Seemingly easy RegEx giving me problems [duplicate]-CodePudding

Well, the Title pretty much explains my question, but in addition; I am coding in C# for the first time and have limited development experience overall (I am a tester typically)

Mods: I had a look to see if there were any rules about posting a question simply asking for help with a RegEx and could not find anything specific. I attempted to utilize several online regex "generators" but it seems you need to be fairly fluent in order to take advantage of any on offer. I know there are users on here that are absolutely gifted when it comes to formulating strong regular expressions - so here I am posting what seems like a dopey question. Apologies if Ive overlooked something in my frustration.

To all who answer, or attempt to answer - thank you kindly for your time.

Relevant Info:

I am using this Regex to validate textbox input
The expression may contain between 1 & 8 alphanumeric characters (including underscores and hyphens), but nothing else.
Some examples of valid input are "alpha_01", "1234-567", "1337", "A", "123_AbC"
Examples of invalid input are "$cash", "<test>", "this.one"
I wish for the text box content to display red in color if the entry is invalid and black if valid.
I have tried a multitude of expressions that successfully validate in the manner I desire, however all the expressions I have tried also validate undesired characters.
Expressions I have tried are (@([[:alnum:]]{1,8})) (@([\w]{1,8})) & ((@[a-zA-Z0-9_-]{1,8}))
If I were to limit the text box to 8 characters and use a Regex to disallow entry of undesired characters, I imagine that might suffice for my purposes, but I am not fluent enough in regex to write an expression limiting input in the manner needed.

I doubt it adds anything relevant, but for context here is my current code snippet;

     private void textBox1_TextChanged(object sender, EventArgs e)
     {       
            if ((new Regex(**REGEX NEEDEED**).IsMatch(textBox1.Text)))
            {
                textBox1.ForeColor = Color.Black;
            } 
            else 
            {
                textBox1.ForeColor = Color.Red;
            }
     }

CodePudding user response：

Does this RegEx work for you?

^[a-zA-Z0-9\-_]{1,8}$

This code:

var inputs = new[] { "alpha_01", "1234-567", "1337", "A", "123_AbC", "$cash", "<test>", "this.one", "muchtoolong" };

var regex = new Regex(@"^[a-zA-Z0-9\-_]{1,8}$");

foreach(var input in inputs)
{
    var isMatch = regex.IsMatch(input);
    Console.WriteLine(input   " "   isMatch.ToString());
}

Gives:

alpha_01 True

1234-567 True

1337 True

A True

123_AbC True

$cash False

<test> False

this.one False

muchtoolong False