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Inline - Write Perl subroutines in other programming languages.


    use Inline C;
    print "9 + 16 = ", add(9, 16), "\n";
    print "9 - 16 = ", subtract(9, 16), "\n";
    int add(int x, int y) {
      return x + y;
    int subtract(int x, int y) {
      return x - y;


The Inline module allows you to put source code from other programming languages directly "inline" in a Perl script or module. The code is automatically compiled as needed, and then loaded for immediate access from Perl.

Inline saves you from the hassle of having to write and compile your own glue code using facilities like XS or SWIG. Simply type the code where you want it and run your Perl as normal. All the hairy details are handled for you. The compilation and installation of your code chunks all happen transparently; all you will notice is the delay of compilation on the first run.

The Inline code only gets compiled the first time you run it (or whenever it is modified) so you only take the performance hit once. Code that is Inlined into distributed modules (like on the CPAN) will get compiled when the module is installed, so the end user will never notice the compilation time.

Best of all, it works the same on both Unix and Microsoft Windows. See Inline-Support for support information.

Why Inline?

Do you want to know "Why would I use other languages in Perl?" or "Why should I use Inline to do it?"? I'll try to answer both.

Why would I use other languages in Perl?

The most obvious reason is performance. For an interpreted language, Perl is very fast. Many people will say "Anything Perl can do, C can do faster". (They never mention the development time :-) Anyway, you may be able to remove a bottleneck in your Perl code by using another language, without having to write the entire program in that language. This keeps your overall development time down, because you're using Perl for all of the non-critical code.

Another reason is to access functionality from existing API-s that use the language. Some of this code may only be available in binary form. But by creating small subroutines in the native language, you can "glue" existing libraries to your Perl. As a user of the CPAN, you know that code reuse is a good thing. So why throw away those Fortran libraries just yet?

If you are using Inline with the C language, then you can access the full internals of Perl itself. This opens up the floodgates to both extreme power and peril.

Maybe the best reason is "Because you want to!". Diversity keeps the world interesting. TMTOWTDI!

Why should I use Inline to do it?

There are already two major facilities for extending Perl with C. They are XS and SWIG. Both are similar in their capabilities, at least as far as Perl is concerned. And both of them are quite difficult to learn compared to Inline.

There is a big fat learning curve involved with setting up and using the XS environment. You need to get quite intimate with the following docs:

 * perlxs
 * perlxstut
 * perlapi
 * perlguts
 * perlmod
 * h2xs
 * xsubpp
 * ExtUtils::MakeMaker

With Inline you can be up and running in minutes. There is a C Cookbook with lots of short but complete programs that you can extend to your real-life problems. No need to learn about the complicated build process going on in the background. You don't even need to compile the code yourself. Inline takes care of every last detail except writing the C code.

Perl programmers cannot be bothered with silly things like compiling. "Tweak, Run, Tweak, Run" is our way of life. Inline does all the dirty work for you.

Another advantage of Inline is that you can use it directly in a script. You can even use it in a Perl one-liner. With XS and SWIG, you always set up an entirely separate module. Even if you only have one or two functions. Inline makes easy things easy, and hard things possible. Just like Perl.

Finally, Inline supports several programming languages (not just C and C++). As of this writing, Inline has support for C, C++, Java, Python, Tcl, Assembler, and CPR. There are plans to add many more. See Inline-Support for details.

Using the Inline.pm Module

Inline is a little bit different than most of the Perl modules that you are used to. It doesn't import any functions into your namespace and it doesn't have any object oriented methods. Its entire interface (with two minor exceptions) is specified through the 'use Inline ...' command.

This section will explain all of the different ways to use Inline. If you want to begin using C with Inline immediately, see Inline::C-Cookbook.

The Basics

The most basic form for using Inline is:

    use Inline X => "X source code";

where 'X' is one of the supported Inline programming languages. The second parameter specifies the source code that you want to bind to Perl. The source code can be specified in many ways, but most commonly it's a quoted string. A handy way to write the string is to use Perl's "here document" style of quoting. Like this:

    use Inline X => <<'END_OF_X';
       X source code goes here.

