From: "Wolfgang Nádasi-Donner" <ed.odanow@...>
Date: 2009-03-07T21:00:34+09:00
Subject: [ruby-core:22719] Re: [Bug #1251] gsub problem

Yukihiro Matsumoto schrieb:
> To substitute one backslash into two, you have to do
> 
>   s.gsub!("\\","\\\\\\")
...
myprompt> irb191-p0
irb(main):001:0> puts "a\\b".gsub!("\\","\\\\\\")
a\\b
=> nil
irb(main):002:0> puts "a\\b".gsub!("\\","\\\\\\\\")
a\\b
=> nil

I was surprized by this result long ago, until I started to assume, that
the second replacement works only for \<...>, \nr, \\, and leaves the 
backslash as it is in all other combinations (even at end of the string).

This ist different from the first replacement, which consumes always a 
backslash as escape character...

myprompt> irb191-p0
irb(main):001:0> puts "\\\w"
\w
=> nil

I think this behaviour should be documented somewhere, because it can 
really confuse persons, which do not use complex RegExes during their 
daily work.

Wolfgang N�dasi-Donner