## Problem

You want to check whether a string represents a valid IPv6 address using the standard, compact, and/or mixed notations.

## Solution

### Standard notation

Match an IPv6 address in standard notation, which consists of eight 16-bit words using hexadecimal notation, delimited by colons (e.g.: `1762:0:0:0:0:B03:1:AF18`). Leading zeros are optional.

Check whether the whole subject text is an IPv6 address using standard notation:

`^(?:[A-F0-9]{1,4}:){7}[A-F0-9]{1,4}\$`
 Regex options: Case insensitive Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python
`\A(?:[A-F0-9]{1,4}:){7}[A-F0-9]{1,4}\Z`
 Regex options: Case insensitive Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby

Find an IPv6 address using standard notation within a larger collection of text:

`(?<![:.\w])(?:[A-F0-9]{1,4}:){7}[A-F0-9]{1,4}(?![:.\w])`
 Regex options: Case insensitive Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby 1.9

JavaScript and Ruby 1.8 don’t support lookbehind. We have to remove the check at the start of the regex that keeps it from finding IPv6 addresses within longer sequences of hexadecimal digits and colons. A word boundary performs part of the test:

`\b(?:[A-F0-9]{1,4}:){7}[A-F0-9]{1,4}\b`
 Regex options: Case insensitive Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

### Mixed notation

Match an IPv6 address in mixed notation, which consists of six 16-bit words using hexadecimal notation, followed by four bytes using decimal notation. The words are delimited with colons, and the ...

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