Regular Expressions Cookbook, 2nd Edition

8.1. Validating URLs

Problem

You want to check whether a given piece of text is a URL that is valid for your purposes.

Solution

Allow almost any URL:

^(https?|ftp|file)://.+$

Regex options: Case insensitive

Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python

\A(https?|ftp|file)://.+\Z

Regex options: Case insensitive

Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby

Require a domain name, and don’t allow a username or password:

\A                         # Anchor
(https?|ftp)://            # Scheme
[a-z0-9-]+(\.[a-z0-9-]+)+  # Domain
([/?].*)?                  # Path and/or parameters
\Z                         # Anchor

Regex options: Free-spacing, case insensitive

Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby

^(https?|ftp)://[a-z0-9-]+(\.[a-z0-9-]+)+↵
([/?].+)?$

Regex options: Case insensitive

Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Require a domain name, and don’t allow a username or password. Allow the scheme (http or ftp) to be omitted if it can be inferred from the subdomain (www or ftp):

\A                             # Anchor
((https?|ftp)://|(www|ftp)\.)  # Scheme or subdomain
[a-z0-9-]+(\.[a-z0-9-]+)+      # Domain
([/?].*)?                      # Path and/or parameters
\Z                             # Anchor

Regex options: Free-spacing, case insensitive

Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby

^((https?|ftp)://|(www|ftp)\.)[a-z0-9-]+(\.[a-z0-9-]+)+([/?].*)?$

Regex options: Case insensitive

Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python

Require a domain name and a path that points to an image file. Don’t allow a username, password, or parameters:

\A # Anchor (https?|ftp):// # Scheme [a-z0-9-]+(\.[a-z0-9-]+)+ ...