From: Brian Candler <b.candler@...>
Date: 2009-05-12T16:37:42+09:00
Subject: Re: question to write \4 into file

Cheyne Li wrote:
> Thanks. After puting 8 slashes, the path is correctely written in the 
> file...speachless...

Then there is something else which is doing a third level of dequoting. 
I can't say what this is, since you don't show your code.

Perhaps you are passing the string to a shell, e.g. using backticks, 
%x{...}, system(), IO.popen or similar. In this case, the shell also 
treats backslash sequences specially.

irb(main):001:0> str = "\\\\"
=> "\\\\"
irb(main):002:0> puts str
\\
=> nil
irb(main):003:0> system("echo #{str}")
\
=> true

Here, str is actually two characters (backslash followed by backslash). 
But the shell treats this as a single backslash-escaped character.

You can avoid this problem by not getting the shell involved. If you 
pass multiple arguments to system() then it invokes the target program 
with the arguments exactly as given, without invoking the shell at all.

irb(main):004:0> system("echo", str)
\\
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