# setup
cd /var/tmp/
touch foo
f='../../var/tmp/foo'

# for just the directory:
d=`(cd ${f%/*} && pwd)`
#or:
d=`dirname $f`
d=`cd $d && pwd`

# for the filename (rel2abs):
d=`dirname $f`
d=`cd $d && pwd`
f=`basename $f`
f=`/bin/ls $d/$f`