From: Mike Stok <mike@...>
Date: 2012-05-20T22:42:17+09:00
Subject: [ruby-core:45153] Re: [ruby-trunk - Bug #6474][Open] Substitution bug in String # gsub

Maybe you are bing confused by the way irb displays results as double quoted strings.  If you explicitly use puts:

ratdog:~ mike$ irb
1.9.3-p125 :001 > s = 'a&b'
 => "a&b" 
1.9.3-p125 :002 > puts s.gsub '&', '\&'
a&b
 => nil 
1.9.3-p125 :003 > puts s.gsub '&', '\\&'
a&b
 => nil 
1.9.3-p125 :004 > puts s.gsub '&', '\\\&'
a\&b
 => nil 
1.9.3-p125 :005 > puts s.gsub '&', '\\\\&'
a\&b
 => nil 

I like using a block to make this situation less full of backslashes e.g.

1.9.3-p125 :006 > puts s.gsub('&') { '\&' }
a\&b

To see the way irb displays strings consider:

1.9.3-p125 :008 > s = 'a\&b'
 => "a\\&b" 
1.9.3-p125 :009 > puts s
a\&b
 => nil 
1.9.3-p125 :010 > puts s.length
4
 => nil 
1.9.3-p125 :011 > s = "a\tb"
 => "a\tb" 
1.9.3-p125 :012 > puts s
a	b
 => nil 

Hope this helps,

Mike

On 2012-05-20, at 9:19 AM, hadmut (Hadmut Danisch) wrote:

> 
> Issue #6474 has been reported by hadmut (Hadmut Danisch).
> 
> ----------------------------------------
> Bug #6474: Substitution bug in String # gsub
> https://bugs.ruby-lang.org/issues/6474
> 
> Author: hadmut (Hadmut Danisch)
> Status: Open
> Priority: Normal
> Assignee: 
> Category: 
> Target version: 
> ruby -v: ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-linux]
> 
> 
> Hi,
> 
> I need to replace all occurences of &  with \&  in a String (generating LaTeX input). 
> 
> However, gsub has a problem with unescaping the \ character in the replacement string:
> 
> irb(main):001:0> "a&b"
> => "a&b"
> irb(main):002:0> "a&b".gsub('&','\&')
> => "a&b"
> irb(main):003:0> "a&b".gsub('&','\\&')
> => "a&b"
> irb(main):004:0> "a&b".gsub('&','\\\&')
> => "a\\&b"
> irb(main):005:0> "a&b".gsub('&','\\\\&')
> => "a\\&b"
> 
> So it always inserts either zero or two \ characters, but never a single one. Not possible to generate "a\&b"
> 
> 
> regards
> 
> 
> 
> 
> -- 
> http://bugs.ruby-lang.org/

-- 

Mike Stok <mike@stok.ca>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.