Swift Regular Expression Special Characters

Question

I'm currently using a regular expression to find some files my app previously created, but I have problems with german "Umlauten" like ö,ä,ü. My expression doesn't match if there are "Umlaute" in the string. I guess it has something to do with the locale, but I can't figure it out what locale to set (already tried nil).

Here's some code:

// Building the regex
var regex = somePrefix + "_("
for string in stringArray{     
     regex += string + "|"  // string can contain öäü
}
regex.remove(at: regex.index(before: regex.endIndex))
regex += ")_w\\d_d\\d"

// Finding files
let fileManager = FileManager()
let files = fileManager.enumerator(atPath: somePath)
while let file = files?.nextObject() {
   let fileName = file as! String            
   if fileName.range(of: regex, options: .regularExpression, range: nil, locale: Locale.current) != nil {
   print(fileName + " found")
   }
}

// Some example that didn't match:

Regex = reis 8_(Ibedir|Drölf )_w\d_d\d
Filename that didnt match = reis 8_Drölf _w0_d0.plist

This might help, those characters are unicode: https://stackoverflow.com/questions/29756530/swift-regex-matching-fails-when-source-contains-unicode-characters — sniperd, Jan 03 '18 at 14:27
Can you give a concrete example of a file name and a pattern which does not match as expected? — Martin R, Jan 03 '18 at 14:33
It could be a Unicode normalization issue. Try adding `.decomposedStringWithCanonicalMapping` to the filename and/or the pattern. — Martin R, Jan 03 '18 at 14:50
Adding it to both did the trick. Post it as an answer and I'll accept it. — LarsGvB, Jan 03 '18 at 14:57

score 1 · Accepted Answer · answered Jan 03 '18 at 15:03

Apparently the file names use a different Unicode normalization form than the given strings. The Unicode Regular Expression Guidelines: 3.2 Canonical Equivalents suggest:

Before (or during) processing, translate text (and pattern) into a normalized form. This is the simplest to implement, since there are available code libraries for doing normalization.

This can be achieved by applying .decomposedStringWithCanonicalMapping to both the pattern and the file name.

Swift Regular Expression Special Characters

1 Answers1