From: Eric Armstrong <Eric.Armstrong@...>
Date: 2006-07-29T06:50:24+09:00
Subject: Re: Finding "\" in a string

Arnaud Bergeron wrote:
> On 7/28/06, Eric Armstrong <Eric.Armstrong@sun.com> wrote:
>> I'm going crazy, right? Surely it is possible
>> to find a backslash (\) in a string, and
>> replace it with two backslashes. That's simple,
>> right? Just gsub("\\", '\\'). That's all there
>> is to it.
> 
> irb> puts '\\'
> \
> => nil
> 
> You are replacing single slashes with single slashes.
>
You would think so, wouldn't you? But note that
I've used single quotes for the replacement.
So it /should/ equate to two backslashes.

So I tried four of them in the replacement string.
I did so yesterday, in fact, and repeated the
experiment today:

   testpath = "\\foo\\bar"
   result = testpath.gsub("\\", '\\\\')
   p result      # => "\\foo\\bar" (s/b "\\\\foo\\\\bar"
   puts result   # => \foo\bar     (s/b \\foo\\bar)

Notice that the results are unchanged. So I tried a
simple character: testpath.gsub("\\", 'r')

That worked as expected:

   "\\foo\\bar"
   \foo\bar
   "rfoorbar"
   rfoorbar

So it would appear that something strange is happening
in the evaluation of the gsub replacement string.




>> Except that...
>>
>> #!/usr/bin/env ruby
>>
>> testpath = "\\foo\\bar"
>> p testpath    # => "\\foo\\bar"  --representation
>> puts testpath # => \foo\bar      --what you see
>>
>> result = testpath.gsub("\\", '\\')
>> p result      # => "\\foo\\bar"
>>    (represenation unchanged. Should be "\\\\foo\\\\bar")
>>
>> puts result   # => \foo\bar
>>    (unchanged. should be \\foo\\bar)
>>
>> I've tried lots of gsub variations, like
>>     /\\/, '\\', "\\\\", and anything else I could
>> think of that came even close to being sensible,
>> but I've yet to find anything that works.
>>
>> My workaround will be to add a sed script to
>> filter the input. But surely that isn't necessary.
>> Is it?
>>
> 
> 
>