DB<138> sub Basename {
           my ($file) = $0 =~ m#/?([^/]+)$#;
           return $file;
           }

  DB<139> $0="a/b"
 => "a/b"

  DB<140> $a=Basename()
 => "b"

  DB<141> $0="b"
 => "b"

  DB<142> $a=Basename()
 => "b"