Identify a string containing a single period with regex-CodePudding

I am trying to write a regex operation that will simply identify if there is only one period within a string.

For example, it will recognize arandomlink.online and a@second#random-link.fr, but it will not recognize an IPV4 IP Address with multiple periods, like 5.6.7.8.

I'm currently using:

string URLpattern = @"\w*\.\w";

but the code above identifies IP addresses, which I don't want.

Anybody have any ideas? It's probably a very simple equation, but it's not coming to me right now. I can't figure out how to limit the equation to only identifying one period within the string, and not multiple. Because I'm working with Hash's and other things, it's best if I identify the URL's with the single period.

CodePudding user response：

You can use

^[^.]*\.[^.]*$

See the regex demo. Details:

^ - start of string
[^.]* - zero or more chars other than .
\. - a dot
[^.]* - zero or more chars other than a . char
$ - end of string.

In C#, you can use

if (Regex.IsMatch(text, @"^[^.]*\.[^.]*$"))
{
    Console.WriteLine("The string contains one dot only.");
}
else
{
    Console.WriteLine("The string contains no dots or more than one dot.");
}

CodePudding user response：

What about something like this?

[^\s\.] \.{1}[^\s\.]

So one dot surrounded with negating sets of anything except a dot and a whitespace.