if [ $# -lt "3" ] 
then 
	echo Usage: gres pattern replacement file
	exit
fi
pattern=$1
replacement=$2
if [ -f $3 ] 
then 
	file=$3
else
	echo $3 is not a file.
	exit
fi
sed -e 's/'$pattern'/'$replacement'/' $file
#
#This shell script is a front end for sed.