Suppose there is a function that generates one file based on another:

    sub compile($$)
    {
        my ($source_filename, $output_filename) = @_;

        ... # compile source into output
    }
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and now we only want to execute the function if $source_filename has been modified more recently than $output_filename...

    sub compare_modification_times($$)
    {
        my ($file_a, $file_b) = @_;

        ???

    }

    my $src = "wee.foo";
    my $dest = "wee.bar";

    if (compare_modification_times($src, $dest) < 0)
    {
        compile($src, $dest);
    }
[download]

I would like recommendations on the most robust and portable way to implement compare_modification_times. Any ideas?

Thanks for your time.