import Foundation
let pattern = #"^\s*\[(?P<id>\d+)\]\s*:\s*(?P<link>[^\n]+)$"#
let regex = try! NSRegularExpression(pattern: pattern, options: .anchorsMatchLines)
let testString = #"""
This is a sample doucument that would have inline links.
[Example 0][0], [Example 1][1], [Example 2][2] , [Example 3][3] , [Example 4][4]
[0]: http://example.com
[1]: http://example.com/1
[2] : http://example.com/2
[3]: http://example.com/3
[4] : http://example.com/4
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"[\1]: \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