12.4 Regular Expression Search
A "regular expression" ("regexp", for short) is a pattern that denotes
a (possibly infinite) set of strings. Searching for matches for a
regexp is a powerful operation that editors on Unix systems have
To gain a thorough understanding of regular expressions and how to
use them to best advantage, we recommend that you study `Mastering
Regular Expressions, by Jeffrey E.F. Friedl, O'Reilly and Associates,
1997'. (It's known as the "Hip Owls" book, because of the picture on its
cover.) You might also read the manuals to Note: (gawk)Top, Note:
(ed)Top, `sed', `grep', Note: (perl)Top, Note: (regex)Top, Note:
(rx)Top, `pcre', and Note: (flex)Top, which also make good use of
The XEmacs regular expression syntax most closely resembles that of
`ed', or `grep', the GNU versions of which all utilize the GNU `regex'
library. XEmacs' version of `regex' has recently been extended with
some Perl-like capabilities, described in the next section.
In XEmacs, you can search for the next match for a regexp either
incrementally or not.
Incremental search for a regexp is done by typing `M-C-s'
(`isearch-forward-regexp'). This command reads a search string
incrementally just like `C-s', but it treats the search string as a
regexp rather than looking for an exact match against the text in the
buffer. Each time you add text to the search string, you make the
regexp longer, and the new regexp is searched for. A reverse regexp
search command `isearch-backward-regexp' also exists, bound to `M-C-r'.
All of the control characters that do special things within an
ordinary incremental search have the same functionality in incremental
regexp search. Typing `C-s' or `C-r' immediately after starting a
search retrieves the last incremental search regexp used: incremental
regexp and non-regexp searches have independent defaults.
Non-incremental search for a regexp is done by the functions
`re-search-forward' and `re-search-backward'. You can invoke them with
`M-x' or bind them to keys. You can also call `re-search-forward' by
way of incremental regexp search with `M-C-s <RET>'; similarly for
`re-search-backward' with `M-C-r <RET>'.
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