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From: Eric Bednarz <bednarz@fahr-zur-hoelle.org>
Newsgroups: comp.lang.javascript
Subject: Re: ScreenName validation
Organization: Eric Conspiracy Secret Labs
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Date: Fri, 11 Jan 2013 23:23:15 +0100
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Stefan Weiss <krewecherl@gmail.com> writes:

> Could you give an example of when the literal ] character doesn't have
> to be escaped in a character class?

I'm not sure what you are asking. Examples in other languages?

$ php -r 'echo preg_match("/^[]]$/", "]"), "\n";'
1

$ irb
>> /^[]]$/ =~ "]"
(irb):1: warning: character class has `]' without escape
=> 0

$ python
[...]
>>> import re
>>> re.compile('^[]]$').match(']')
<_sre.SRE_Match object at 0x109e39168>

$ groovysh
[...]
groovy:000> "]" ==~ /^[]]$/
===> true

> The empty character class is supported in many (but not all) PCRE-like
> regex implementations.

$ perl -e 'print "]" =~ /^[]]$/, "\n";'
1

> In addition to "\", "]", and "-", some languages also require the regex
> delimiter to be escaped in regex literals.

Well, some languages require you to .NOT escape the underscore. :-)