use Cwd;

  print cwd(), "\n";

  -e 'foo' or mkdir('foo', 0777) or die "Can't mkdir 'foo': $!\n";

  open(FH, '>foo/bar') or warn "Can't open 'foo/bar': $!\n";
    # creates a file named 'foo/bar' in cwd

  open(FH, '>foo:bar') or warn "Can't open 'foo:bar': $!\n";
    # fails, unless you actually have a volume named 'foo'
    # in that case, creates a file named 'bar' on the volume 'foo'

  open(FH, '>:foo:bar') or warn "Can't open ':foo:bar': $!\n";
    # creates a file named 'bar' in the directory 'foo' in the cwd