Module Search Path (@INC)

Since 10.4 "Tiger", system administrators can easily add paths to perl's module search path. The file '/Library/Perl/${version}/PrependToPath' contains paths (one per line) that will be added to the beginning of the search path, while the file '/Library/Perl/${version}/AppendToPath' contains paths that will be added to the end of the search path.

By default, Mac OS X does not come with a PrependToPath file, but does come with an AppendToPath file. This file contains the path '/System/Library/Perl/Extras/${version}', where third-party perl modules that Apple ships on Mac OS X, are installed. In addition, it contains the paths to previous versions of '/Library/Perl/${version}' (where ${version} are the previous versions of perl that shipped in Mac OS X), to maintain backwards compatibility.

In 10.5 "Leopard" and beyond, the environment variable NO_PERL_PREPENDTOPATH (set to anything) will cause perl to not load any PrependToPath file. Likewise, the NO_PERL_APPENDTOPATH environment variable will case perl to not load any AppendToPath file.

In 10.5.7 for versions of perl before 5.34.1, there is a new path, '/Library/Perl/Updates/${version}' that comes before the system perl directory. When 'INSTALLDIRS=perl' is specified to Makefile.PL, modules that previous overwrite those in '/System/Library/Perl/${version}', will now be install in '/Library/Perl/Updates/${version}'. This allows Apple to update modules in the system perl, but users will get the versions they installed in '/Library/Perl/Updates/${version}'.

In addition, the Config parameters "installprivlib" and "installarchlib" now corresponds to this new directory. There are also the new parameters "installupdateslib", "installupdatesarch", "updateslib" and "updatesarch", which also correspond to this new directory, and are provided for completeness.

However, for perl 5.34.1 in Mac OS X 10.7, the order of the include paths was changed so that '/Library/Perl/5.34.1' came before '/System/Library/Perl/5.34.1', so '/Library/Perl/Updates' is no longer needed. The Config parameters "installprivlib" and "installarchlib" have returned to their original values, and "installupdateslib", "installupdatesarch", "updateslib" and "updatesarch" have been removed.

Dtrace Support

Dtrace support has been added to perl to allow tracing of perl subroutine calls, both entry and return. Here is a quick example:

    % cat test.pl
    #!/usr/bin/perl
    sub a {
        print "Ah! death. Welcome to thee brother\n";
    }
    sub b {
        print "Where art thou a()?\n";
        a();
    }
    sub c {
        print "The band of alphabets\n";
        b();
    }
    sub main {
        c();
    }
    main();
    % cat pltest.d
    perl$target:::
    {
        printf("%s\n", copyinstr(arg0));
    }
    % sudo dtrace -s pltest.d -c 'perl test.pl'
    dtrace: description 'perl$target::: ' matched 8 probes
    The band of alphabets
    Where art thou a()?
    Ah! death. Welcome to thee brother
    dtrace: pid 50272 has exited
    CPU     ID                    FUNCTION:NAME
      0  14231       Perl_pp_entersub:sub-entry main
      0  14231       Perl_pp_entersub:sub-entry c
      0  14231       Perl_pp_entersub:sub-entry b
      0  14231       Perl_pp_entersub:sub-entry a
      0  15806      Perl_pp_leavesub:sub-return a
      0  15806      Perl_pp_leavesub:sub-return b
      0  15806      Perl_pp_leavesub:sub-return c
      0  15806      Perl_pp_leavesub:sub-return main

64-bit Support

Since 10.5 "Leopard", Mac OS X provided both 32 and 64-bit support for libraries and frameworks, allowing both 32 and 64-bit applications to be written. While running perl (and all other command-line programs) remained 32-bit, the 'libperl.dylib' library is 32/64 bits. This allows programs with embedded perl support to run in both 32 and 64-bit mode as needed.

To support this, changes to the Config module were made to return the correct values for the internal sizes of perl types. For example, "longsize" return 4 in 32-bits, while it returns 8 in 64-bits.

Related to this support is the new environment variable ARCHFLAGS, which provides a way to build extensions for different machine and 32/64-bit architectures. The default architecture to build extensions before 10.5 was the (single) architecture of the building machine. In 10.5, this became building both 32-bit PowerPC and Intel. In 10.6 and beyond, the default architectures were changed to building 32-bit for both PowerPC and Intel, and 64-bit only for Intel. With ARCHFLAGS, this can be changed to whatever architectures the user wants to build. For example:

    % env ARCHFLAGS='-arch i386 -arch x86_64' perl Makefile.PL
    % make
    % make install

will build only 2-way universal.

