PERLFAQ3(1perl)

📦
version 5.44.0 · 2 versions
, in arch rolling

🌸 NAME 🌸

perlfaq3 — Programming Tools 💅 This is PERLFAQ3(1perl) from the Perl Programmers Reference Guide, bestie. No cap.

✨ VERSION ✨

version 5.20250619

💖 DESCRIPTION 💖

This section of the FAQ answers questions related to programmer tools and programming support. So like, everything you need for your dev setup vibe check. 🫶

🦋 How do I do (anything)? 🦋

okay so bestie, 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

A crude table of contents for the Perl manpage set is found in perltoc. iykyk 💅

🧚 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. main character energy ✨

🔍 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 a while 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.) lowkey iconic 🍓

🐛 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). not me debugging with print again 😭

📊 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", <https://drdobbs.com/creating-a-perl-debugger/184404522> , and "Profiling in Perl" <https://drdobbs.com/profiling-in-perl/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 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> . no cap, this is obsessed-worthy 🔥

🔗 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 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/T/TO/TOMC/scripts/toms.exrc.gz> ate 💅

🖥️ 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):

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.

periodt. 💜

OptiPerl is a Windows IDE with a whole simulated CGI environment baked in, plus a debugger and a syntax-highlighting editor. 💅

Padre is a cross-platform IDE for Perl, and it's written in Perl using wxWidgets so it gives you that native look and feel. Open source under the Artistic License, and it's 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.

okay so for editors, real talk: if you're on Unix you probably already have vi or a vi clone, and possibly an emacs too, so you might not even need to download anything. In any emacs the cperl-mode (M-x cperl-mode) gives you arguably the best available Perl editing mode in any editor, fr fr. 🧚

If you're on Windows, use any editor that works with plain text, like NotePad or WordPad. Word processors like Microsoft Word or WordPerfect typically do not work because they insert all sorts of behind-the-scenes info — though some do let you save files as "Text Only". You can also download text editors made specifically for programming, like Textpad ( <http://www.textpad.com/> ) and UltraEdit ( <http://www.ultraedit.com/> ), among others.

If you're on MacOS, 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's also a toyedit Text widget based editor written in Perl that ships 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. And 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.

🌸 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/id/T/TO/TOMC/scripts/toms.exrc.gz> — it's 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's been both a perl-mode.el and support for the Perl debugger built in. These should come with the standard Emacs 19 distribution.

heads up bestie: the perl-mode of emacs will have fits with "main'foo" (single quote), and it messes up the indentation and highlighting. You're probably using "main::foo" in new Perl code anyway, so this shouldn't be an issue. 💅

For CPerlMode, see <https://www.emacswiki.org/emacs/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/id/T/TO/TOMC/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 it just refers 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!

Okay so bestie, the number one glow-up for your memory usage: do not slurp the whole file when you can just vibe through it line by line. 💅

Concretely, do this:

#
# Good Idea
#
while (my $line = <$file_handle>) {
   # ...
}

and NOT this:

#
# Bad Idea
#
my @data = <$file_handle>;
foreach (@data) {
    # ...
}

When the files are tiny, it literally does not matter which one you pick, no cap. But the second they start getting large, the difference is giving main character energy. 🦋

Use map and grep selectively

Remember, bestie, that both map and grep want a LIST as their argument. So if you do this:

@wanted = grep {/pattern/} <$file_handle>;

you just slurped the ENTIRE file into memory and you didn't even mean to 😭. For big files, loop instead:

while (<$file_handle>) {
        push(@wanted, $_) if /pattern/;
}

Avoid unnecessary quotes and stringification

Don't quote big strings unless you literally have to:

my $copy = "$large_string";

This makes 2 copies of $large_string (one for $copy, and another one just for the quotes 🙈), whereas:

my $copy = $large_string;

only makes one copy. Slay.

Same energy for stringifying giant arrays:

{
local $, = "\n";
print @big_array;
}

is so much more memory-efficient than either of these:

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 — and this is the iconic part — it's the only way to pass multiple lists or hashes (or both!) in a single call or return. It also skips making a whole copy of everything. ✨

That said, use some judgement, because any changes you make will propagate back to the original data. If you genuinely want to mangle (er, modify, bestie) a copy, you're gonna have to pay the memory cost of making one.

Tie large variables to disk

For "big" data stores — like, ones that are literally bigger than your available memory 👀 — think about using one of the DB modules to keep it on disk instead of in RAM. Yeah it's slower to access, but that's genuinely better than letting your hard disk thrash from massive swapping. 💀

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

Yes bestie. Perl's garbage collection system has this handled, so everything just works out right. Periodt.

