Lua - String find() method

string.find() is one of the primary method of Lua built-in library for pattern matching.

Syntax

start, finish = string.find(s, pattern [, init [, plain]])

Where −

• s − is the string to be searched in.

• pattern − pattern to match

• init − Optional. Index to start the search. Default: 1

• plain − Optional. Boolean value. If true, pattern matching is turned off, and pattern is treated as plain text. Default: false.

Returns

start and end index of the first match found. If no match found, nil is returned.

Example - Usage of String.find() function

main.lua

local text = "Welcome to Lua!"
local pattern = "Lua"

-- search the pattern in text
local start, finish = string.find(text, pattern)

-- if start is not nil
if start then
   print("Pattern found at:", start, "to", finish) -- Prints Pattern found at: 12 to 14
end

pattern = "Programming"

-- search the non-matching pattern in text
local start, finish = string.find(text, pattern)

-- if start is nil
if not start then
   print("Pattern not found.") -- Prints Pattern not found.
end

Output

When we run the above program, we will get the following output−

Pattern found at:       12      to      14
Pattern not found.

Example - Using Special Characters with string.find()

main.lua

local text = "Hello 1234."

-- Search any sequence of digits
local start, finish = string.find(text, "%d+")
print("Digit sequence:", string.sub(text, start, finish)) -- prints Digit sequence: 1234

-- Search a pattern in the beginning of the string
local start, finish = string.find(text, "^Hello")
if start then
  print("Sentence starts with 'Hello'") -- prints Sentence starts with 'Hello'
end

-- Search a pattern at the end of the string
local start, finish = string.find(text, "%d+%$")
if not start then
  print("Sentence does not end with digits.") -- prints Sentence does not end with digits.
end

Output

When we run the above program, we will get the following output−

Digit sequence: 1234
Sentence starts with 'Hello'
Sentence does not end with digits.