Intro to String Patterns

When you used string.gsub() in the previous lesson, you searched for exact text like spaces or specific words. But what if you need to find "any digit" or "any letter" without knowing the exact character? This is where string patterns come in.

String patterns in Lua are a way to describe what kind of text you're looking for, rather than the exact text itself. They're simpler than regular expressions but powerful enough for most text-processing tasks.

Lua provides special codes called character classes that match categories of characters. Here are the most common ones:

%d  -- matches any digit (0-9)
%a  -- matches any letter (a-z, A-Z)
%s  -- matches any whitespace (space, tab, newline)
%w  -- matches any alphanumeric character (letters and digits)
%p  -- matches any punctuation character

Here's how you might use these patterns with string.find() to locate the first digit in a string:

local text = "Room 42 is available"
local position = string.find(text, "%d")
print(position)  -- Output: 6

You can also use uppercase versions of these classes to match the opposite. For example, %D matches any character that is not a digit, and %A matches any character that is not a letter.