Identify a string containing a single period with regex

user_17003758 0
Viewed 66

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.

ip hyperlink regex c#
2 Answers

Since you are coding in C#, it makes sense to use a non-regex approach here (see Klaus Gütter's comment):

var ContainsOnlyOneDot = text.Count(c => c == '.') == 1;

If you have to do that with a regex, 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.");
}
user_38329700

What about something like this?

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

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

user_169537390
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