Search through NSString using Regular Expression

How might I go about searching/enumerating through an NSString using a regular expression?

A regular expression such as: /(NS|UI)+(\w+)/g.

You need to use NSRegularExpression class.

Example inspired in the documentation:

NSString *yourString = @"";
NSError *error = NULL;
NSRegularExpression *regex = [NSRegularExpression         
    regularExpressionWithPattern:@"(NS|UI)+(\\w+)"
    options:NSRegularExpressionCaseInsensitive
    error:&error];
[regex enumerateMatchesInString:yourString options:0 range:NSMakeRange(0, [yourString length]) usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop){
    // your code to handle matches here
}];

If you just want to match some pattern in string, there is a simple way to test Regular Expression with NSString:

NSString *string = @"Telecommunication";

if ([string rangeOfString:@"comm" options:NSRegularExpressionSearch].location != NSNotFound)

    NSLog(@"Got it");

else

    NSLog(@"No luck");

Note, often you'll want ...

if ([string rangeOfString:@"cOMm"
  options:NSRegularExpressionSearch|NSCaseInsensitiveSearch].location
  != NSNotFound)
     NSLog(@"yes match");

In Swift you may write code like this ...

Swift 2

    let string = "Telecommunication"

    if string.rangeOfString("cOMm", options: (NSStringCompareOptions.RegularExpressionSearch | NSStringCompareOptions.CaseInsensitiveSearch)) != nil {
        print("Got it")
    } else {
        print("No luck")
    }

Swift 4

    let string = "Telecommunication"

    if string.range(of: "cOMm", options: [.regularExpression, caseInsensitive]) != nil {
        print("Got it")
    } else {
        print("No luck")
    }

Please take note that Swift 2's rangeOfString(_:,options:) and Swift 4's range(of:options:) return Range<String.Index>? that returns nil if search failed