Swift Regex to check if String is Amount format (2x, 3x,...)

Question

I would like to check if a given String is in a amount format. A few examples for a better understanding:

Should return true:

2x

31x

3x abcd

Should return false:

2x3

3xabc

asdf3x

So in general: it has to start with a number (0-9), can be more digits. Right after the number a "x"/"X" should follow and after the "x"/"X" should be the end or a white space.

I am struggling to get this done.. This is what I tried:

func isAmountFormat() -> Bool {
    return self.matches("[0-9]+[X,x]")
}

Can anyone help me out here?

@Thefourthbird that gives `invalid escape sequence in literal` . — Chris, Jan 15 '21 at 19:59
@Thefourthbird I think this is working. One more thing: Do you know how I can extract the number before the x from a given String in this format?? — Chris, Jan 15 '21 at 20:06
Using a capture group `\\b([0-9]+)[Xx]\\b` see https://regex101.com/r/Y2DNT9/1 — The fourth bird, Jan 15 '21 at 20:08
My swift knowlegde is at a minimum, but [this page](https://stackoverflow.com/questions/42789953/swift-3-how-do-i-extract-captured-groups-in-regular-expressions) for example has some examples. — The fourth bird, Jan 15 '21 at 20:20
@Thefourthbird one last thing! "0x" should not be valid, but "1x" or "100x" should be valid. What do I have to change then ? — Chris, Jan 15 '21 at 21:29
Use `"(?i)\\b[1-9][0-9]*x\\b"`. Could you describe what you mean by "amount format" to get an answer? — Wiktor Stribiżew, Jan 15 '21 at 21:36

score 1 · Accepted Answer · answered Jan 15 '21 at 21:41

You may use

"(?i)\\b[1-9][0-9]*x\\b"

See the regex demo. Details:

(?i) - case insensitive flag (in case you cannot pass the .caseInsensitive in your current regex matching method)
\b - a word boundary
[1-9] - a non-zero digit
[0-9]* - any zero or more digits
x - an X or x
\b - a word boundary.

See a Swift snippet:

let test = "3x abcd"
if test.range(of: "\\b[1-9][0-9]*x\\b", options: [.regularExpression, .caseInsensitive]) != nil {
    print("Matched")
} else {
   print("No match")
}

Note that if the match should occur at the start of the string, you may compile the regex object with the .anchored option, or replace the first \\b with ^.

Swift Regex to check if String is Amount format (2x, 3x,...)

1 Answers1