Matching an empty string with regex

Question

I\'ve seen posts here on stackoverflow that say that the regex ^$ will match an empty string... So it made me think... why not something like this: ^\\s+$

Answer 1

^\s+$ - does that not also work?

Not for matching an empty string. In general, X+ means X one or more times. So, \s+ cannot match the empty string - it requires at least one \s in order to match.

                                     ^ \s + $
                                     | |  | |
start of string ---------------------+ |  | |
whitespace character ------------------+  | |
one or more of what precedes -------------+ |
end of string ------------------------------+

Now, X* means X 0 or more times, so ^\s*$ would indeed match an empty string.

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^\s+$

^\s*$