The source code can also be specified as a filename, a reference to a subroutine that returns source code, or a reference to an array that contains lines of source code.

If you want to specify the source code in a Perl variable, remember that 'use' is a compile time directive, so you'll need to set that variable in a BEGIN block, before the use.

    BEGIN {
        $X = "X source code";
    use Inline X => $X;

An alternative to doing this is to specify the source code at run time using the 'Inline->bind()' method. (This is the one interface exception mentioned above) The bind() method takes the same arguments as 'use Inline ...'.

    use Inline;
    $X = "X source code";
    bind Inline X => $X;  # or Inline->bind(X => $X);

Alternate Syntaxes

Instead of specifying the source code as a here-document string, you may want to put it at the end of your script, after the __END__ statement. Then you can tell Inline to read it in from the DATA filehandle, like this:

    use Inline C => 'DATA';
    print "9 + 16 = ", add(9, 16), "\n";
    print "9 - 16 = ", subtract(9, 16), "\n";
    int add(int x, int y) {
      return x + y;
    int subtract(int x, int y) {
      return x - y;

This syntax makes use of the source-file keyword, 'DATA', and a special marker: __C__. 'C' is the programming language you are binding to. Inline will read through the DATA filehandle and look for the special marker. It will use everything up until the next marker or the end of the file.

NOTE: The 'DATA' keyword can be ommitted if there are no extra parameters following it.

If you are writing a module, you can also use the DATA section for POD and AutoLoader subroutines. Just be sure to put them before the first Inline marker. If you install the helper module Inline::Filters, you can even use POD inside your Inline code. You just have to specify a filter to strip it out.

You can also specify multiple Inline sections, possibly in different programming languages. Here is another example:

    # The module Foo.pm
    package Foo;
    use AutoLoader;
    use Inline C;
    use Inline C => DATA => FILTERS => 'Strip_POD';
    use Inline Python;
    sub marine {
        # This is an autoloaded subroutine
    =head1 External subroutines
    /* First C section */
    /* Second C section */
    =head1 My C Function
    Some POD doc.
    """A Python Section"""

With a module you need to use __DATA__ instead of __END__. An important thing to remember is that you need to have one "use Inline Foo => 'DATA'" for each "__Foo__" marker, and they must be in the same order. This allows you to apply different configuration options to each section.

NOTE: Versions of Inline prior to 0.30 suggested a syntax of:

    use Inline;
    Inline->import(C => <DATA>);

to read source code from the DATA filehandle. This syntax has been deprecated. It will still work, but you will get a warning. It will soon be removed from the syntax. Use the new syntax for getting source code from the DATA filehandle. If you really need to access Inline at run time, use the bind() method instead. This (supported) code would do the same thing as the deprecated syntax:

    use Inline;
    Inline->bind(C => [<DATA>]);

But the preferred practice is:

    use Inline C => 'DATA';

or just:

    use Inline C;

Configuration Options

Inline trys to do the right thing as often as possible. But sometimes you may need to override the default actions. This is easy to do. Simply list the Inline configuration options after the regular Inline parameters. All congiguration options are specified as (key, value) pairs.

    use Inline (C => 'DATA',
                DIRECTORY => './inline_dir',
                LIBS => '-lfoo',
                INC => '-I/foo/include',
                PREFIX => 'XXX_',
                NOWARN => 1,

You can also specify the configuration options on a separate Inline call like this:

    use Inline (C => Config =>
                DIRECTORY => './inline_dir',
                LIBS => '-lfoo',
                INC => '-I/foo/include',
                PREFIX => 'XXX_',
                NOWARN => 1,
    use Inline C => <<'END_OF_C_CODE';

The special keyword 'Config' tells Inline that this is a configuration-only call. No source code will be compiled or bound to Perl.

