import Foundation
let pattern = #"3(?:\.\d+)*\.\s*"#
let regex = try! NSRegularExpression(pattern: pattern)
let testString = #"""
3.1. Cre
3.1.1. Im
3.1.1.1. O
3.1.1.2. Ce
3.1.1.3. Part
3.1.2. ED
3.1.2.1. Ow
3.1.2.2. ED
3.1.3. OF
3.1.3.1. O
3.1.3.2. O
3.1.3.3. O
3.1.3.4. O
3.1.4. Sc
3.1.5. In
3.1.6. Vi
3.1.7. Bu
3.1.8. Ho
3.1.8.1. Ou
3.1.8.2. In
3.1.9. Pa
3.1.9.1. Re
3.1.9.2. Re
3.1.9.3. Pr
3.1.9.3.1. Ou
3.1.9.3.2. Sp
3.1.9.3.3. In
3.1.9.3.4. In
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"\t"#
let result = regex.stringByReplacingMatches(in: testString, range: stringRange, withTemplate: substitutionString)
print(result)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Swift 5.2, please visit: https://developer.apple.com/documentation/foundation/nsregularexpression