Strings & Patterns

The basics

local s = "Basalt Luak"

print(#s)                    -- 11, length
print(s:upper())              -- BASALT LUAK
print(s:sub(1, 6))            -- Basalt
print(string.format("%s v%d", "Luak", 5))

s:upper() and string.upper(s) are the same call: every string carries the string library as its method table, so colon syntax works directly on string values.

Pattern classes

The building blocks of a Lua pattern:

Uppercasing a class negates it, %A is "not a letter". Quantifiers follow a class or a literal: * (0 or more, greedy), + (1 or more, greedy), - (0 or more, shortest match), ? (0 or 1). ^ and $ anchor to the start and end of the string.

find, match, gmatch, gsub

local s = "version 26.5"

local from, to = string.find(s, "%d+%.%d+")
print(from, to)                            -- 9  13

print(string.match(s, "%d+%.%d+"))         -- 26.5

local replaced, count = string.gsub(s, "%d", "#")
print(replaced, count)                     -- version ##.#  3

for word in string.gmatch("the quick fox", "%a+") do
    print(word)                             -- the / quick / fox, one per iteration
end

Parentheses inside a pattern capture that part of the match. string.match with a capture returns the captured piece instead of the whole match.

local major, minor = string.match("26.5", "(%d+)%.(%d+)")
print(major, minor) -- 26  5

That covers the everyday language. The full standard library, including every function on string, is catalogued in Standard Library once you are ready to start embedding Lua with Luak.