20.7 Regular Expression Example
Here is a complicated regexp—a simplified version of the regexp
that Emacs uses, by default, to recognize the end of a sentence
together with any whitespace that follows. We show its Lisp syntax to
distinguish the spaces from the tab characters. In Lisp syntax, the
string constant begins and ends with a double-quote. ‘\"’ stands
for a double-quote as part of the regexp, ‘\\’ for a backslash as
part of the regexp, ‘\t’ for a tab, and ‘\n’ for a newline.
"[.?!]\"')]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
This contains four parts in succession: a character set matching
period, ‘?’, or ‘!’; a character set matching
close-brackets, quotes, or parentheses, repeated zero or more times; a
set of alternatives within backslash-parentheses that matches either
end-of-line, a space at the end of a line, a tab, or two spaces; and a
character set matching whitespace characters, repeated any number of
To enter the same regexp in incremental search, you would type
<TAB> to enter a tab, and C-j to enter a newline. You would
also type single backslashes as themselves, instead of doubling them
for Lisp syntax. In commands that use ordinary minibuffer input to
read a regexp, you would quote the C-j by preceding it with a
C-q to prevent C-j from exiting the minibuffer.