If you want to specify global configuration options that don't apply to a particular language, just leave the language out of the call. Like this:

    use Inline Config => DIRECTORY => './inline_dir';

The Config options are inherited and additive. You can use as many Config calls as you want. And you can apply different options to different code sections. When a source code section is passed in , Inline will apply whichever options have been specified up to that point. Here is a complex configuration example:

    use Inline (Config => 
                DIRECTORY => './inline_dir',
    use Inline (C => Config =>
                LIBS => '-lglobal',
    use Inline (C => 'DATA',         # First C Section
                LIBS => ['-llocal1', '-llocal2'],
    use Inline (Config => 
                NOWARN => 1,
    use Inline (Python => 'DATA',    # First Python Section
                LIBS => '-lmypython1',
    use Inline (C => 'DATA',         # Second C Section
                LIBS => [undef, '-llocal3'],

The first Config applies to all subsequent calls. The second Config applies to all subsequent C sections (but not Python sections). In the first C section, the external libraries global, local1 and local2 are used. (Most options allow either string or array ref forms, and do the right thing.) The Python section does not use the global library, but does use the same DIRECTORY, and has warnings turned off. The second C section only uses the local3 library. That's because a value of undef resets the additive behaviour.

The DIRECTORY and NOWARN options are generic Inline options. All other options are language specific. To find out what the C options do, see Inline::C.

NOTE - Versions of Inline prior to 0.30, used a module called Inline::Config to configure Inline. This module is no longer supported and will no longer work with Inline. If you have it installed, remove it from your system to avoid occasional warnings. Everything that you could do with Inline::Config is still possible through the new configuration syntax.

On and Off

If a particular config option has value options of 1 and 0, you can use the ENABLE and DISABLE modifiers. In other words, this:

    use Inline Config => 
               FORCE_BUILD => 1,
               CLEAN_AFTER_BUILD => 0;

could be reworded as

    use Inline Config =>
               ENABLE => FORCE_BUILD,
               DISABLE => CLEAN_AFTER_BUILD;

Playing 'with' Others

Inline has a special configuration syntax that tells it to get more configuration options from other Perl modules. Here is an example:

    use Inline with => 'Event';

This tells Inline to load the module Event.pm and ask it for configuration information. Since Event has a C API of its own, it can pass Inline all of the information it needs to be able to use Event C callbacks seamlessly.

That means that you don't need to specify the typemaps, shared libraries, include files and other information required to get this to work.

You can specify a single module or a list of them. Like:

    use Inline with => qw(Event Foo Bar);

Currently, Event is the only module that works with Inline.

Inline Shortcuts

Inline lets you set many configuration options from the command line. These options are called 'shortcuts'. They can be very handy, especially when you only want to set the options temporarily, for say, debugging.

For instance, to get some general information about your Inline code in the script Foo.pl, use the command:

    perl -MInline=INFO Foo.pl

If you want to force your code to compile, even if its already done, use:

    perl -MInline=FORCE Foo.pl

If you want to do both, use:

    perl -MInline=INFO -MInline=FORCE Foo.pl

or better yet:

    perl -MInline=INFO,FORCE Foo.pl


Inline needs a place to build your code and to install the results of the build. It uses a single directory named '.Inline/' under normal circumstances. If you create this directory in your home directory, the current directory or in the directory where your program resides, Inline will find and use it. You can also specify it in the environment variable PERL_INLINE_DIRECTORY or directly in your program, by using the DIRECTORY keyword option. If Inline cannot find the directory in any of these places it will create a '_Inline/' directory in either your current directory or the directory where your script resides.

One of the key factors to using Inline successfully, is understanding this directory. When developing code it is usually best to create this directory (or let Inline do it) in your current directory. Remember that there is nothing sacred about this directory except that it holds your compiled code. Feel free to delete it at any time. Inline will simply start from scratch and recompile your code on the next run. If you have several programs that you want to force to recompile, just delete your '.Inline/' directory.

It is probably best to have a separate '.Inline/' directory for each project that you are working on. You may want to keep stable code in the <.Inline/> in your home directory. On multi-user systems, each user should have their own '.Inline/' directories. It could be a security risk to put the directory in a shared place like /tmp/.

