替換第幾個匹配

pp=/java/java/java/java/java/java/jdk.1.7

#orign token replacement index
replaceByIdx(){
	p=$1
	for(( i = 1;i<=$4;++i )); do
		p=$(echo $p | sed 's:'$2':'$3':')
	done;

	for(( i=1;i<=$(expr $4 - 1);++i)); do
		p=$(echo $p | sed 's:'$3':'$2':')
	done;
	echo $p
}
re=$(replaceByIdx $pp java pppp 4)
echo $re