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NSRegularExpression: How to match regular expressions in strings

Swift version: 5.1

Paul Hudson    @twostraws   

The NSRegularExpression class lets you find and replace substrings using regular expressions, which are concise and flexible descriptions of text. For example, if we wanted to pull "Taylor Swift" out of the string "My name is Taylor Swift", we could write a regular expression that matches the text "My name is " followed by any text, then pass that to the NSRegularExpression class.

The example below does just that. Note that we need to pull out the second match range because the first range is the entire matched string, whereas the second range is just the "Taylor Swift" part:

do {
    let input = "My name is Taylor Swift"
    let regex = try NSRegularExpression(pattern: "My name is (.*)", options: NSRegularExpression.Options.caseInsensitive)
    let matches = regex.matches(in: input, options: [], range: NSRange(location: 0, length: input.utf16.count))

    if let match = matches.first {
        let range = match.range(at:1)
        if let swiftRange = Range(range, in: input) {
            let name = input[swiftRange]
        }
    }
} catch {
    // regex was bad!
}

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Available from iOS 4.0

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