Regex to remove repeated character pattern in a string

Question

I have a string that may have a repeated character pattern, e.g.

\'xyzzyxxyzzyxxyzzyx\'

I need to write a regex that would replace such str

Answer 1

Try this regex pattern and capture the first group:

^(.+?)\1+$

• ^ anchor for beginning of string/line
• . any character except newlines
• + quantifier to denote atleast 1 occurence
• ? makes the + lazy instead of greedy, hence giving you the shortest pattern
• () capturing group
• \1+ backreference with quantifier to denote that pattern should repeat atleast once
• $ anchor for end of string/line

Test it here: Rubular

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The above solution does a lot of backtracking affecting performance. If you know the which characters are not allowed in these strings, then you can use a negated characted set which eliminates backtracking. For e.g., if whitespaces are not allowed, then

^([^\s]+)\1+$