cross-reference reports for
       Perl programs.

           perl -MO=Xref[,OPTIONS] scriptname.plx

   Is there a pretty-printer (formatter) for Perl?
       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 .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>

   Is there an IDE or Windows Perl Editor?
       Perl programs are just plain text, so any editor will do.

       If you're on Unix, you already have an IDE--Unix itself. The Unix
       philosophy is the philosophy of several small tools that each do one
       thing and do it well. It's like a carpenter's toolbox.

       If you want 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.

       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://dickey.his.com/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/> ).

   Where can I get Perl macros for vi?
       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/> .

   Where can I get perl-mode or cperl-mode for emacs?
       Since Emacs version 19 patchlevel 22 or so, there have been both a
       perl-mode.el and support for the Perl debugger built in. These should
       come with the standard Emacs 19 distribution.

       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>

   How can I use curses with Perl?
       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.gz>
       ; this program repeats a command and updates the screen as needed,
       rendering rep ps axu similar to top.

   How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
       (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.

   How can I make my Perl program run faster?
       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).

       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.

   How can I make my Perl program take less memory?
       When it comes to time-space tradeoffs, Perl nearly always prefers to
       throw memory at a problem. Scalars in Perl use more memory than strings
       in C, arrays take more than that, and hashes use even more. While
       there's still a lot to be done, recent releases have been addressing
       these issues. For example, as of 5.004, duplicate hash keys are shared
       amongst all hashes using them, so require no reallocation.

       In some cases, using substr() or vec() to simulate arrays can be highly
       beneficial. For example, an array of a thousand booleans will take at
       least 20,000 bytes of space, but it can be turned into one 125-byte bit
       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 (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.

   Is it safe to return a reference to local or lexical data?
       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";

   How can I free an array or hash so my program shrinks?
       (contributed by Michael Carman)

       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?"

   How can I make my CGI script more efficient?
       Beyond the normal measures described to make general Perl programs
       faster or smaller, a CGI program has additional issues. It may be run
       several times per second. Given that each time it runs it will need to
       be re-compiled and will often allocate a megabyte or more of system
       memory, this can be a killer. Compiling into C isn't going to help you
       because the process start-up overhead is where the bottleneck is.

       There are 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/>
       .

   How can I hide the source for my Perl program?
       Delete it. :-) Seriously, there are a number of (mostly unsatisfactory)
       solutions with varying levels of "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 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.

   How can I compile my Perl program into byte code or C?
       (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 ( <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.

   How can I get "#!perl" to work on [MS-DOS,NT,...]?
       For OS/2 just use

           extproc perl -S -your_switches

       as the first line in "*.cmd" file ("-S" due to a bug in cmd.exe's
       "extproc" handling). For DOS one should first invent a corresponding
       batch file and codify it in "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.

   Can I write useful Perl programs on the command line?
       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. :-)

   Why don't Perl one-liners work on my DOS/Mac/VMS system?
       The problem is usually that the command interpreters on those systems
       have rather different ideas about quoting than the Unix shells under
       which the one-liners were 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 (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.]

   Where can I learn about CGI or Web programming in Perl?
       For modules, get the CGI or LWP modules from CPAN. For textbooks, see
       the two especially dedicated to web stuff in the question on books. For
       problems and questions related to the web, like "Why do I get 500
       Errors" or "Why doesn't it run from the browser right when it runs fine
       on the command line", see the troubleshooting guides and references in
       perlfaq9 or in the CGI MetaFAQ:

           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.

   Where can I learn about object-oriented Perl programming?
       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.

   Where can I learn about linking C with Perl?
       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.

   I've read perlembed, perlguts, etc., but I can't embed perl in my C
       program; what am I doing wrong?
       Download the ExtUtils::Embed kit from CPAN and run `make test'. If the
       tests pass, read the pods again and again and again. If they fail, see
       perlbug and send a bug report with the output of "make test
       TEST_VERBOSE=1" along with "perl -V".

   When I tried to run my script, I got this message. What does it mean?
       A complete list of Perl's error messages and warnings with explanatory
       text can be found in 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;

   What's MakeMaker?
       (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.


AUTHOR AND COPYRIGHT

       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 v5.24.0                      2016-03-01                     PERLFAQ3(1pm)

perl 5.24 - Generated Sat Dec 3 10:53:46 CST 2016
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