import Foundation
let pattern = ##"""
(?xsm) # free-spacing mode, multi-line
(?=.*?pig) # fail right away if pig isn't there
(?=
( # Group 1
(?: # skip one line that doesn't have pig
^ # beginning of line
(?:(?!pig)[^\r\n])* # zero or more chars not followed by pig
(?:\r?\n) # newline chars
)
(?:(?1)|[^:]+) # recurse Group 1 OR match all chars that are not a :
(:\d+) # match a sequence of digits
)? # End Group 1
) # End lookahead. Group 1, if set, now contains the number of lines skipped
.*?\Kpig # match pig
(?=.*?(?(2)\2):(\d+))
"""##
let regex = try! NSRegularExpression(pattern: pattern)
let testString = #"""
my cat pi g
dog pi g
my pig
my cow
my mouse
:1:2:3:4:5:6:7
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"\3"#
let lookupRange = (testString as NSString).range(of: pattern, options: .regularExpression, range: stringRange)
if lookupRange.intersection(stringRange) != nil {
let result = regex.stringByReplacingMatches(in: testString, range: lookupRange, withTemplate: substitutionString)
print(result)
} else {
print("No matches were found.")
}
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