Regular Expression Forward Slash

Prashanti Rao

Hi!

I have been having some problems with regular expressions. I want to validate user input when a bus number is entered.

Examples: 37, 37A, 37S, 37A/L, 16A/250, 16A/250K etc

The regular expression I came up with is

(^\d{1,3}[A-Z]{0,3})|(^[\d{1,3}[A-Z]{0,3}\/\d{0,3}[A-Z]{0,3}])

It validates 37, 37A, 37S but when it comes to validating 37A/L it fails. Can someone tell me where I am going wrong with this?

P.S I am using a regular expression validator for a text box. I have placed this in the ValidationExpression.

Thanks.
Prashanti.

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Prashanti Rao13y ago
Thank you Vulpes. Your suggestion about the placement of parentheses and square brackets was really helpful.
Prashanti Rao13y ago
Solved It!!
The correct answer was
(^\d{1,3}[A-Z]{0,3}$)|(^\d{1,3}[A-Z]{0,3}\/\d{0,3}[A-Z]{0,3}$)

It was having problem as end of string was not specified.
Vulpes13y ago
Well, although it looks like it might be, forward slash is not actually a regular expression meta-character and so doesn't need escaping.

However, the real problem is that the placement of your parentheses and square brackets isn't quite right.

The following is working OK for me:

using System;
using System.Text.RegularExpressions;

class Test
{
static void Main()
{
string[] buses = {"37", "37A", "37S", "37A/L", "16A/250", "16A/250K", "A6"};
string regExp = @"(^\d{1,3}[A-Z]{0,3}|^\d{1,3}[A-Z]{0,3}/\d{0,3}[A-Z]{0,3})";
foreach(string bus in buses)
{
Console.WriteLine(Regex.IsMatch(bus, regExp));
}
Console.ReadKey();
}
}

The output is:

True
True
True
True
True
True
False