Split a string using string.gmatch() in Lua

Question

There are some discussions here, and utility functions, for splitting strings, but I need an ad-hoc one-liner for a very simple task.

I have the following string:

local s = "one;two;;four"

And I want to split it on ";". I want, eventually, go get { "one", "two", "", "four" } in return.

So I tried to do:

local s = "one;two;;four"

local words = {}
for w in s:gmatch("([^;]*)") do table.insert(words, w) end

But the result (the words table) is { "one", "", "two", "", "", "four", "" }. That's certainly not what I want.

Now, as I remarked, there are some discussions here on splitting strings, but they have "lengthy" functions in them and I need something succinct. I need this code for a program where I show the merit of Lua, and if I add a lengthy function to do something so trivial it would go against me.

Answer 1

local s = "one;two;;four"
local words = {}
for w in (s .. ";"):gmatch("([^;]*);") do 
    table.insert(words, w) 
end

By adding one extra ; at the end of the string, the string now becomes "one;two;;four;", everything you want to capture can use the pattern "([^;]*);" to match: anything not ; followed by a ;(greedy).

Test:

for n, w in ipairs(words) do
    print(n .. ": " .. w)
end

Output:

1: one
2: two
3:
4: four

Answer 2

Just changing * to + works.

local s = "one;two;;four"
local words = {}
for w in s:gmatch("([^;]+)") do 
    table.insert(words, w) 
    print(w)
end

The magic character * represents 0 or more occurrene, so when it meet ',', lua regarded it as a empty string that [^;] does not exist.

Sorry for my carelessness, the words[3] should be a empty string, but when I run the original code in lua5.4 interpreter, everything works.

code here

running result here (I have to put links because of lack of reputation)

Answer 3

function split(str,sep)
    local array = {}
    local reg = string.format("([^%s]+)",sep)
    for mem in string.gmatch(str,reg) do
        table.insert(array, mem)
    end
    return array
end
local s = "one;two;;four"
local array = split(s,";")

for n, w in ipairs(array) do
    print(n .. ": " .. w)
end

result:

1:one

2:two

3:four