Regular expression to match IRC nickname

Question

How would I use a regular expression to match an IRC nickname? This is being done in Ruby if that makes a difference (it probably will, with the syntax of the regex, but who knows.)

EDIT: An IRC nickname can contain any letter, number, or any of the following characters: < - [ ] \ ^ { }

Answer 1

# If you are testing a single string
irc_nick_re = /\A[a-z_\-\[\]\\^{}|`][a-z0-9_\-\[\]\\^{}|`]*\z/i 

# If you are scanning them out of a larger string
irc_nick_re = /(?<=[^a-z_\-\[\]\\^{}|`])[a-z_\-\[\]\\^{}|`][a-z0-9_\-\[\]\\^{}|`]*/i 

The above allows single-character names. If two characters are required, change the * to +. If three characters (or more) are required, change it to {2,}, where '2' is the minimum number of characters minus 1.

If there is a maximum number of characters (for example, EFNet only allows nicknames up to 9 characters lone, while Freenode allows nicks up to 16 characters long) then you can include that number (minus 1) after the comma. For example:

# Validate nicknames that are between 3 and 16 characters long (inclusive)
irc_nick_re = /\A[a-z_\-\[\]\\^{}|`][a-z0-9_\-\[\]\\^{}|`]{2,15}\z/i