Remove characters from string [Swift]

Question

there is a line from the console that needs to be displayed in the application. Can anyone suggest how to clear the line?

"\u{1B}[2K\u{1B}[1G\u{1B}[32msuccess\u{1B}[39m Checking for changed pages - 0.000s"

And get in the end:

"success Checking for changed pages - 0.000s"

The real question is (in my opinion): Why does the string contain escape sequences at all? Where do they come from? – Could this be an [XY problem](https://meta.stackexchange.com/q/66377/196432)? — Martin R, Mar 14 '21 at 10:13
We can remove HTML tags. But I have no idea about [2K and [1G symbols. — ARULMOORTHY C, Mar 14 '21 at 10:19
Yes, this is ANSI, ideally I would like to use it for its intended purpose (to set the line color in the application), but first, just get rid of it — Дмитрий Лисин, Mar 14 '21 at 10:29

score 3 · Accepted Answer · answered Mar 14 '21 at 10:38

Use the regular expression mentioned in this answer

let str = "\u{1B}[2K\u{1B}[1G\u{1B}[32msuccess\u{1B}[39m Checking for changed pages - 0.000s"

let regex = try! NSRegularExpression(pattern: "\u{1B}(?:[@-Z\\-_]|\\[[0-?]*[ -/]*[@-~])")
let range = NSRange(str.startIndex..<str.endIndex, in: str)

let cleaned = regex.stringByReplacingMatches(in: str, options: [], range: range, withTemplate: "")
print(cleaned) // "success Checking for changed pages - 0.000s"

Chip Jarred · Answer 2 · 2021-03-15T06:36:26.627

@Gereon's answer is one way to skin the cat. Here's another:

let s = "\u{1B}[2K\u{1B}[1G\u{1B}[32msuccess\u{1B}[39m Checking for changed pages - 0.000s"

guard let r = s.range(of: "Checking for changed pages") else {
    fatalError("Insert code for what to do if the substring isn't found")
}
let cleaned = "success " + String(s[r.lowerBound...])

Here I just literally insert the "success". But if you really need to verify that it's in the string, that can be done too.

guard let r = s.range(of: "Checking for changed pages"), s.contains("success")
else
{
    fatalError("Insert code for what to do if the substring isn't found")
}

To solve the more general problem of removing ANSI escape sequences, you'll need to parse them. Neither my simple solution, nor the regex solution will do it. You'll need to explicitly look for the possible valid codes that follow the escapes.

let escapeSequences: [String] =
    [/* list of escape sequnces */
        "[2K", "[1G", "[32m", "[39m", // etc...
    ]

let escapeChar = Character("\u{1B}")
var result = ""
var i = s.startIndex
outer: while i != s.endIndex
{
    if s[i] == escapeChar
    {
        i = s.index(after: i)
        for sequence in escapeSequences {
            if s[i...].hasPrefix(sequence) {
                i = s.index(i, offsetBy: sequence.distance(from: sequence.startIndex, to: sequence.endIndex))
                continue outer
            }
        }
    }
    else { result.append(s[i]) }
    i = s.index(after: i)
}

print(result)

The thing is, I think ANSI escape sequences can be combined in interesting ways so that what would be multiple escapes can be merged into a single one in some cases. So it can be more complex than just the simple parser I presented.

Remove characters from string [Swift]

2 Answers2