Debugging Inline Errors

All programmers make mistakes. When you make a mistake with Inline, like writing bad C code, you'll get a big error report on your screen. This report tells you where to look to do the debugging.

When Inline needs to build something it creates a subdirectory under your DIRECTORY/build/ directory. This is where it writes all the components it needs to build your extension. Things like XS files, Makefiles and output log files.

If everything goes OK, Inline will delete this subdirectory. If there is an error, Inline will leave the directory intact and print its location. The idea is that you are supposed to go into that directory and figure out what happened.

As a convenience, Inline copies your latest error directory to DIRECTORY/errors and strips all of the MD5 hash codes out of the names. More debugging improvements are coming in future releases.

Read the doc for your particular Inline language module for more information.

The 'config' Registry File

Inline keeps a cached file of all of the Inline Language Support Module's meta data in a file called config. This file can be found in your DIRECTORY directory. If the file does not exist, Inline creates a new one. It will search your system for any module beginning with Inline::. It will then call that module's register() method to get useful information for future invocations.

Whenever you add a new ILSM, you should delete this file so that Inline will auto-discover your newly installed language module.

Configuration Options

This section lists all of the generic Inline configuration options. For language specific configuration, see the doc for that language.


The DIRECTORY config option is the directory that Inline uses to both build and install an extension.

Normally Inline will search in a bunch of known places for a directory called '.Inline/'. Failing that, it will create a directory called '_Inline/'

If you want to specify your own directory, use this configuration option.

Note that you must create the DIRECTORY directory yourself. Inline will not do it for you.


WITH can also be used as a configuration option instead of using the special 'with' syntax. Do this if you want to use different sections of Inline code with different modules. (Probably a very rare usage)

    use Event;
    use Inline C => DATA => WITH => 'Event';

Modules specified using the config form of WITH will not be automatically required. You must use them yourself.


This option is for compiled languages only. It tells Inline to tell DynaLoader to load an object file in such a way that its symbols can be dynamically resolved by other object files. May not work on all platforms. See the GLOBAL shortcut below.


You must use this option whenever you use Perl's -T switch, for taint checking. This option tells Inline to blindly untaint all tainted variables. It also turns on SAFEMODE by default. See the UNTAINT shortcut below.


Perform extra safety checking, in an attempt to thwart malicious code. This option cannot guarantee security, but it does turn on all the currently implemented checks.

There is a slight startup penalty by using SAFEMODE. Also, using UNTAINT automatically turns this option on. If you need your code to start faster under -T (taint) checking, you'll need to turn this option off manually. Only do this if you are not worried about security risks. See the UNSAFE shortcut below.


Makes Inline build (compile) the source code every time the program is run. The default is 0. See the FORCE shortcut below.


Tells Inline to clean up the current build area if the build was successful. Sometimes you want to DISABLE this for debugging. Default is 1. See the NOCLEAN shortcut below.


Tells Inline to clean up the old build areas within the entire Inline DIRECTORY. Default is 0. See the CLEAN shortcut below.

Tells Inline to print various information about the source code. Default is 0. See the INFO shortcut below.

Tells Inline to print Version info about itself. Default is 0. See the VERSION shortcut below.


Puts Inline into 'REPORTBUG' mode, which is what you want if you desire to report a bug.


This option tells Inline to turn off any warnings.

NOTE: It is NOT yet implemented.

Inline Configuration Shortcuts

This is a list of all the shorcut configuration options currently available for Inline. Specify them from the command line when running Inline scripts.

    perl -MInline=NOCLEAN inline_script.pl


    perl -MInline=Info,force,NoClean inline_script.pl

You can specify multiple shortcuts separated by commas. They are not case sensitive. You can also specify shorcuts inside the Inline program like this:

    use Inline 'Info', 'Force', 'Noclean';

NOTE: If a 'use Inline' statement is used to set shortcuts, it can not be used for additional purposes.


