Lua Strings: Literals, Concatenation, Bytes and UTF-8

Lua strings are immutable byte sequences. They may contain ordinary text, binary data, and zero bytes. An operation never modifies an existing string; it returns a new one.

local original = "one string"
local changed = original:gsub("one", "another")
print(original) -- one string
print(changed)  -- another string

Literals and concatenation

Single- and double-quoted literals support escapes such as \n, \t, \\, and numeric byte escapes. Long brackets are convenient for multiline text:

local document = [[
first line
second line
]]

local label = "Lua " .. "strings"

Concatenating many fragments in a loop repeatedly creates intermediate strings. Collect fragments in a table and use table.concat(parts) for large output.

Length and conversion

print(#"Lua")              -- 3 bytes
print(tonumber("42"))      -- 42
print(tonumber("ff", 16))  -- 255
print(tostring(3.14))

Arithmetic may coerce numeric strings in some Lua versions, but explicit tonumber is clearer and more portable. The length operator counts bytes, not Unicode characters.

Standard operations

local text = "Hello Lua"
print(text:sub(1, 5))
print(text:upper())
print(text:find("Lua", 1, true)) -- plain search
print(("x=%d"):format(12))

Other core functions include string.byte, string.char, string.rep, string.reverse, string.match, string.gmatch, and string.gsub.

Lua 5.3 and later include utf8 helpers such as utf8.len, utf8.codes, and utf8.char. They operate on UTF-8 code points, which are still not always the same as user-perceived characters. Use a Unicode library for normalization, locale-aware case conversion, or grapheme-cluster editing.