[FIXED] How can I check if a binary dependency is available in Perl?

Issue

Having volunteered to maintain a stagnant CPAN package (GnuPG) I'd like improve the install files such that they exit gracefully if the gpg binary (which GnuPG is a wrapper for) cannot be found. After a bit of seeking inspiration from other packages, I've come up with adding this to Makefile.PL:

my @paths = grep { -x "$_/gpg" } split /:/, $ENV{PATH}, $ENV{PGP_PATH};

unless ( scalar @paths ) {
    print <<EOD;
I can't find the gpg binary on your system. If it's not installed in your usual PATH, set $ENV{PGP_PATH} to include where it can be found and try installing again.
EOD

    exit(0);
}

WriteMakefile(
    'NAME'        => 'GnuPG',
    'VERSION_FROM' => 'GnuPG.pm',
    'EXE_FILES'    => [ gpgmailtunl ],
    'LICENSE'      => 'GPL',
    'LIBS'         => [ @paths ],
);

Does that look sane?

Solution

The general concept is fine - if what you need to work is not present, don't create the makefile. The CPAN Testers have rules about exiting with a zero status on failure (which annoys me a lot, but never mind; I hate failing with a success status!).

Question: do you keep a record of where PGP was found at install time, so that if somebody else uses the Perl module without the location on their path, the module can still run?

For DBD::Informix, I have rigid dependencies without which the module cannot be compiled; the Makefile.PL is a major production in its own right because of that. It also tries to handle versions of the software covering over 15 years; that complicates its life, too. If the pre-requisites (some Perl modules; some non-Perl software) is not available, it won't install.

Answered By - Jonathan Leffler

Answer Checked By - David Marino (PHPFixing Volunteer)