Vim Search and Replacing with Backreferences

It is often helpful to write search and replace commands that save segments of the matched text to use in the replacement string.

Source text:

This is some text (we want to change) with a phone number (301) 555-1234.
We want to remove the parenthesis, but only from the phone number string.

In this example we have a text file that has a phone number in it and we want to remove the parenthesis that surround ONLY the area code in the phone number, plus the trailing space and replace it with the aread code plus a trailing “-“.

Following is the search and replace command. The forward slashes are separators in the search command.  They will be omitted in the full explanation below:

:1,%s/(\([0-9]\+\))\s/\1-/g

Here is it explained:

:1,%s

Tells, vi to execute the search and replace command from line 1 to the end of the document

(\([0-9]\+\))\s

The regex including the backreference that will find the area code including the parenthesis and a trailing space.  The \(  and \) parenthesis wrap the numerical part of the string that we are trying to save and mark it as a backreference.  The \+ indicates that we one one or more of the numerical characters (the plus char must be escaped).  The \s indicates a whitespace character the we also want to match.

\1-

The characters that we want to use to replace what we have found.  The \1 indicates we want to use the first backreference that was matched followed by a ‘-‘ character. 

g

Tells, vi to execute the search and replace on all occurances found in a line.