Regex Cheat Sheet

Both are quantifiers applied to the item before them. The asterisk means "zero or more", so it can match nothing at all, while the plus means "one or more" and requires at least one occurrence. That is why /ab*c/ matches "ac" but /ab+c/ does not.

\b matches a word boundary — the zero-width position between a word character (a letter, digit, or underscore) and anything else, including the start or end of the string. It consumes no characters, which is why /\bcat\b/ matches "cat" in "the cat sat" but not inside "concatenate".

A greedy quantifier such as .* takes as much text as it can and then gives characters back until the rest of the pattern fits. A lazy quantifier, written by adding a question mark as in .*?, takes as little as possible and expands only when it has to. Greedy matching is the default and is the usual cause of a pattern matching far more text than intended.

Put a backslash in front of it. The characters that need escaping outside a character class are . ? * + ( ) [ ] { } | ^ $ / and the backslash itself. Inside a character class most of these are already literal — only ^ (at the start), ] , - , and \ need care.

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