capture word a or b and part of optional extra arguments

Question

First of all this doesn't match ok or capture "ok".find("(ok|capture)") -- nil

Second, followed by ok match an optional ok;args but only capture args as parameter. This is wrong "ok;args".find("(ok)(;.+)?"), and capture group includes extra ;.

function mymatch(str)
  local _, _, ok, oreveal = str:find("(ok)")
  return ok, oreveal
end

-- this is what I want
print(mymatch("ok")) -- ok nil
print(mymatch("cancel")) -- cancel nil
print(mymatch("ok;domatch")) -- ok domatch
print(mymatch("okdontmatch")) -- nil nil

Answer 1

You can use

function mymatch(str)
  local _, _, ok, oreveal = str:find("^(ok%f[%A]);?(.*)$")
  if ok == nil then
    _, _, ok, oreveal = str:find("^(cancel%f[%A]);?(.*)$")
  end
  if oreveal == "" then
    oreveal = nil
  end
  return ok, oreveal
end

-- this is what I get
print(mymatch("ok")) -- ok nil
print(mymatch("cancel")) -- cancel nil
print(mymatch("ok;domatch")) -- ok domatch
print(mymatch("okdontmatch")) -- nil nil

See the online Lua demo.

The ^(ok%f[%A]);?(.*)$ pattern matches

• ^ - start of string
• (ok%f[%A]) - Group 1: ok and a trailing "word boundary" (%f[%A] is a frontier pattern making sure that the next char if present must be a non-letter)
• ;? - an optional ;
• (.*) - Group 2: the rest of the string
• $ - end of string.