String Functions

The string library's functions can be called two ways: string.upper(s) or, with method syntax, s:upper().

local s = "Hello, Lua World"

print(string.upper(s))
print(s:upper())
print(s:lower())
print(s:len())
print(s:sub(1, 5))
print(s:sub(-5))
print(s:rep(2, " | "))
print(s:reverse())
print(("x"):rep(3))

HELLO, LUA WORLD
HELLO, LUA WORLD
hello, lua world
16
Hello
World
Hello, Lua World | Hello, Lua World
dlroW auL ,olleH
xxx

• s:sub(i, j) extracts characters i to j — 1-based and inclusive. Negative positions count from the end.
• A string literal needs parentheses to call a method: ("x"):rep(3).

Finding and replacing

local s = "The quick brown fox"

print(s:find("quick"))
print(s:find("slow"))
print(s:find("o", 1, true))
print(s:gsub("o", "0"))
print((s:gsub("quick", "slow")))
print(s:match("%a+$"))

5	9
nil
13	13
The quick br0wn f0x	2
The slow brown fox
fox

• find returns the start and end positions, or nil.
• gsub returns the new string and the number of replacements. Wrap it in parentheses to keep only the string.
• find, gsub, and match use patterns (%a+$ means "letters at the end") — a simpler cousin of regular expressions, covered in Level 2. Passing true as the fourth argument to find searches for plain text.

Splitting and trimming

Lua has no built-in split or trim, but patterns make them one line:

local csv = "red, green ,blue"
for item in csv:gmatch("[^,]+") do
  local trimmed = item:match("^%s*(.-)%s*$")
  print("[" .. trimmed .. "]")
end

[red]
[green]
[blue]

gmatch loops over every match; [^,]+ means "one or more characters that aren't commas".

Characters and codes

print(string.byte("A"))
print(string.char(72, 105))
print(("abc"):byte(1, -1))

65
Hi
97	98	99