August 2012
Intermediate to advanced
609 pages
19h 16m
English
Content preview from Regular Expressions Cookbook, 2nd Edition
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8.15. Validating Domain Names
Problem
You want to check whether a string looks like it may be a valid, fully qualified domain name, or find such domain names in longer text.
Solution
Check whether a string looks like a valid domain name:
^([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}$| Regex options: Case insensitive |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python |
\A([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}\Z| Regex options: Case insensitive |
| Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby |
Find valid domain names in longer text:
\b([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}\b| Regex options: Case insensitive |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Check whether each part of the domain is not longer than 63 characters:
\b((?=[a-z0-9-]{1,63}\.)[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b| Regex options: Case insensitive |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Allow internationalized domain names using the punycode notation:
\b((xn--)?[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}\b| Regex options: Case insensitive |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Check whether each part of the domain is not longer than 63 characters, and allow internationalized domain names using the punycode notation:
\b((?=[a-z0-9-]{1,63}\.)(xn--)?[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b| Regex options: Case insensitive |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Discussion
A domain name has the form of domain.tld, or subdomain.domain.tld, or any number of additional subdomains. ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.