Implement the basename utility, which writes the last component of its pathname argument to standard output, as a bash function. For example, given the pathname a/b/c/d, basename writes d to standard output:

$ basename a/b/c/d
d

The following function is named bn to distinguish it from the basename util-
ity. It behaves the same way as basename.

$ function bn () {
> if [ $# = 0 ]; then
> exit 1
> elif [ "$1" = "/" ]
> then
> echo /
> else
> echo $1 | sed 's:.*/::'
> fi
> }