Lua:
Converting a string to lower case

How to:

In Lua, you lighten your load with string.lower(). Feed it a string, out pops the lowercase version. Observe:

local originalString = "Hello, World!"
local lowerCaseString = string.lower(originalString)
print(lowerCaseString)  -- Output: hello, world!

Run this snippet. The shouty capitals are now whisper-level lowercase.

Deep Dive

Since the dawn of computing, folks have needed to smoosh text into a uniform case for all sorts of reasons, like sorting or case-insensitive logins. In Lua, string.lower() has been the go-to since its inception. It’s neat, it’s built-in, and it does its job without fuss.

But what’s under the hood? string.lower() hustles through each character, and if it’s uppercase (A through Z), it converts it. Lua relies on the ASCII values: ‘A’ (65) through ‘Z’ (90) get bumped to ‘a’ (97) through ‘z’ (122). The difference? 32. So, lowercase = uppercase + 32.

What if string.lower() feels too mainstream? You could manually trudge through characters with a loop, using ASCII values, or pattern matching with string.gsub():

local s = "Make Me Lowercase, Please"
s = s:gsub("%u", function (upper) return string.char(upper:byte() + 32) end)
print(s)  -- Output: make me lowercase, please

But really, why row your boat when you’ve got an outboard motor (read: string.lower())?

See Also

Dig deeper into Lua’s string manipulation with these goodies:

• Programming in Lua (4th edition) for the ins, outs, and in-betweens of strings.
• Lua 5.4 Reference Manual for all the string functions when you’re ready to go beyond lowercase.