Thanks Rob, that's exactly what I was missing -- the second round of
escaping is necessary to make escaped references to regex groups work.


-----Original Message-----
From: Rob Biedenharn
Sent: 02/22/2008 09:48 AM
> On Feb 22, 2008, at 12:27 PM, John Woods wrote:
>> The following confusing behavior is noted in the pickaxe book (2nd ed)
>> on page 75:
>>
>> # I would expect two backslashes in the result
>> irb> puts "\\".gsub("\\","\\\\")
>> \
>>
>> # I would expect four backslashes in the result
>> irb> puts "\\".gsub("\\","\\\\\\\\")
>> \\
>>
>> I can certainly work around it, but it seems unintuitive. Is there a
>> reason why gsub behaves this way? Just curious...
>
>
> Notwithstanding the earlier responses...
>
> Since the replacement string is evaluated 'twice', once as a ruby string
> literal and then again by gsub to look for group refrences like '\1',
> you need to provide two levels of escaping for a backslash.
>
> \ is "\\"
> so two of them is "\\\\"
> and you want gsub to see that so it need to have them escaped: "\\\\\\\\"
>
> Whew! Yeah, it's unfortunate, but backslash is doing double-duty here:
> introducing a group reference to the regular expression and escaping
> characters in a string literal (just like "\n", but also itself).
>
> -Rob
>
> Rob Biedenharn http://agileconsultingllc.com
> Rob@AgileConsultingLLC.com
>
>
>