However, if we add a lazy identifier ? behind the zero-or-more quantifier, it makes the quantifier lazy, causing it to match as few characters as possible. Notice how it skips over three b characters and only stops the match right at the last b. This will produce the following matches: a nother baby bathtub This is because the zero-or-more quantifier * is greedy. The following expression will match as many characters between a and b as it can. * (?=b ) /g Match All Characters Greedy vs. * (?=b ) /įinally, to return every instance of this match and not just the first, we include the global modifier g at the very end of the expression: / ( ?<=a ). In this case, we use the character b inside the positive look-ahead: / ( ?<=a ). This will ensure that the matched string is directly followed by whatever is in the place of …. This is specified by a positive look-ahead (?=… ). We want to stop matching when we encounter a b character. On its own, the dot symbol will only match a single character, so we need to include a zero-or-more quantifier * behind it to ensure that we match zero or more of any character. which will match any character except a newline character. Their contents ( a in this case) are not matched.Īfter the presence of the a character, we want to match any character. Look-aheads and look-behinds are assertive, which means that they are only used to check if a certain condition is true. In this case, we want to ensure that the letter a directly precedes the matched string. The expression starts with a positive look-behind ( ?<=… ) which ensures that the matched string is preceded to whatever is in the place of …. to select all contents between the delimiters.Īn expression that does matches everything between a and b is: / ( ?<=a ). C:/documents/work/).Ī regular expression that matches all characters between two specified characters makes use of look-ahead (?=… ) and look-behind ( ?<=… ) statements to isolate the string, and then uses the dot character. This can be useful for things like extracting contents of parentheses like (abc) or for extracting folder names from a file path (e.g. Regex can be used to select everything between the specified characters.
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