import Foundation
let pattern = #"^app[0-9]+\s=\s\x22([0-9]+)\x22$"#
let regex = try! NSRegularExpression(pattern: pattern, options: .anchorsMatchLines)
let testString = #"""
app1 = "0123456789"
app2 = "1234567890"
app3 = "2345678901"
app4 = "3456789012"
app5 = "4567890123"
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"\1"#
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