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How to run a case-insensitive search for one string inside another

Swift version: 5.1

Paul Hudson    @twostraws   

You can search for one string inside another using the range(of:) method, like this:

let string = "The rain in Spain"
let range1 = string.range(of: "rain")

That returns an optional string index: if the word was found it will say where it was found, otherwise it will be nil.

However, range(of:) does a case-sensitive search by default, which means it will match “rain” but not “Rain” or “RAIN”. If you want a case-insensitive search you need to provide an extra parameter called options, passing it .caseInsensitive:

let range2 = string.range(of: "rain", options: .caseInsensitive)

That returns the same optional value depending on what was found, so you can wrap the whole thing in an if let to see whether a match was found:

if let range3 = string.range(of: "rain", options: .caseInsensitive) {
    // match
} else {
    // no match
}
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