file_name_is_absolute
Takes as its argument a path, and returns true if it is an absolute path.
    $is_absolute = File::Spec->file_name_is_absolute( $path );
This does not consult the local filesystem on Unix, Win32, OS/2, or Mac OS (Classic). It does consult the working environment for VMS (see file_name_is_absolute in File::Spec::VMS).