解析字符串中的多个主机名

Question

I am trying to parse multiple hostnames from a string using a Regex in C#.

Example string: abc.google.com another example here abc.microsoft.com and another example abc.bbc.co.uk

The code I have been trying is below:

string input = "abc.google.com another example here abc.microsoft.com and another example abc.bbc.co.uk";
string FQDN_Pat = @"^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])(\.([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}[a-zA-Z0-9]))*$";

Regex r = new Regex(FQDN_Pat);
Match m = r.Match(input);         
while (m.Success)
{
    txtBoxOut.Text += "Match: " + m.Value + " ";
    m = m.NextMatch();
}

The code works if the string fits the pattern exactly eg abc.google.com .

How can I change the Regex to match the patterns that fit within the example string eg so the output would be:

Match: abc.google.com
Match: abc.microsoft.com
Match: abc.bbc.co.uk

Apologies in advance if this is something very simple as my knowledge of regular expressions is not great! :) Thanks!

UPDATE:

Updating the Regex to the following (removing the ^ and $ ):

string FQDN_Pat = @"([a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?)(\.([a-zA-Z0-9]|[a-zA-Z0-9][a-zA‌​-Z0-9\-]{0,61}[a-zA-Z0-9]))"; 

Results in the following output:

Match 1: abc.g
Match 2: oogle.c
Match 3: abc.m
Match 4: icrosoft.c
Match 5: abc.b
Match 6: bc.c
Match 7: ou

Answer 1

As the regexp is quite complicated I tried to simplify it a bit. So what I've done was to

1. Remove ^ and $ to make the regexp match anywhere
2. Simplify characters that you match to , so instead of ([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\\-]{0,61}[a-zA-Z0-9]) i'm using ([a-zA-Z0-9])+ which means look for any alphanumeric sequence with length higher than one (the + sign means that you match to a char that appears once or more). Let's call it X . If the rules for names in FQDN are more complex please modify this value

3. Expression for finding FQDN is X(\\.X)+ . This can be viewed as sequence of chars followed by one or more sequences, all are separated by dots ( . ). Substitiuting X you have full expression given as

    string FQDN_Pat = @"([a-zA-Z0-9]+)(\\.([a-zA-Z0-9])+)+"; 

which actually matches to your example but I suggest you read C# regexp manuals for further references in case there are some tricks in domain names

Answer 2

You get this behavior because you are only matching the string that contain nothing else but your pattern. You are using ^ (start of the string) and $ (end of the string). If you want to match your pattern anywhere in the input string remove those characters from the pattern.