Regular expression doesn't work in Swift, but work in other languages

Question

I know that NSRegularExpression works on Unicode code points and (normal) JavaScript regex works on UTF-16 code units, but I don't know what should I change in my regex.

Regex: <text[^>]+>([^<]+)<\/text>

Works here: regex101

My parsing method:

func parseCaptions(text: String) -> String? {
        let textRange = NSRange(location: 0, length: text.count)
        let regex = try! NSRegularExpression(pattern: "<text[^>]+>([^<]+)<\\/text>")
        let matches = regex.matches(in: text, range: textRange)
        
        var result: String?
        
        for match in matches {
            let range = match.range
            
            let first = text.index(text.startIndex, offsetBy: range.location)
            let last = text.index(text.startIndex, offsetBy: range.location + range.length)
            
            var string = String(text[first...last])
            
            string = string.replacingOccurrences(of: "\n", with: " ")
            string = string.replacingOccurrences(of: "&amp;#39;", with: "'")
            string = string.replacingOccurrences(of: "&amp;quot;", with: "\"")
            string.append("\n")
            
            result = string
        }
        
        return result
    }

do you really need the answer to be a regex solution, or are you open to an simple alternative to achieve what you want? — workingdog support Ukraine, Jul 28 '22 at 10:46
It's probably better to use an actual XML parser than just regex? — qrsngky, Jul 28 '22 at 10:49
Side stepping the issues with the regex, [you can’t parse html or xml with regular expressions](https://stackoverflow.com/a/1732454/3141234). You should use the right tool for the job, which is a proper parser. — Alexander, Jul 28 '22 at 11:04
@Larme thanks, it work but it also adds lines in which nothing is found — Dewerro, Jul 28 '22 at 11:21
Your expected output wasn't clear. That's why I asked for it. https://pastebin.com/rAgsnCYJ should do the trick... — Larme, Jul 28 '22 at 11:30

score 1 · Accepted Answer · answered Aug 02 '22 at 15:41

It's not the Regex the issue, it's what you do with the matches.

You do:

var result: String?

for match in matches {
    let range = match.range
    let first = text.index(text.startIndex, offsetBy: range.location)
    let last = text.index(text.startIndex, offsetBy: range.location + range.length)

    var string = String(text[first...last])
    ...
    result = string
}
return result

So you're overwriting each time result with the last match.

A solution:

func parseCaptions(text: String) -> String {
    //NSRange, based on NSString use UTF16 for counting, while Swift.String use UTF8 by default, so `text.count` might be wrong
    let textRange = NSRange(location: 0, length: text.utf16.count)
    let regex = try! NSRegularExpression(pattern: "<text[^>]+>([^<]+)<\\/text>")
    let matches = regex.matches(in: text, range: textRange)

    var result: String = ""
    for match in matches {
        let textNSRange = match.range(at: 1)
        let textRange = Range(textNSRange, in: text)!
        var string = String(text[textRange])
        string = string.replacingOccurrences(of: "\n", with: " ")
        string = string.replacingOccurrences(of: "&#39;", with: "'")
        string = string.replacingOccurrences(of: "&amp;quot;", with: "\"")
        string.append("\n")
        result.append(string)
    }
    return result
}

So, with input:

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<transcript>
<text start="9.462" dur="1.123">Aaaah</text>
<text start="70.507" dur="5.51">So guys, apparently we control Rewind this year.</text>
<text start="76.017" dur="4.842">
Y&#39;all we can do whatever we want. What do we do?
</text>
</transcript>

We get:

Aaaah
So guys, apparently we control Rewind this year.
 Y'all we can do whatever we want. What do we do?

Regular expression doesn't work in Swift, but work in other languages

1 Answers1