Split string with specified delimiter in lua

When splitting strings, the easiest way to avoid corner cases is to append the delimiter to the string, when you know the string cannot end with the delimiter:

str = "a,b,c,d,e,f,g"
str = str .. ','
for w in str:gmatch("(.-),") do print(w) end

Alternatively, you can use a pattern with an optional delimiter:

str = "a,b,c,d,e,f,g"
for w in str:gmatch("([^,]+),?") do print(w) end

Actually, we don't need the optional delimiter since we're capturing non-delimiters:

str = "a,b,c,d,e,f,g"
for w in str:gmatch("([^,]+)") do print(w) end

Here's my go-to split() function:

-- split("a,b,c", ",") => {"a", "b", "c"}
function split(s, sep)
    local fields = {}
    
    local sep = sep or " "
    local pattern = string.format("([^%s]+)", sep)
    string.gsub(s, pattern, function(c) fields[#fields + 1] = c end)
    
    return fields
end