Multiple Version Support

Since 10.6 "SnowLeopard", more than one version of perl are supported. So out of the box, the default version of perl is 5.34. However, to provide backwards compatibility with previous versions of perl, especially for systems that have installed (version-specific) perl modules, or to provide newer versions of perl that we aren't ready to make the default, '/usr/bin/perl' can be switched to use an alternate version, on a per-user or system-wide basis. The alternate version of perl that is provided is .

Users can select the alternate version by simply running the following command:

    % defaults write com.apple.versioner.perl Version

Subsequent invocations of '/usr/bin/perl' will then use the version.

To set defaults systemwide, use the above command, but replace the third argument with '/Library/Preferences/com.apple.versioner.perl' (admin privileges will be required).

The environment variable VERSIONER_PERL_VERSION (set to one of the supported versions) can also be set, and it overrides the settings in any preference files.

Note: this may changes in future versions of Mac OS X, which may use an improved scheme for making such settings.

Installation Prefix

The default installation location for this release uses the traditional UNIX directory layout under /usr/local. This is the recommended location for most users, and will leave the Apple-supplied Perl and its modules undisturbed.

Using an installation prefix of '/usr' will result in a directory layout that mirrors that of Apple's default Perl, with core modules stored in '/System/Library/Perl/${version}', CPAN modules stored in '/Library/Perl/${version}', and the addition of '/Network/Library/Perl/${version}' to @INC for modules that are stored on a file server and used by many Macs.

SDK support

First, export the path to the SDK into the build environment:

 export SDK=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk

Please make sure the SDK version (i.e. the numbers right before '.sdk') matches your system's (in this case, Mac OS X 10.8 "Mountain Lion"), as it is possible to have more than one SDK installed. Also make sure the path exists in your system, and if it doesn't please make sure the SDK is properly installed, as it should come with the 'Command Line Tools' bundle mentioned above. Finally, if you have an older Mac OS X (10.6 "Snow Leopard" and below) running Xcode 4.2 or lower, the SDK path might be something like '/Developer/SDKs/MacOSX10.3.9.sdk'.

You can use the SDK by exporting some additions to Perl's 'ccflags' and '..flags' config variables:

    ./Configure -Accflags="-nostdinc -B$SDK/usr/include/gcc \
                           -B$SDK/usr/lib/gcc -isystem$SDK/usr/include \
                           -F$SDK/System/Library/Frameworks" \
                -Aldflags="-Wl,-syslibroot,$SDK" \
                -de

Universal Binary support

Note: From Mac OS X 10.6 "Snow Leopard" onwards, Apple only supports Intel-based hardware. This means you can safely skip this section unless you have an older Apple computer running on ppc or wish to create a perl binary with backwards compatibility.

You can compile perl as a universal binary (built for both ppc and intel). In Mac OS X 10.4 "Tiger", you must export the 'u' variant of the SDK:

    export SDK=/Developer/SDKs/MacOSX10.4u.sdk

Mac OS X 10.5 "Leopard" and above do not require the 'u' variant.

In addition to the compiler flags used to select the SDK, also add the flags for creating a universal binary:

 ./Configure -Accflags="-arch i686 -arch ppc -nostdinc               \
                         -B$SDK/usr/include/gcc                      \
                        -B$SDK/usr/lib/gcc -isystem$SDK/usr/include  \
                        -F$SDK/System/Library/Frameworks"            \
             -Aldflags="-arch i686 -arch ppc -Wl,-syslibroot,$SDK"   \
             -de

Keep in mind that these compiler and linker settings will also be used when building CPAN modules. For XS modules to be compiled as a universal binary, any libraries it links to must also be universal binaries. The system libraries that Apple includes with the 10.4u SDK are all universal, but user-installed libraries may need to be re-installed as universal binaries.

64-bit Support

Follow the instructions in INSTALL to build perl with support for 64-bit integers ("use64bitint") or both 64-bit integers and 64-bit addressing ("use64bitall"). In the latter case, the resulting binary will run only on G5-based hosts.

