Yesterday at work, a customer spotted a typo in our UI: “you can use the use the Tailscale CLI”. After the typo was fixed, I wanted to find other cases of accidentally repeated words or phrases. I used two regular expressions to search every codebase for unnecessary repetition.

The first regex finds repeated words:

\b([A-Za-z]+) \1\b

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There’s a capturing group for a single word made up of letters ([A-Za-z]+), a space, then a backreference to the group. I used [A-Za-z] rather than the word metacharacter \w because I didn’t want to include numbers, which would dramatically increase the number of matches in a codebase. This skips repetitions which include accented characters, but that’s fine because those are rare in my writing.

That expression is surrounded by word boundary assertions \b, which check that I’m at the start/end of a word – this avoids finding repeated character sequences within longer words, like “with the reason”.

The second regex finds repeated phrases:

\b([A-Za-z]+ [A-Za-z]+) \1\b

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I’ve changed the capturing group, so now it looks for two words separated by a space.

Sometimes repetition is useful, like when I really really want to emphasise a point, but often it’s just a typo. Cleaning up these mistakes has been a fun Friday cleanup task.