use English qw/-no_match_vars/;
...
our $filespec;
if ($OSNAME =~ /win/i) {
    $filespec =
        qr{ (\A(?:[[:alpha:]]:)?[ \\ \. \- [:space:] [:word:] ]+)\z }msx;
}
else {
    $filespec = qr{ (\A[- + @ [:word:] . / ]+)\z }msx;
}
...
our $perl = untaint_path( $EXECUTABLE_NAME, '$perl' );
...

sub untaint_path {
    my ( $path, $description ) = @_;

    if ( !( $path =~ $filespec ) ) {
         die "$description is tainted.\n";
    }

    return $1;
}