An introduction to regular expressions (pattern matching)

This lesson covers the basics of pattern matching with regular expressions in Objective-C, with the aim of checking whether a string fits a fixed format.

A regular expression is a special notation describing the shape of a string. You specify a pattern such as "three digits, a hyphen, four digits" and then test whether a string matches it or pull the matching part out. You use the NSRegularExpression class.

The sample code compiles a phone-number-shaped pattern with [NSRegularExpression regularExpressionWithPattern:...] and finds a match with firstMatchInString:. Note that backslashes have to be double-escaped inside the pattern string.

A common early stumble is remembering what the symbols mean. It looks like nothing but punctuation at first, but it is a powerful tool for tasks such as validating an email address.

In professional work, regular expressions are valued as a broadly transferable skill — learn them once and they work across most programming languages.

📖 Reference code

NSString *text = @"Phone: 090-1234-5678";
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"\\d{3}-\\d{4}-\\d{4}" options:0 error:nil];
NSTextCheckingResult *match = [regex firstMatchInString:text options:0 range:NSMakeRange(0, text.length)];
NSLog(@"%@", [text substringWithRange:match.range]);

NSRegularExpression *regex2 = [NSRegularExpression regularExpressionWithPattern:@"^\\d+$" options:0 error:nil];
NSUInteger count = [regex2 numberOfMatchesInString:@"12345" options:0 range:NSMakeRange(0, 5)];
NSLog(@"%@", count > 0 ? @"true" : @"false");

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