Tells Inline to remove any build directories that may be lying around in your build area. Normally these directories get removed immediately after a successful build. Exceptions are when the build fails, or when you use the NOCLEAN or REPORTBUG options.


Forces the code to be recompiled, even if everything is up to date.


Turns on the GLOBAL_LOAD option.


This is a very useful option when you want to know what's going on under the hood. It tells Inline to print helpful information to STDERR. Among the things that get printed is a list of which Inline functions were successfully bound to Perl.


Tells Inline to leave the build files after compiling.


Puts Inline into 'REPORTBUG' mode, which does special processing when you want to report a bug. REPORTBUG also automatically forces a build, and doesn't clean up afterwards. This is so that you can tar and mail the build directory to me. REPORTBUG will print exact instructions on what to do. Please read and follow them carefully.

NOTE: REPORTBUG informs you to use the tar command. If your system does not have tar, please use the equivalent zip command.


Turns SAFEMODE on. UNTAINT will turn this on automatically. While this mode performs extra security checking, it does not guarantee safety.


Says that compiled code should be installed in the Perl installation's "site_perl" directory. Use this to permanently install an Inlined module.

This is the one shortcut that is not normally used from the command line. You put a line like this at the top of a 'test.pl':

    use Inline SITE_INSTALL;

This causes 'make test' to put the compiled results in the right place.


Turns SAFEMODE off. Use this in combination with UNTAINT for slightly faster startup time under -T. Only use this if you are sure the environment is safe.


Turn the UNTAINT option on. Used with -T switch.


Tells Inline to report it's release version. Program will exit immediately after version is printed.

Writing Modules with Inline

Writing CPAN modules that use other programming languages is easy with Inline. Let's say that you wanted to write a module called Math::Simple. Start by using the following command:

    h2xs -AXn Math::Simple

This will generate a bunch of files that form a skeleton of what you need for a distributable module. Next, modify the Simple.pm file to look like this:

    package Math::Simple;
    use strict;
    use vars qw($VERSION @ISA @EXPORT_OK);
    require Exporter;
    @ISA = qw(Exporter);
    @EXPORT_OK = qw(add subtract);
    BEGIN {
        $VERSION = '0.01';
    use Inline C => 'DATA';
    int add(int x, int y) {
      return x + y;
    int subtract(int x, int y) {
      return x - y;

Finally, you need to add the following line to the top of your test.pl file:

    use Inline SITE_INSTALL;

When the person installing Math::Simple does a "make test", the Inline module will compile the Inlined code and place the executable code into the ./blib directory. Then when a "make install" is done, the module will be copied into Perl's $Config{installsitearch} directory (which is where an installed module should go).

Now all you need to do is:

    perl Makefile.PL
    make dist

That will generate the file Math-Simple-0.01.tar.gz which is a distributable package.

IMPORTANT NOTE: It has been determined that creating modules for CPAN using the above technique is doable, but not optimal. The basic problem is that there is no way to automatically remove old executable objects on subsequent releases. There are also some additional subtle problems. So, my official stance is to not use Inline for CPAN modules until Inline release 0.40 or greater. These issues will be resolved at that release level. This technique is still perfectly fine for personal use, if your not too concerned about have a few harmless artifacts in your site lib tree.

How Inline Works

In reality, Inline just automates everything you would need to do if you were going to do it by hand (using XS, etc).

Inline performs the following steps:

1) Receive the Source Code

Inline gets the source code from your script or module with a statements like the following:

    use Inline C => "Source-Code";


    use Inline;
    bind Inline C => "Source-Code";

where C is the programming language of the source code, and Source-Code is a string, a file name, an array reference, or the special 'DATA' keyword.

Since Inline is coded in a "use" statement, everything is done during Perl's compile time. If anything needs to be done that will affect the Source-Code, it needs to be done in a BEGIN block that is before the "use Inline ..." statement. If you really need to specify code to Inline at runtime, you can use the bind() method.

Source code that is stowed in the 'DATA' section of your code, is read in by an INIT subroutine in Inline. That's because the DATA filehandle is not available at compile time.

