C# Regex to allow only alpha numeric

Question

I have the following regex ^[a-zA-Z0-9]+$ which would allow alpha numeric characters. The problem here is that if I enter only numeric character like \"897687\"

Answer 1

Or slightly less verbose than the accepted answer:

^[a-zA-Z][\w]*$

C# regex has character class indicator "\w" for alphanumeric characters, but does not have a character class for just alphabetic (no digits), hence you have to specify class set [a-zA-Z] manually.

Answer 2

Sounds like you want:

^[a-zA-Z][a-zA-Z0-9]*$

EXPLANATION

^ asserts position at the start of a line

Match a single character present in the list below [a-zA-Z]

» a-z a single character in the range between a (index 97) and z (index 122) (case sensitive)

» A-Z a single character in the range between A (index 65) and Z (index 90) (case sensitive)

Match a single character present in the list below [a-zA-Z0-9]*

* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)

a-z a single character in the range between a (index 97) and z (index 122) (case sensitive)

A-Z a single character in the range between A (index 65) and Z (index 90) (case sensitive)

0-9 a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)

$ asserts position at the end of a line

Demo

Answer 3

^[a-zA-Z][a-zA-Z0-9]*$

Should do the trick!

Alternatively, if you wish to include all alphanumeric plus an underscore you can use:

^[a-zA-Z][\w]*$

Answer 4

This is the best solution to check alphanumeric,

• if it is only string - "Error".
• if it is only integer - "Error".

• if it is alphanumeric -"Success".

  if (System.Text.RegularExpressions.Regex.IsMatch(txt.Text, @"[a-zA-Z]") && 
      System.Text.RegularExpressions.Regex.IsMatch(txt.Text, @"[0-9]")      
  {
      // Success - It is alphanumric
  }
  else   
  {
      // Error - It is not alphanumric
  }
  

Answer 5

Just in case that the ASCII characters are at some point not enough, here the Unicode version:

^\p{L}[\p{L}\p{N}]*$

\p{L} is any Unicode code point that has the property letter ==> Any letter from any language (that is in Unicode)

\p{N} is any Unicode code point that has the property number ==> Any number character from any language (that is in Unicode)

Answer 6

This function will return true or false based on whether the Regular Expression is matched or not,

   public static Boolean isAlphaNumeric(string strToCheck)
    {
        Regex rg = new Regex(@"^[a-zA-Z0-9\s,]*$");
        return rg.IsMatch(strToCheck);
    }