These functions operate on regular expressions.
This function returns a regular expression whose only exact match is
string. Using this regular expression in
succeed only if the next characters in the buffer are string;
using it in a search function will succeed if the text being searched
contains string. See Regexp Search.
This allows you to request an exact string match or search when calling a function that wants a regular expression.
(regexp-quote "^The cat$") ⇒ "\\^The cat\\$"
One use of
regexp-quote is to combine an exact string match with
context described as a regular expression. For example, this searches
for the string that is the value of string, surrounded by
(re-search-forward (concat "\\s-" (regexp-quote string) "\\s-"))
The returned string may be string itself if it does not contain any special characters.
This function returns an efficient regular expression that will match any of the strings in the list strings. This is useful when you need to make matching or searching as fast as possible—for example, for Font Lock mode20.
If strings is the empty list, the return value is a regexp that never matches anything.
The optional argument paren can be any of the following:
The resulting regexp is preceded by paren and followed by ‘\)’, e.g. use ‘"\\(?1:"’ to produce an explicitly numbered group.
The resulting regexp is surrounded by ‘\<\(’ and ‘\)\>’.
The resulting regexp is surrounded by ‘\_<\(’ and ‘\)\_>’ (this is often appropriate when matching programming-language keywords and the like).
The resulting regexp is surrounded by ‘\(’ and ‘\)’.
The resulting regexp is surrounded by ‘\(?:’ and ‘\)’, if it is necessary to ensure that a postfix operator appended to it will apply to the whole expression.
The returned regexp is ordered in such a way that it will always match the longest string possible.
Up to reordering, the resulting regexp of
equivalent to but usually more efficient than that of a simplified
(defun simplified-regexp-opt (strings &optional paren) (let ((parens (cond ((stringp paren) (cons paren "\\)")) ((eq paren 'words) '("\\<\\(" . "\\)\\>")) ((eq paren 'symbols) '("\\_<\\(" . "\\)\\_>")) ((null paren) '("\\(?:" . "\\)")) (t '("\\(" . "\\)"))))) (concat (car parens) (mapconcat 'regexp-quote strings "\\|") (cdr parens))))
This function returns the total number of grouping constructs (parenthesized expressions) in regexp. This does not include shy groups (see Regexp Backslash).
This function returns a regular expression matching a character in the list of characters chars.
(regexp-opt-charset '(?a ?b ?c ?d ?e)) ⇒ "[a-e]"
This variable contains a regexp that is guaranteed not to match any string at all. It is particularly useful as default value for variables that may be set to a pattern that actually matches something.
regexp-opt does not
guarantee that its result is absolutely the most efficient form
possible. A hand-tuned regular expression can sometimes be slightly
more efficient, but is almost never worth the effort.