Using different Regex operations

Example of Regex operations * All examples below are having a pattern, matched strings in green and unmatched in red. Concatenation Simplest ; Concatenating a bunch of symbols together aabaab  aabaab  every other string  Logical OR (Alternation) To choose from one of several possibilities aa | baab  aa baab  every other string  Replication To specify infinitely many possibilities ; Note : 0 replications of b are permitted. ab*a  aa aba  abba  ab ababa Grouping To specify precedence to the various operators  The replication operator has the highest precedence, then concatenation, then logical OR. a(a|b)aab  aaaab abaab  every other string Wildcard It matches exactly one occurrence of any single character. a..a  abba abaa  aa aaaaa  One or more a(bc)+de  abcde abcbcde  ade abc Once or Not at all a(bc)?de  ade abcde abc abcbcde Character classes (Range) [a-m]*  blackmail imbecile  above below Negation of character classes (Range) [^aeiou]  b c  a e Exactly N times [^aeiou]{6}  rhythm syzygy  rhythms allowed Between M and N times [a-z]{4,6}  spider tiger  jellyfish cow Whitespace characters [a-z\s]*hello  hello say hello  Othello 2hello