string.find()

Now that you understand character classes, you can use them with string.find() to search for patterns instead of exact text. This opens up powerful possibilities for text validation and analysis.

The string.find() function works the same way with patterns as it does with literal strings—it returns the position where the pattern first matches:

local text = "User123"
local position = string.find(text, "%d")
print(position)  -- Output: 5

This finds the first digit in the string, which is at position 5. You can also search for the opposite using uppercase character classes:

local code = "ABC123"
local position = string.find(code, "%D")
print(position)  -- Output: 1

Here, %D matches any non-digit character, so it finds the first letter at position 1.

A common validation task is checking if a string starts with a specific pattern. You can use the anchor ^ at the beginning of a pattern to match only at the start of the string:

local username = "player42"
local startsWithLetter = string.find(username, "^%a")

if startsWithLetter then
    print("Valid username")
else
    print("Username must start with a letter")
end

This pattern checks if the string begins with a letter, making it useful for input validation where certain formats are required.