What strings does this regex matches? (a|b) | Hacker News Reader

What strings does this regex matches? (a|b)

regepxal is showing infinite matches and shows "baaaaaaa" as a match. Doesn't (a|b) means a or b? * means match 0 or more times. So, it should be matching aa,aaa,bb,bbb, , etc? I'm not getting how baaaa is a match. Can anyone clarify please?

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You want:

  (a*)|(b*)

The strings of at most 3 that this matches are:

  e, a, aa, aaa, b, bb, bbb

It appears that you have:

  (a|b)*

The strings of at most 3 that this matches are:

  e, a, b, aa, ab, ba, bb, aaa, aab, aba, abb, baa, bab, bba, bbb

Where e is the empty string

Each repetition can take a different path through the repeated expression. You don’t choose a value for the inner expression once and then repeat it; rather, each time you repeat you can select a value anew for the inner expression.

PS: This question would be more appropriate on stackoverflow.

/(a|b)/ does mean roughly "a string with an 'a' or a 'b' in it". So /(a|b)/ should have "baaaaaa" as a match. The string has an 'a'. The string has a 'b'. It matches.

its (a|b)*

OP Updates:

I feel I'm not getting it. I feel I'm missing something that you have good grasp of. You choose a or b and repeat, so aaaa, bbbb should be only matches. Could you help me out?

(b)(aaa...)

Each char can be an a or b, then repeat, not "a repeating seq of either a or b only"

(a|b)* = X* = x1x2x3... where each xi can be "a" or "b"

this cleared my confusion. Thank you

OP updates:

Thank you. The perfect way to think about this for me is this:

(X)*= X X X X X X

Here X=a or b

So,

a or b then a or b then a or b then....

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