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I want to match patterns of alternating lowercase characters.
ababababa -> match
I tried this
([a-z][a-z])+[a-z]
but this would be a match too
ababxyaba
452
$ 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.
[] denotes a character class. () denotes a capturing group. [a-z0-9] -- One character that is in the range of a-z OR 0-9. (a-z0-9) -- Explicit capture of a-z0-9 .
Using special characters For example, to match a single "a" followed by zero or more "b" s followed by "c" , you'd use the pattern /ab*c/ : the * after "b" means "0 or more occurrences of the preceding item."
Regular expression pattern-matching can be performed with either a single character or a pattern of one or more characters in parentheses, called a character pattern. Metacharacters have special meanings, as described in the following table.
You can use this regex with 2 back-reference to match alternating lowercase letters:
^([a-z])(?!\1)([a-z])(?:\1\2)*\1?$
RegEx Demo
RegEx Breakup:
^: Start([a-z]): Match first letter in capturing group #1(?!\1): Lookahead to make sure we don't match same letter again([a-z]): Match second letter in capturing group #3(?:\1\2)*: Match zero or more pairs of first and second letter\1?: Match optional first letter before end$: End
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