Search and replace part of an expression in gvim

Assume that you want to add a double asterisk (**) to every line in a document.

e.g. you want to replace
hello, this is a line
this is another line
this is a third line

with
hello, this is a line**
this is another line**
this is a third line**


There are many ways to doing this, but one of the more general ways of doing this with regular expressions (which can be easily extended for other tasks) is

:%s/\(^.*\)/\1**

An extension: What if you want to introduce a line break before the word line?

Use \r

:%s/\(^.*\) \(line\*\*\)/\1\r\2/g should do it for you


As you notice \1 contains the match within the first parentheses. If there were multiple parentheses, the contents can be accessed using \1, \2 etc.