What is the alternation operator in Lua patterns?

Question

In regex, | is used for alternation. What is the corresponding character in Lua patterns?

Phytogeography

See also Lua string.match uses irregular regular expressions? – Scrivner

Answer 1

First, note that Lua patterns are not regular expressions; they are their own simpler matching language (with different benefits and drawbacks).

Per the specification I've linked to above, and per this answer, there is no alternation operator in a Lua pattern. To get this functionality you'll need to use a more powerful Lua construct (like LPEG or a Lua Regex Library).

Scrivner

I will complement this perfectly good answer by saying that sometimes you can get away with not using LPEG or Lua Regex - a plain ´or´ might do the trick: if s:match(a) or s:match(b) then ... – Hawserlaid

often you can also get away with a more general match and switch on the result...: local word = s:match("%w+") if word =="foo" or word == "bar" then.... else ....... end – Kaela

I came to this question from the perspective of Arduino Regexp (which is based on Lua patterns). I was hoping this answer would include a work-around that I could port. – Adi

Answer 2

Lua does not have alternations in patterns you cannot use (test1|test2). You can only choose between multiple characters like [abcd] will match a, b, c or d.

Karat

Answer 3

Another workaround is: Instead of:

apple|orange

Write:

[ao][pr][pa][ln][eg]

Explanation: match alternate letters from each word. voila!

Heterochromous

That would match arplg as well. – Sailing