import Foundation
let pattern = ##"""
(?xsm) # free-spacing mode, multi-line
(?=.*?pig) # lookahead: if pig is not there, fail right away to save the effort
(?: # start counter-line-skipper (lines that don't include pig)
(?: # 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
)
# for each line skipped, let Group 1 match an ever increasing portion of the numbers string at the bottom
(?= # lookahead
[^:]+ # skip all chars that are not colons
( # start Group 1
(?(1)\1) # if Group 1 is set, match Group 1
# (?>\1?) # alternate phrasing for the above
:\d+ # match a colon and some digits
) # end Group 1
) # end lookahead
)*+ # end counter-line-skipper: zero or more times
.*? # match
\K # drop everything we've matched so far
pig # match pig (this is the match!)
(?=[^:]+(?(1)\1):(\d+)) # capture the next number to Group 2
"""##
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 = #"\2"#
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