Implement dirname as a bash function. Make sure it behaves sensibly when given such arguments as /.

Question

The dirname utility treats its argument as a pathname and writes to standard out-
put the path prefix—that is, everything up to but not including the last component:
$ dirname a/b/c/d
a/b/c
If you give dirname a simple filename (no / characters) as an argument,
dirname writes a . to standard output:
$ dirname simple

Answer 1

$ function dn () {
> if [ $# = 0 ]
> then
> exit 1
> elif [ "$1" = "/" ]
> then
> echo /
> elif (echo "$1" | grep -v "/" > /dev/null 2>&1)
> then
> echo .
> else
> echo $1 | sed 's:\(.*\)/.*:\1:'
> fi
> }