dirname_basename_string_substitute_bash

Reference: http://tldp.org/LDP/LG/issue18/bash.html

Given:
foo=/tmp/my.dir/filename.tar.gz
We can use these expressions:
path = ${foo%/*}
To get: /tmp/my.dir (like dirname)
file = ${foo##*/}
To get: filename.tar.gz (like basename)
base = ${file%%.*}
To get: filename
ext = ${file#*.}
To get: tar.gz
Note that the last two depend on the assignment made in the second one

if you want to get 
/one/two/three/four.blah 
and turn it into 
/one/two
you can
i=/one/two/three/four.blah
echo ${i%/*/*}
/one/two