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)

Short answer: you usually can't. 😭 Memory allocated to lexicals (i.e. my() variables) cannot be reclaimed or reused, even when they go out of scope. It's reserved, just in case those variables come back into scope. Memory given to global variables can be reused (within your program) by using undef() and/or delete().

On most operating systems, memory a program has grabbed can never be handed back to the system. That's exactly why long-running programs sometimes re-exec themselves. Some operating systems (notably, the ones that use mmap(2) to allocate big chunks of memory) can reclaim memory that's no longer in use — but on those systems, perl has to be configured and compiled to use the OS's malloc, not perl's own.

And honestly? In general, memory allocation and de-allocation isn't something you can or should be stressing about in Perl. Lowkey let it go. 🧚

See also "How can I make my Perl program take less memory?"

How can I make my CGI script more efficient?

Beyond all the normal stuff for making general Perl programs faster or smaller, a CGI program has extra problems. It might get run several times per second. And every single time it runs, it needs to be re-compiled and will often grab a megabyte or more of system memory — which can be a total killer. Compiling it into C won't save you either, because the bottleneck is the process start-up overhead, fr fr.

There are three popular ways to dodge this overhead.

  1. One solution is running the Apache HTTP server (available from <http://www.apache.org/> ) with either the mod_perl or mod_fastcgi plugin modules.

With mod_perl and the Apache::Registry module (distributed with mod_perl), httpd runs with an embedded Perl interpreter which pre-compiles your script and then executes it inside 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 basically anything a module written in C can. For more on mod_perl, see <http://perl.apache.org/>

  1. 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.
  2. Finally, Plack is a Perl module and toolkit containing PSGI middleware, helpers and adapters to web servers. It lets you easily deploy scripts that keep running, and gives you flexibility about which web server you use. It can let existing CGI scripts enjoy that flexibility and performance with minimal changes, or it can be used alongside modern Perl web frameworks to make writing and deploying web services with Perl an absolute breeze. 🍓

These solutions can have far-reaching effects on your system and on the way you write your CGI programs, so please 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. :-) No but seriously, there are a bunch of (mostly unsatisfactory) solutions with varying levels of "security". 🙃

First things first though: you can't take away read permission, because the source code has to be readable to be compiled and interpreted. (That doesn't mean a CGI script's source is readable by everyone on the web though — only by people with access to the filesystem.) So you're stuck leaving the permissions at the socially friendly 0755 level.

Some people treat this as a security problem. But listen: if your program does insecure things and relies on people not knowing how to exploit them, it is not secure. It's often perfectly possible for someone to figure out the insecure bits and exploit them without ever viewing your source. "Security through obscurity" — the name for hiding your bugs instead of fixing them — is little security indeed. 💀

You can try 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 can decrypt it. You can try the byte code compiler and interpreter described later in perlfaq3, but the curious can probably de-compile it anyway. You can try the native-code compiler described later, but crackers might disassemble it. These all pose varying degrees of difficulty to someone who wants your code — but none of them can definitively conceal it. (Which is true of every language, not just Perl, btw.)

It is very easy to recover the source of Perl programs. You literally just 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 — not a Perl-only problem.

If what you're actually worried about is people profiting off your code, then the bottom line is this: 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, obviously, so 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 work 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 just bundle a Perl interpreter into 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.

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 a *.cmd file (-S is there because of a bug in cmd.exe's extproc handling). For DOS, you 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 a different port — maybe even building your own Win95/NT Perl from the standard sources 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 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 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"}'

okay so that last one? literally an Obfuscated Perl Contest entry. :-) not me sobbing 😭 but also it ate. 💅

💀 Why don't Perl one-liners work on my DOS/Mac/VMS system? 💀

bestie, the tea is: those systems' command interpreters have totally different opinions about quoting than the Unix shells where these one-liners were born. on some systems you might have to switch single-quotes to double ones — but you must NOT do that on Unix or Plan9 systems, fr fr. you might also have to change a single % to %%.

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. 😭

shoutout to Kenneth Albanowski for contributing some of this answer! 💖

🌐 Where can I learn about CGI or Web programming in Perl? 🌐

for modules? grab the CGI or LWP modules from CPAN, bestie. for textbooks, check the two that are especially dedicated to web stuff in the question on books. and for web problems/questions 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", go look at the troubleshooting guides and references in perlfaq9 or in the CGI MetaFAQ:

L<http://www.perl.org/CGI_MetaFAQ.html>

also? 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, periodt.

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

a good place to start is perlootut, and you can use perlobj for reference, no cap.

a good book on OO on Perl is "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. iconic tbh.

🔗 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, submit a bug report to https://github.com/Perl/perl5/issues 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.

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.

💖 that's the whole vibe from perl v5.44.0, dated 2026-10-17 — PERLFAQ3(1perl), mwah! stay slaying, bestie! 💅

📦 where this page comes from