#!/bin/sh

echo $1
case "$1" in
"")
                echo "must enter one argument";
                exit 0
            ;;
esac
DIR=$2
case "$2" in
"")
	echo "must enter 2 nd  argument";
	exit 0
DIR=.
	;;
esac

cat "$1" | sed -e "s/$2/$3/g" > /tmp/tmpfile && cat /tmp/tmpfile > "$1";