Introduction To Regular Expressions In Objective-C: Search String For Email Addresses

January 14, 2013

Regular expressions (aka regex) are extremely powerful for string matching, if you are not familiar with how to use them, I highly recommend you take some time to learn more.

To give you a taste, below is a block of code that uses the NSRegularExpression and NSTextCheckingResult classes to create a compiled regular expression and extract content from the same.

The example will search for all email addresses numbers in the following string:

NSString *str = @"Sed ut perspiciatis, MobileDeveloperTips@fubar.net unde omnis iste
 natus error youremail@xyz123abc.com sit voluptatem accusantium doloremque laudantium,
 totam rem aperiam eaque ipsa, quae ab illo inventore veritatis et quasi architecto
 beatae vitae dicta sunt, anotherEmailAddress@SomeServer.info explicabo.";

The output we are after:

MobileDeveloperTips@fubar.net
youremail@xyz123abc.com
anotherEmailAddress@SomeServer.info

Here is the code to create the regex and parse the results:

NSError *error = nil;
 
// String to search
NSString *str = @"Sed ut perspiciatis, MobileDeveloperTips@fubar.net unde omnis iste natus error youremail@xyz123abc.com sit voluptatem accusantium doloremque laudantium, totam rem aperiam eaque ipsa, quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt, anotherEmailAddress@SomeServer.info explicabo.";
 
// Regular expression to parse email
NSString *regexAsString = @"([a-zA-Z0-9_\\-\\.\\+])+\\@([a-zA-Z0-9_\\-\\.])+\\.([A-Za-z]+)";
 
// Create instance of NSRegularExpression
// which is a compiled regular expression pattern
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regexAsString options:0 error:&error];
 
// If no errors
if (!error)
{
  // Array of matches of regex in string
  NSArray *results = [regex matchesInString:str options:0 range:NSMakeRange(0, str.length)];
 
  // View results to see range and length of matches
  NSLog(@"results: %@", results);
 
  int count = 1;
  // For each item found...
  for (NSTextCheckingResult *entry in results)
  {
    // Get email from the str using range 
    NSString *text = [str substringWithRange:entry.range];
 
    NSLog(@"Result %d: - %@", count++, text);
  }
}
else
  NSLog(@"Invalid epxression pattern: %@", error);

The complete output is below:

results: (
    "<NSExtendedRegularExpressionCheckingResult: 0x845c5d0>{21, 29}{<NSRegularExpression: 0x845b400> ([a-zA-Z0-9_\\-\\.\\+])+\\@([a-zA-Z0-9_\\-\\.])+\\.([A-Za-z]+) 0x0}",
    "<NSExtendedRegularExpressionCheckingResult: 0x845c810>{79, 23}{<NSRegularExpression: 0x845b400> ([a-zA-Z0-9_\\-\\.\\+])+\\@([a-zA-Z0-9_\\-\\.])+\\.([A-Za-z]+) 0x0}",
    "<NSExtendedRegularExpressionCheckingResult: 0x845c6c0>{261, 35}{<NSRegularExpression: 0x845b400> ([a-zA-Z0-9_\\-\\.\\+])+\\@([a-zA-Z0-9_\\-\\.])+\\.([A-Za-z]+) 0x0}"
)
2013-01-13 22:32:11.035 Sandbox[4492:c07] Result 1: - MobileDeveloperTips@fubar.net
2013-01-13 22:32:11.036 Sandbox[4492:c07] Result 2: - youremail@xyz123abc.com
2013-01-13 22:32:11.037 Sandbox[4492:c07] Result 3: - anotherEmailAddress@SomeServer.info

Notice the range specified in the results, for example, {21, 29}, this is the location of the first match, position 21, the match is 29 characters long (MobileDeveloperTips@fubar.net).

Pretty slick isn’t it.