From: John Joyce <dangerwillrobinsondanger@...>
Date: 2007-04-21T09:16:01+09:00
Subject: Re: Finding non-printable characters using Regular Expressions

THE book on RegEx is "Mastering Regular Expressions" from OReilly.
It is a bit Perl focused in the examples, but the book itself is all  
about regular expressions in use.

On Apr 21, 2007, at 7:55 AM, Michael W. Ryder wrote:

> Alex Young wrote:
>> Michael W. Ryder wrote:
>>> Alex Young wrote:
>>>> Michael W. Ryder wrote:
>>>>> As part of a method I am playing with while learning Ruby I  
>>>>> need to be able to determine which characters in a string are  
>>>>> non-printable.  What is the "best" method for determining if a  
>>>>> character is printable, such as an "A", or unprintable, such as  
>>>>> a tab?
>>>>> While I could create a list of printable characters using  
>>>>> ranges is this the best way to do this?
>>>>>
>>>> The POSIX character classes are for exactly this:
>>>>
>>>> irb(main):001:0> "A \n B \t C".gsub(/[[:graph:]]/, '')
>>>> => " \n  \t "
>>>> irb(main):002:0> "A \n B \t C".gsub(/[[:print:]]/, '')
>>>> => "\n\t"
>>>>
>>>
>>> This is very close to what I am looking for.  If I use
>>> "A \n B \t C".gsub(/[^[:graph:]]/, '')
>>> it returns "ABC", but I need to keep the spaces and have not been  
>>> able to figure out how to include them in the output so that it  
>>> shows "A B C".
>>> Thank you for your assistance, it has given me a starting point  
>>> and I will have to spend some time experimenting and researching  
>>> to reach the final step.
>> You're nearly there.  Look a little closer at my suggestion,  
>> particularly the second regex.
>
> Thank you very much for your assistance using "A \n B \t C".gsub(/[^ 
> [:print:]]/, '') gives me "A B C" which is what I was looking for.
> Can you recommend a good reference on regular expressions so I can  
> learn more?
>