From: Matthew Smillie <M.B.Smillie@...>
Date: 2006-06-29T02:12:15+09:00
Subject: Re: remove all illegal chars form string

On Jun 28, 2006, at 14:09, thomas coopman wrote:

> Hi,
>
> Is there a simple way to remove all but the legal chars from a  
> string.  where the legal chars are for example: a-z A-Z 0-9
> So everything should be removed from the string but these characters.
> "exam@p  Le3|�" --> "exampLe"
>
> I don't know very much about regular expressions, so I don't know  
> if it's possible with sub or gsub.  My first Idea was to loop over  
> the string and check every character but I wondered if there is  
> something more simple or better.
>
> Thanks

It's dead easy:

test = "exam@p  Le3|�"
test.gsub(/[^A-Za-z0-9]/, '')
=> "exampLe3"

Quick explanation:

[] defines a group you want to treat as one character.  If you only  
wanted vowels, ferinstance, you'd use [aeiou].

^ as the first character in a group means the opposite of that  
group.  Everything that isn't a vowel would be like this: [^aeiou]

A-Z is a range of characters, and you can do smaller ranges like c-q  
or whatever, the ordering used to determine the range is the  
character encoding.  This means you can just say A-z in place of A-Za- 
z (at least in ASCII and compatible encodings - I don't know about  
anything else), but I think that tends to make things a little less  
clear, especially since a-Z is invalid because a > Z in ASCII.

There are also shortcuts for some classes of characters, \d is  
equivalent to [0-9], and \w is close to [A-z0-9] but also includes  
the underscore character '_'.

So the regular expression says 'match any single character that is  
not in the ranges A-Z, a-z, or 0-9'.  #gsub takes everything matched  
by the regular expression, and replaces it with nothing.

matthew smillie.