debian-bash/tools/append_or_replace

#!/bin/bash


usage() {
	echo "Usage: $(basename "$0") <REGEX> <STRING> <FILE>"
}

if [[ $# -ne 3 ]]; then
	usage
	exit 2
fi 

REGEX=$1
STRING=$2
FILE=$3

grep -q "$REGEX" $FILE
if [ $? -eq 1 ]; then
    echo "$STRING" >> $FILE
	echo appended
else
    sed -i "s/$REGEX/$STRING/g" $FILE
	echo replaced
fi