2) Check if the Source Code has been Built

Inline only needs to build the source code if it has not yet been built. It accomplishes this seemingly magical task in an extremely simple and straightforward manner. It runs the source text through the Digest::MD5 module to produce a 128-bit "fingerprint" which is virtually unique. The fingerprint (in hex) is mangled with the current package name (and the script name, if the package is "main") along with the name of the programming language, to form a unique name for the executable module. For instance, the C code from examples/example001.pl (see "Examples In C") would mangle into:


If an executable with that name already exists, then proceed to step 8. (No compilation is necessary)

3) Find a Place to Build and Install

At this point Inline knows it needs to build the source code. The first thing to figure out is where to create the great big mess associated with compilation, and where to put the object when it's done.

By default Inline will try to build and install under the first place that meets one of the following conditions:

    A) The DIRECTORY= config option; if specified
    B) The PERL_INLINE_DIRECTORY environment variable; if set
    C) .Inline/ (in current directory); if exists and $PWD != $HOME
    D) bin/.Inline/ (in directory of your script); if exists
    E) ~/.Inline/; if exists
    F) ./_Inline/; if exists
    G) bin/_Inline; if exists
    H) Create ./_Inline/; if possible
    I) Create bin/_Inline/; if possible

Failing that, Inline will croak. This is rare and easily remedied by just making a directory that Inline will use;

If the SITE_INSTALL option is in effect, then Inline will only use ./_Inline/ to build in, and the $Config{installsitearch} directory to install the executable in. This option is intended to be used in modules that are to be distributed on the CPAN, so that they get installed in the proper place.

4) Parse the Source for Semantic Cues

Inline::C uses the module Parse::RecDescent to parse through your chunks of C source code and look for things that it can create run-time bindings to. In C it looks for all of the function definitions and breaks them down into names and data types. These elements are used to correctly bind the C function to a Perl subroutine. Other Inline languages like Python and Java actually use the python and javac modules to parse the Inline code.

5) Create the Build Environment

Now Inline can take all of the gathered information and create an environment to build your source code into an executable. Without going into all the details, it just creates the appropriate directories, creates the appropriate source files including an XS file (for C) and a Makefile.PL.

6) Build the Code and Install the Executable

The planets are in alignment. Now for the easy part. Inline just does what you would do to install a module. "perl Makefile.PL && make && make test && make install". If something goes awry, Inline will croak with a message indicating where to look for more info.

7) Tidy Up

By default, Inline will remove all of the mess created by the build process, assuming that everything worked. If the build fails, Inline will leave everything intact, so that you can debug your errors. Setting the NOCLEAN shortcut option will also stop Inline from cleaning up.

8) DynaLoad the Executable

For C (and C++), Inline uses the DynaLoader::bootstrap method to pull your external module into Perl space. Now you can call all of your external functions like Perl subroutines.

Other languages like Python and Java, provide their own loaders.


For information about using Inline with C see Inline::C.

For sample programs using Inline with C see Inline::C-Cookbook.

For information on supported languages and platforms see Inline-Support.

For information on writing your own Inline Language Support Module, see Inline-API.

Inline's mailing list is inline@perl.org

To subscribe, send email to inline-subscribe@perl.org


When reporting a bug, please do the following:

 - Put "use Inline REPORTBUG;" at the top of your code, or
   use the command line option "perl -MInline=REPORTBUG ...".
 - Run your code.
 - Follow the printed directions.

Here are some things to watch out for:

  1. While Inline does attempt to clean up after itself, there is currently no functionality to remove a shared object when a new version is compiled. This will be addressed in version 0.40 and higher.


Brian Ingerson <INGY@cpan.org>

Neil Watkiss <NEILW@cpan.org> is the author of Inline::CPP, Inline::Python, Inline::ASM, Inline::Struct and Inline::Filters. He is known in the innermost Inline circles as the "Boy Wonder".


Copyright (c) 2000, 2001. Brian Ingerson. All rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

See http://www.perl.com/perl/misc/Artistic.html