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Regex Difference: (\W+)? and (\W*)

Alexander Ross • • 2 min read
Regex Difference: (\W+)? and (\W*)

Is there any difference between (\w+)? and (\w*) in regex?

It seems the same, doesn't it?

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1 Answer

(\w+)? and (\w*) both match the same (0..+inf word characters)

However, there is a slight difference:

In the first case, if this part of the regex matches "", the capturing group is absent. In the second case, it is empty. In some languages, the former manifests as a null while the latter should always be "".

In Javascript, for example, 

/(\w*)/.exec("")  // ["", ""]
/(\w+)?/.exec("") // ["", undefined]

In PHP (preg_match), in the former case, the corresponding key is simply absent in the matches array:

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Alexander Ross
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Alexander Ross

Alexander Ross has covered the video game industry for a decade, writing deep dives on game design, esports tournaments, VR developments, and gaming culture.