Zero-Width Assertions(零宽度断言) 这种结构产生的匹配结果长度为0(所以称作零宽度),只是用于对上下文环境做判断(所以称作断言)。 ^ 如果使用Multiline选项,匹配每一行的开始位置;如果使用Singleline选项,匹配整个字符串开始位置。^如果出现在[]中就不是Zero-Width Assertion了。 $ 如果使用Multiline选
characters—that is, characters will not be returned in a result. They are also known as zero-width assertions. A zero-width assertion doesn’t match a character, per se, but rather a location in a string. Some of these, such as ^ and $, are also called anchors. 单词边界:\b 有些...
(?(expression)yes|no) Matches yes if expression matches; otherwise, matches the optional no part. expression is interpreted as a zero-width assertion. (?(A)A\d{2}\b|\b\d{3}\b) "A10", "910" in "A10 C103 910" (?(name)yes|no) Matches yes if the named capture name has a mat...
In regex speak, a word boundary (\b) is a "zero width assertion", meaning that it doesn't represent a http://perldoc.perl.org Page 12 Perl version 5.12.4 documentation - perlfaq6 character in the string, but a condition at a certain position. For the regular expression, /\bPerl\b...
A negative character group in a larger regular expression pattern is not a zero-width assertion. That is, after evaluating the negative character group, the regular expression engine advances one character in the input string. Some common regular expression patterns that contain negative character grou...
Substitutions are regular expression language elements that are supported in replacement patterns. For more information, seeSubstitutions. The metacharacters listed in the following table are atomic zero-width assertions. Back to top Miscellaneous Constructs ...
Zero-width assertions do not advance the position counter in the input string. They either look ahead of or immediately behind the current position to determine whether the pattern defined by the assertion is true. If it is not, the match fails. (For information...
A negative character group in a larger regular expression pattern is not a zero-width assertion. That is, after evaluating the negative character group, the regular expression engine advances one character in the input string.Some common regular expression patterns that contain negative character groups...
(?=...) Zero-width positive lookahead assertion (?*pla:...) Same; avail experimentally starting in 5.28 (?!...) Zero-width negative lookahead assertion (?*nla:...) Same; avail experimentally starting in 5.28 (?<=...) Zero-width positive lookbehind assertion ...
The \G assertion is true only when the current matching position is at the start point of the matching process, as specified by the startoffset argument of pcre2_match(). It differs from \A when the value of startoffset is non-zero. By calling pcre2_match() multiple times with appropriat...