模式匹配

1. 括号的分组标签，最多9组，依次为1...9

sed -r 's/^(address)/#1/' /etc/network/interfaces
sed -r s/^(address)/#\1/ /etc/network/interfaces

2. 用&代表匹配到的内容

sed -r 's/^address/#&/' /etc/network/interfaces