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13.2.1 Basic assertions
The assertions ^
and $
identify the beginning and
the end of the text string respectively. They ensure that their
adjoining regexps match at one or other end of the text string.
Examples:
(pregexp-match-positions "^contact" "first contact") ⇒ #f
The regexp fails to match because contact
does not
occur at the beginning of the text string.
(pregexp-match-positions "laugh$" "laugh laugh laugh laugh") ⇒ ((18 . 23))
The regexp matches the last laugh
.
The metasequence \b
asserts that
a word boundary exists.
(pregexp-match-positions "yack\\b" "yackety yack") ⇒ ((8 . 12))
The yack
in yackety
doesn’t end at a word
boundary so it isn’t matched. The second yack
does and is.
The metasequence \B
has the opposite effect to \b
. It
asserts that a word boundary does not exist.
(pregexp-match-positions "an\\B" "an analysis") ⇒ ((3 . 5))
The an
that doesn’t end in a word boundary
is matched.
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