That means you cannot use quantifiers (?, *, +, or ) or alternation of different-length items inside them. Look-behind expressions cannot be of variable length. The directional indicator ( <) is only present in the look-behind and comes before the positive or negative indicator. characterĮvery extended pattern is written as a parenthetical group with a question mark as the first character. Zero-length assertions can also be used to match extended patterns and require that a pattern match succeed ( positive assertion) or fail ( negative assertion). Match at the end of a string (or line if /m is used) Match at the beginning of a string (or line if /m is used) characterĪlso known as zero-width (length) assertions, these do not match any characters but "look around" to see what comes before and/or after the current position. These can be used on their own or within a character class. Unless first, last, or escaped (i.e., : match a, d, or -), used for a range ( : match any character in the range from a to b) If the first character of a class, negates that class Resets the beginning of the match to the current position (this only affects what is reported as the full match) Specifies a range of occurrences for the element preceding itĭefine character class, matches any one of the characters contained within the bracketsĮscapes next character, i.e., modify the meaning of the next character Groups subexpressions without capturing (cluster) Groups subexpressions for capturing to $1, $2. Matches either the subexpression preceding or following it ![]() Match any single character (except \n use /s to match \n, too) The following characters need to be escaped because they have special meanings: Match at least n times but no more than m times Match (or lazy match) 0 or 1 times, i.e., at most once Match 1 or more times, i.e., at least once Match 0 or more times, i.e., any number of times In order to match as few characters as possible, follow them with a ?. By default, they are "greedy" meaning they attempt to match as many characters as possible. These quantifiers apply to the preceding atom. ![]()
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