consider the following situation: $ myscript filename if the user enter more than one filename, eg: $ myscript filename filename1 , then echo "error" else, if the user enter no filename, eg: $ myscript , then the user is given one more chance to enter the filename again, if the second time the user enter no filename again, then the myscript will exit, but if the user enter more than one filename for the second time, then the echo "error" mentioned before will be displayed.

Here is that logic using a case statement: #!/bin/sh case $# in 1) filename=$1;; 0) echo "Please enter filename: \c" read filename morestuff if [ -z "$filename" ] ; then exit fi if [ -n "$morestuff" ] ; then echo error exit 1 fi;; *) echo error exit 1;; esac echo "Will now process $filename ..." exit 0 And without using a case statement ... #!/bin/sh if [ $# -gt 1 ] ; then echo error exit 1 fi if [ $# -eq 1 ] ; then filename=$1 else echo "Please enter filename: \c" read filename morestuff if [ -z "$filename" ] ; then exit fi if [ -n "$morestuff" ] ; then echo error exit 1 fi fi echo "Will now process $filename ..." exit 0

I considered the situation. What's the question?