Lua string manipulation pattern matching alternative "|"

Question

Is there a way I can do a string pattern that will match "ab|cd" so it matches for either "ab" or "cd" in the input string. I know you use something like "[ab]" as a pattern and it will match for either "a" or "b", but that only works for one letter stuff.

Note that my actual problem is a lot more complicated, but essentially I just need to know if there is an OR thing in Lua's string manipulation. I would actually want to put other patterns on each sides of the OR thing, and etc. But if it works with something like "hello|world" and matches "hello, world!" with both "hello" and "world" then it's great!

Answer 1

Using logical operator with Lua patterns can solve most problems. For instance, for the regular expression [hello|world]%d+, you can use

string.match(str, "hello%d+") or string.match(str, "world%d+")

The shortcut circuit of or operator makes sure the string matches hello%d+ first, if if fails, then matches world%d+

Answer 2

Unfortunately Lua patterns are not regular expressions and are less powerful. In particular they don't support alternation (that vertical bar | operator of Java or Perl regular expressions), which is what you want to do.

A simple workaround could be the following:

local function MatchAny( str, pattern_list )
    for _, pattern in ipairs( pattern_list ) do
        local w = string.match( str, pattern )
        if w then return w end
    end
end


s = "hello dolly!"
print( MatchAny( s, { "hello", "world", "%d+" } ) )

s = "cruel world!"
print( MatchAny( s, { "hello", "world", "%d+" } ) )

s = "hello world!"
print( MatchAny( s, { "hello", "world", "%d+" } ) )

s = "got 1000 bucks"
print( MatchAny( s, { "hello", "world", "%d+" } ) )

Output:

hello
world
hello
1000

The function MatchAny will match its first argument (a string) against a list of Lua patterns and return the result of the first successful match.