12.7.2 Regexp Replacement

replace-string replaces exact matches for a single string. The similar command 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 text being replaced. ‘\d’ in newstring, where d is a digit, stands for whatever matched the d’th parenthesized grouping in regexp. For example,

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

would replace (for example) ‘cadr’ with ‘cadr-safe’ and ‘cddr’ with ‘cddr-safe’.

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

would perform exactly the opposite replacements. To include a ‘\’ in the text to replace with, you must give ‘\\’.