Lua .find()

The .find() function is used to search for a substring within a string and returns the start and end indices of the first occurrence of the substring. If the substring is not found, the function returns nil.

Syntax

These are 2 different syntaxes for the .find() function:

string.find(fullString, searchString, init, pattern)

This requires assigning the function to a variable, to return the function.

startindex, endindex = string.find(fullstring, searchstring, init, pattern)

This uses multiple assignments to save the results to individual variables.

• fullString: This is the string being searched through.
• searchString: This is the sub-string to search for.
• init (optional): This is the initial index where the search starts. Default index is 1.
• pattern (optional): This is a Boolean flag indicating whether to search using pattern matching. When set to false, pattern matching can be used, whereas when set to true, pattern matching is ignored, and exact matches are searched for. Default is false.

Note: The special pattern-matching characters allow for lua to use specified characters in searchString to make a pattern-matching search. This allows for complex search patterns, which can enhance the flexibility of your searches. Pattern matching is similar to the concept Regular Expressions, although Lua’s pattern matching is not the same as a regular expression, as it is more limited, and uses a different syntax.

Example

Using .find() without multiple assignments

The below example assigns the function to a unique variable, in order for the results to be returned/printed to the console.

sentence = 'hello world'
search1 = string.find(sentence, "hello")
search2 = string.find(sentence, "world")
search3 = string.find(sentence, "universe")

print(search1)
print(search2)
print(search3)

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The output will be:

1
7
nil

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• hello is found at starting index 1 in the sentence string.
• world is found at starting index 7 in the sentence string.
• universe is not found in sentence string, therefore the output is nil.

Using .find() with multiple assignments

The below example uses multiple assignments to save the results to individual variables, enabling the results to be returned or printed to the console.

sentence = "hello world"
a, b = string.find(sentence, "hello")
print(a)
print(b)

print(a, b)

y, z = string.find(sentence, "world")
print(y)
print(z)

print(y, z)

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The output will be:

1
5
1  5
7
11
7  11

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• hello starts at index 1, and ends at index 5 in the sentence string. Due to multiple assignments, a saves the value 1, and b saves the second value 5.
• world starts at index 7, and ends at index 11 in the sentence string. Due to multiple assignments, y saves the first value 7, and z saves the second value 11.

Using .find() with init (Initial position) parameter

The below example uses the initial position parameter to indicate where the search should start.

sentence1 = 'hello world'
search = string.find(sentence1, "l", 5)
print(search)

sentence2 = 'world world'
a, b = string.find(sentence2, "orl", 5)
print(a)
print(b)

print(a, b)

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The output will be:

10
8
10
8  10

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• l has multiple instances within the sentence string. Due to the init parameter, the search starts at index 5, therefore the first instance of l from index 5 will be at starting index 10.
• orl has multiple instances within the sentence string. Due to the init parameter, the search starts at index 5, therefore the first instance of orl from index 5 will be at starting index 8, and ends at index 10.

Using .find() with pattern (pattern matching) parameter

The below example uses the pattern-matching parameter to determine if pattern-matching characters can be used as search terms.

-- With pattern matching
sentence = "hello world"
a, b = string.find(sentence, "l+", 1, false)
print(a)
print(b)

-- Without pattern matching
y, x = string.find("hello world", "l+", 1, true)
print(y)
print(z)

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The output will be:

3
4
nil
nil

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• In the first example, l+ uses + to match one or more repetitions of the previous character l. Due to the false boolean value, pattern matching is being used, which results in the outputs of a and b resulting in 3 and 4 respectively.
• In the second example, l+ is being treated as a literal string, which doesn’t exist in the string hello world. Due to the true boolean value, pattern matching is disabled, which results in the outputs of nil in both y and z, as the string l+ does not exist in the string hello world.