Lua:
Extracting substrings

How to:

In Lua, use the string.sub function:

local text = "Hello, Lua!"
-- Extract 'Hello'
print(string.sub(text, 1, 5)) -- Output: Hello

-- Grab 'Lua'
print(string.sub(text, 8, 11)) -- Output: Lua

Or get the last characters with negative indices:

-- Snag 'Lua!' from the end
print(string.sub(text, -4)) -- Output: Lua!

Use patterns to find and extract:

local phrase = "The quick brown fox jumps"
-- Match and extract 'quick'
print(phrase:match("(%a+) quick")) -- Output: The

Deep Dive

In early programming, string handling was manual and clunky, often needing loops and conditionals. Lua’s string.sub is part of its richer string library, making string manipulation a breeze. Alternatives to string.sub include pattern matching with string.match, which is more powerful but can be overkill for simple tasks.

The string.sub and pattern matching are based on C functions due to Lua’s C roots. You won’t find a vast standard library in Lua for strings compared to languages like Python; it sticks to essentials, valuing simplicity and efficiency. Remember, indices in Lua start at 1, not 0.

See Also

• Lua 5.4 Reference Manual on Strings: www.lua.org/manual/5.4/manual.html#6.4
• ‘Programming in Lua’ (4th edition), especially the chapter on strings: www.lua.org/pil/contents.html