Swift regex: does a string match a pattern?

Question

In Swift, what is a simple way to see if a string matches a pattern?

Pseudocode examples:

if string matches pattern ...

if string =~ pattern ...

(I have read the Swift docs and haven't seen a regex capability. I've read about adding a new =~ operator which is a good idea yet more complex than I'd like because this is for a teaching project. I have tried rangeOfString but get the error: 'String' does not have a member 'rangeOfString'. I am looking for a Swift solution, i.e. not typing NSRegularExpression. I do not need to do anything with the match result data.)

@picciano Thanks for the link - I added a clarification that this question is different than the linked one because I want to use just Swift terms, not NSRegularExpression. — joelparkerhenderson
– joelparkerhenderson, Commented Apr 21, 2015 at 23:52

joelparkerhenderson · Accepted Answer · 2017-11-18 05:25:02Z

84

Swift version 3 solution:

if string.range(of: regex, options: .regularExpression, range: nil, locale: nil) != nil ...

Swift version 2 solution:

if string.rangeOfString(pattern, options: .RegularExpressionSearch) != nil ...

Example -- does this string contain two letter "o" characters?

"hello world".rangeOfString("o.*o", options: .RegularExpressionSearch) != nil

Note: If you get the error message 'String' does not have a member 'rangeOfString', then add this before: import Foundation. This is because Foundation provides the NSString methods that are automatically bridged to the Swift String class.

import Foundation

Thanks to Onno Eberhard for the Swift 3 update.

edited Nov 18, 2017 at 5:25

answered Apr 21, 2015 at 22:40

joelparkerhenderson

35.6k20 gold badges103 silver badges122 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Iulian Onofrei Over a year ago

Why not use regex.firstMatch(in: string, options: [], range: NSRange(location: 0, length: string.count)) != nil? Isn't it semantically clearer than range(of:options:range:locale:).

Onno Eberhard · Accepted Answer · 2017-07-18 12:30:47Z

63

The solutions mentioned above didn't work for me anymore, so I'm posting my solution here (I used an extension for String):

extension String {
    func matches(_ regex: String) -> Bool {
        return self.range(of: regex, options: .regularExpression, range: nil, locale: nil) != nil
    }
}

Example:

if str.matches("^[a-zA-Z0-9._-]{1,30}$") {
    //...
}

answered Jul 18, 2017 at 12:30

Onno Eberhard

1,6011 gold badge13 silver badges18 bronze badges

2 Comments

naeemjawaid Over a year ago

Check out reference, examples and live demo of Regular Expression at: regexr.com

Karthick Ramesh Over a year ago

You saved my 4 hours. The reusable method was so helpful.

David Berry · Accepted Answer · 2015-04-22 04:39:40Z

16

To get the syntax you actually ask about, you can easily define a new operator which wraps the bridged NSString functionality:

infix operator =~ {}
func =~(string:String, regex:String) -> Bool {
    return string.rangeOfString(regex, options: .RegularExpressionSearch) != nil
}

"abcd" =~ "ab*cd"
"abcd" =~ "abcde+"

answered Apr 22, 2015 at 4:39

David Berry

41.3k12 gold badges87 silver badges96 bronze badges

1 Comment

joelparkerhenderson Over a year ago

Thanks David. For this particular project I'm looking for a solution that doesn't define a new operator. (It would be great if Swift added your idea to the entire language, IMHO)

Carl Younger · Accepted Answer · 2025-07-24 17:50:27Z

Swift 5.7 introduced regex literals, regex result builders (RegexBuilder) and better Swift types (Regex) and APIs for working with them. So (for example) you could match a whole string with something like this:

let decimalNumber = #/
    [+|-]?
    [0-9]([0-9_]*[0-9])?
    (\.[0-9]([0-9_]*[0-9])?)?
/#

if myString.wholeMatch(of: decimalNumber) != nil { /* myString is a decimal */ }

Note: You don't need to start the regex with ^ or end on $, as the wholeMatch method only matches the whole string its called on.

String also provides methods for matching the start of the string et cetera, and Regex provides a full suite of equivalent methods.

Note: If you right-click a regex in XCode, you can translate it to the RegexBuilder DSL. The builder is much more verbose, but can be a lot less cryptic in many cases (though sometimes it's worse).

Peter · Accepted Answer · 2018-11-02 17:09:26Z

-1

In Swift 4.2 the following doesn't return nil even if the string does not match the pattern:

string.range(of: regex, options: .regularExpression, range: nil, locale: nil)

As Xcode suggests:

Comparing non-optional value of type 'NSRange' (aka '_NSRange') to nil always returns true

Therefore what I ended up using is:

if string.range(of: regex, options: .regularExpression)
        .location != NSNotFound {
    // do stuff if string matches regexp
}

edited Nov 2, 2018 at 17:09

answered Nov 2, 2018 at 17:03

Peter

93 bronze badges

1 Comment

Sulthan Over a year ago

You are calling that method on NSString, not on String, that's your problem. Your solution is technically correct for NSString but you can also just do (string as String).range(of: ...) != nil.

Collectives™ on Stack Overflow

Swift regex: does a string match a pattern?

5 Answers 5

1 Comment

2 Comments

1 Comment

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

2 Comments

1 Comment

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related