From: Eric Armstrong <Eric.Armstrong@...>
Date: 2006-07-29T08:30:16+09:00
Subject: Re: Finding "\" in a string

Omigawd. I'm more confused than ever! But
I have some great patterns to follow until
the day of my enlightenment arrives!

Thanks guys. I look forward to the day this
all makes sense...
:_)

Logan Capaldo wrote:
> 
> On Jul 28, 2006, at 7:10 PM, Paul Battley wrote:
> 
>> On 28/07/06, Eric Armstrong <Eric.Armstrong@sun.com> wrote:
>>> Very helpful. At least now I have a good idea that it
>>> can be made to work. Now let's see if I can dial in my
>>> understanding with respect to replacement strings...
>>>
>>> The fact that \1, \2 are recognized /shouldn't/ matter,
>>> because the tokenizer really ought to ignore any \x
>>> sequence where the x isn't a known special character.
>>> But it's rapidly becoming apparent that the tokenizer
>>> takes any \x and translates it to /something/, so we
>>> need \\ to get one \ in the string.
>>
>> In fact, the tokenizer *does* ignore non-special sequences:
>>
>> "\\foo".gsub("\\", "\\x") # => "\\xfoo"
>>
>> And if there's nothing else left in the string, that works, too:
>>
>> "\\foo".gsub("\\", "\\") # => "\\foo"
>>
>> However, in order to be able to produce a literal \1, it also needs to
>> understand \\. Therefore, this gives the same effect:
>>
>> "\\foo".gsub("\\", "\\\\") # => "\\foo"
>>
>> But I missed a trick earler. We only actually need six backslashes to
>> emit two: the end of the string will terminate the sequence as in the
>> second example:
>>
>> "\\foo".gsub("\\", "\\\\\\") # => "\\\\foo"
>>
>> Is it getting clearer?
>>
>> Paul.
>>
> 
> This is why when I need to gsub backslashes I use a block:
> 
> gsub(%r{\}) { '\\' }
> 
> 
>