Thx for spotting the same problem! ;)

Here another version¹ independent from callers context!

  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"
[download]

¹) Just for didactic reasons, using a well tested basename-sub from CPAN is almost always better, File::Basename is even core!

  DB<153> use File::Basename

  DB<159> basename("a")
 => "a"

  DB<160> basename("a/b")
 => "b"

  DB<161> basename("a/b/c")
 => "c"

  DB<162> basename("a/")
 => "a"
[download]