Validate String With Regex

Question

I'm trying to validate a string with this regex

var regexAgencia = new Regex("^(?!0000)([0-9]{4})");
var result = regexAgencia.IsMatch(agencia);

Valid Options:

N-X
NN-X
NNN-X
NNNN-X
N
NN 
NNN 
NNNN

Invalid Options:

0-X 
00-X 
000-X 
0000-X
0
00
000
0000

Where N is any number 0-9 and X can be X or 0-9

When I validade this "014777417" the regex return true

I need help to write a regex to validade this string with this rules.

You need to describe your problem more detailed, I realy don't know why do you think 014777417 shouldn't match regexp ^(?!0000)([0-9]{4}) which mean: if( begins with not "0000" and have 4 digits ) — sTrenat
– sTrenat, Commented Jul 24, 2018 at 10:39
What is the question? Why are these options invalid? Is it leading zeros? — Mirco Gericke
– Mirco Gericke, Commented Jul 24, 2018 at 10:39
what is N and what is X in your rule? Does - should be in text or it's just to visualise? — sTrenat
– sTrenat, Commented Jul 24, 2018 at 10:41
N is any number between 0 and 9 and X can be X or any number between 0 and 9 — b3r3ch1t
– b3r3ch1t, Commented Jul 24, 2018 at 10:43

SamWhan · Accepted Answer · 2018-07-24 11:10:04Z

2

This should do it for you:

^(?=\d*[1-9])\d{1,4}(?:-[X\d])?$

It starts with a positive look ahead to ensure a digit other than zero is present ((?=\d*[1-9])). Thereafter it matches 1-4 digits, optionally followed by a hyphen and a digit or X.

See it here at regex101.

edited Jul 24, 2018 at 11:10

answered Jul 24, 2018 at 11:01

SamWhan

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Comments

Hambone · Accepted Answer · 2018-07-24 10:48:03Z

0

You certainly can do this through just Regex, however, I always have this lingering fear of creating code that either:

1) only I understand or remember 2) even I don't understand when looking back

In that spirit, it seems if you do a simple split, your string might be easier to evaluate:

string[] parts = agencia.Split('-');
if ((parts.Length == 1 && Regex.IsMatch(agencia, @"^\d{1,4}$")) ||
    (parts.Length == 2 && Regex.IsMatch(parts[0], @"^\d{1,4}$")) && 
        Regex.IsMatch(parts[1], @"^[0-9X]$"))
{

}

-- EDIT --

I can't tell if you want 0 or not, so if you don't, change \d from to [1-9].

answered Jul 24, 2018 at 10:48

Hambone

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Comments

Andrew Morton · Accepted Answer · 2018-07-24 11:03:40Z

It would be easier to have two tests: one to check if it could be valid, followed by one to exclude the special case of all leading zeros being invalid:

static void Main(string[] args)
{
    string[] agencias = { "", "1234-5", "0-9", "014777417", "0000", "1-23", "01-0", "1-234 abcd", "0123-4" };

    var regexAgenciaValid = new Regex("^(([0-9]{1,4})(-[0-9])?)$");
    var regexAgenciaInvalid = new Regex("^((0{1,4})(-[0-9])?)$");

    foreach (string agencia in agencias)
    {
        var result = regexAgenciaValid.IsMatch(agencia) && !regexAgenciaInvalid.IsMatch(agencia);
        Console.WriteLine(agencia + " " + result);
    }

    Console.ReadLine();

}

Output:

 False
1234-5 True
0-9 False
014777417 False
0000 False
1-23 False
01-0 True
1-234 abcd False
0123-4 True

This has the bonus of being easier to modify in the future.

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