import Foundation
let pattern = #"(?s)(?:^([^"]*(?:"[^"a]*(?=")"[^"]*(?="))*"[^"a]*)|(?!^)\G)a([^"a]*(?:(?=a.*?")|(?:"[^"]*$|"[^"]*(?=")(?:"[^"a]*(?=")"[^"]*(?="))*"[^"a]*)))"#
let regex = try! NSRegularExpression(pattern: pattern)
let testString = #"""
Somebody once told me "apples" are good for you
=> Somebody once told me "bpples" are good for you
"Aardvarks" make good kebabs
=> "Abrdvbrks" make good kebabs
The boy said "aaah!" when his mom told him he was eating aardvark
=> The boy said "bbbh!" when his mom told him he was eating aardvark
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"$1b$2"#
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