K.7.2 Regexp Replacement

The M-x replace-string command replaces exact matches for a single string. The similar command M-x replace-regexp replaces any match for a specified pattern.

In replace-regexp, the newstring need not be constant: it can refer to all or part of what is matched by the regexp. `\&' in newstring stands for the entire match being replaced. `\d' in newstring, where d is a digit, stands for whatever matched the dth parenthesized grouping in regexp. To include a `\' in the text to replace with, you must enter `\\'. For example,

M-x replace-regexp RET c[ad]+r RET \&-safe RET

replaces (for example) `cadr' with `cadr-safe' and `cddr' with `cddr-safe'.

M-x replace-regexp RET \(c[ad]+r\)-safe RET \1 RET

performs the inverse transformation.