Online regex

A regular expression (shortened as regex or regexp; also referred to as rational expression) is a sequence of characters that specifies a search pattern in text . Usually such patterns are used by string-searching algorithms for “find” or “find and replace” operations on strings, or for input validation.

$ means “Match the end of the string ” (the position after the last character in the string). Both are called anchors and ensure that the entire string is matched instead of just a substring.

\d (digit) matches any single digit (same as [0-9] ). The uppercase counterpart \D (non-digit) matches any single character that is not a digit (same as [^0-9] ).