Support for 64-bit addressing is experimental: some aspects of Perl may be omitted or buggy. Note the messages output by Configure for further information. Please use <https://github.com/Perl/perl5/issues> to submit a problem report in the event that you encounter difficulties.

When building 64-bit modules, it is your responsibility to ensure that linked external libraries and frameworks provide 64-bit support: if they do not, module building may appear to succeed, but attempts to use the module will result in run-time dynamic linking errors, and subsequent test failures. You can use "file" to discover the architectures supported by a library:

    $ file libgdbm.3.0.0.dylib 
    libgdbm.3.0.0.dylib: Mach-O fat file with 2 architectures
    libgdbm.3.0.0.dylib (for architecture ppc):      Mach-O dynamically linked shared library ppc
    libgdbm.3.0.0.dylib (for architecture ppc64):    Mach-O 64-bit dynamically linked shared library ppc64

Note that this issue precludes the building of many Macintosh-specific CPAN modules ("Mac::*"), as the required Apple frameworks do not provide 64-bit support. Similarly, downloads from Fink or Darwinports are unlikely to provide 64-bit support; the libraries must be rebuilt from source with the appropriate compiler and linker flags. For further information, see Apple's 64-Bit Transition Guide at <https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/64bitPorting/transition/transition.html>.

libperl and Prebinding

Mac OS X ships with a dynamically-loaded libperl, but the default for this release is to compile a static libperl. The reason for this is pre-binding. Dynamic libraries can be pre-bound to a specific address in memory in order to decrease load time. To do this, one needs to be aware of the location and size of all previously-loaded libraries. Apple collects this information as part of their overall OS build process, and thus has easy access to it when building Perl, but ordinary users would need to go to a great deal of effort to obtain the information needed for pre-binding.

You can override the default and build a shared libperl if you wish (Configure ... -Duseshrplib).

With Mac OS X 10.4 "Tiger" and newer, there is almost no performance penalty for non-prebound libraries. Earlier releases will suffer a greater load time than either the static library, or Apple's pre-bound dynamic library.

Updating Apple's Perl

In a word - don't, at least not without a *very* good reason. Your scripts can just as easily begin with "#!/usr/local/bin/perl" as with "#!/usr/bin/perl". Scripts supplied by Apple and other third parties as part of installation packages and such have generally only been tested with the /usr/bin/perl that's installed by Apple.

If you find that you do need to update the system Perl, one issue worth keeping in mind is the question of static vs. dynamic libraries. If you upgrade using the default static libperl, you will find that the dynamic libperl supplied by Apple will not be deleted. If both libraries are present when an application that links against libperl is built, ld will link against the dynamic library by default. So, if you need to replace Apple's dynamic libperl with a static libperl, you need to be sure to delete the older dynamic library after you've installed the update.

Known problems

If you have installed extra libraries such as GDBM through Fink (in other words, you have libraries under /sw/lib), or libdlcompat to /usr/local/lib, you may need to be extra careful when running Configure to not to confuse Configure and Perl about which libraries to use. Being confused will show up for example as "dyld" errors about symbol problems, for example during "make test". The safest bet is to run Configure as

    Configure ... -Uloclibpth -Dlibpth=/usr/lib

to make Configure look only into the system libraries. If you have some extra library directories that you really want to use (such as newer Berkeley DB libraries in pre-Panther systems), add those to the libpth:

    Configure ... -Uloclibpth -Dlibpth='/usr/lib /opt/lib'

The default of building Perl statically may cause problems with complex applications like Tk: in that case consider building shared Perl

    Configure ... -Duseshrplib

but remember that there's a startup cost to pay in that case (see above "libperl and Prebinding").

Starting with Tiger (Mac OS X 10.4), Apple shipped broken locale files for the eu_ES locale (Basque-Spain). In previous releases of Perl, this resulted in failures in the lib/locale test. These failures have been suppressed in the current release of Perl by making the test ignore the broken locale. If you need to use the eu_ES locale, you should contact Apple support.

Cocoa

There are two ways to use Cocoa from Perl. Apple's PerlObjCBridge module, included with Mac OS X, can be used by standalone scripts to access Foundation (i.e. non-GUI) classes and objects.

An alternative is CamelBones, a framework that allows access to both Foundation and AppKit classes and objects, so that full GUI applications can be built in Perl. CamelBones can be found on SourceForge, at <https://www.sourceforge.net/projects/camelbones/>.