From: Brian Candler <b.candler@...>
Date: 2009-05-12T05:25:56+09:00
Subject: Re: question to write \4 into file

Cheyne Li wrote:
> Hi there,
> 
> I have problem with writng "\4" into a file, for example, I want to
> write a string "aaa\4024_folder\mm" into a file test.cfg. But once the
> string wrote into file, it is "aaa024_folder\mm".

That's because \4 inside a double-quoted string is a single character, 
with code 4.

If you want a backslash inside a double-quoted string, put two 
backslashes.

irb(main):001:0> str = "aaa\\4024_folder\\mm"
=> "aaa\\4024_folder\\mm"
irb(main):002:0> puts str
aaa\4024_folder\mm
=> nil

If you are building filenames, note that even under Windows you can use 
forward-slashes inside Ruby.

Inside a gsub replacement string it can be even more confusing, since a 
backslash followed by 4 means "replace this with the fourth capture in 
the match". So to replace x with \4, you need to do this

irb(main):003:0> str = "wxyz"
=> "wxyz"
irb(main):004:0> res = str.gsub(/x/, "\\\\4")
=> "w\\4yz"
irb(main):005:0> puts res
w\4yz
=> nil

Or use the block form of gsub, which doesn't treat backslash-N 
specially.

irb(main):007:0> res = str.gsub(/x/) { "\\4" }
=> "w\\4yz"
irb(main):008:0> puts res
w\4yz
=> nil
-- 
Posted via http://www.ruby-forum.com/.