remember, the forward slash is not a metacharacter, so it doesn't need to be backslashed when it's not the delimiter 斜干/不是特殊的符号,他没必要在前面加反斜干(\),当他不是定界符的时候
to do this, we surround those " interesting parts " with backslashed parentheses, so that we can refer to them in our replacement string using-1,-2-, and-3 to tell sed where to insert them 要这样做,我们用带有反斜杠的圆括号括起那些“感兴趣部分”,以便可以在替换字符串中引用它们(使用\1、\2\和\3来告诉sed将它们插入到何处)。