Regular Expressions Cookbook

Chapter 7. URLs, Paths, and Internet Addresses

Along with numbers, which were the subject of the previous chapter, another major subject that concerns a wide range of programs is the various paths and locators for finding data:

• URLs, URNs, and related strings

• Domain names

• IP addresses

• Microsoft Windows file and folder names

The URL format in particular has proven so flexible and useful that it has been adopted for a wide range of resources that have nothing to do with the World Wide Web. The toolbox of parsing regular expressions in this chapter will thus prove valuable in a surprising variety of situations.

7.1. 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 ...