[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.ruby

gsub and backslashes

John Wright

1/21/2007 3:25:00 PM

Say I want to replace all occurrences of \ in a string with \\:

test = "a string with \\ a backslash"
puts test.gsub(/\\/, "\\\\") #no worky
=> a string with \ a backslash

puts test.gsub(/\\/, "\\\\\\") #why does this work?
=> a string with \\ a backslash

Why does the replacement string have to be six backslashes? Hopefully
this is really simple and I'm just being dense...

--
Posted via http://www.ruby-....
4 Answers

WoNáDo

1/21/2007 3:36:00 PM

0

John Wright schrieb:
> Say I want to replace all occurrences of \ in a string with \\:
>
> test = "a string with \\ a backslash"
> puts test.gsub(/\\/, "\\\\") #no worky
> => a string with \ a backslash
>
> puts test.gsub(/\\/, "\\\\\\") #why does this work?
> => a string with \\ a backslash
>
> Why does the replacement string have to be six backslashes? Hopefully
> this is really simple and I'm just being dense...
>

Ooops

irb(main):005:0> puts "a string with \\ a backslash".gsub(/\\/, "\\\\\\\\")
a string with \\ a backslash

This works as expected, but why it works with '\'*6 I don't understand.

Wolfgang Nádasi-Donner

Gavin Kistner

1/21/2007 3:40:00 PM

0

John Wright wrote:
> Say I want to replace all occurrences of \ in a string with \\:

This is a FAQ. Please search the mailing list archives and the web;
there have been numerous discussions of it, articles written about it,
and it's addressed in the free online version of Programming Ruby.

Definitely come back with more questions if you really can't find the
answer online, though.

WoNáDo

1/21/2007 4:46:00 PM

0

Wolfgang Nádasi-Donner schrieb:
> Ooops
>
> irb(main):005:0> puts "a string with \\ a backslash".gsub(/\\/, "\\\\\\\\")
> a string with \\ a backslash
>
> This works as expected, but why it works with '\'*6 I don't understand.

Even after looking to "Programming Ruby - Second Edition", and several other
places, I have no idea why it works with '\\\\\\', and other strange things like
this:

irb(main):001:0> x = "a\\b"
=> "a\\b"
irb(main):002:0> puts x
a\b
=> nil
irb(main):003:0> puts x.gsub(/\\/, '+\\\\\\+')
a+\b
=> nil
irb(main):004:0> puts x.gsub(/\\/, '+\\\\\\\\+')
a+\\+b
=> nil
irb(main):005:0> puts x.gsub(/\\/, '+\\\\\\t')
a+\\tb
=> nil
irb(main):006:0> puts x.gsub(/\\/, '+\\\\\\\\t')
a+\\tb
=> nil

Especially if I take the following into account:

irb(main):001:0> x = '\\\\'
=> "\\\\"
irb(main):002:0> puts x
\=> nil
irb(main):003:0> puts Regexp.escape(x)
\\\=> nil
irb(main):004:0> Regexp.escape(x) == '\\\\\\\\'
=> true
irb(main):005:0> Regexp.escape(x) == '\\\\\\'
=> false

Wolfgang Nádasi-Donner

William James

1/21/2007 8:02:00 PM

0


John Wright wrote:
> Say I want to replace all occurrences of \ in a string with \\:
>
> test = "a string with \\ a backslash"
> puts test.gsub(/\\/, "\\\\") #no worky
> => a string with \ a backslash
>
> puts test.gsub(/\\/, "\\\\\\") #why does this work?
> => a string with \\ a backslash
>
> Why does the replacement string have to be six backslashes? Hopefully
> this is really simple and I'm just being dense...

puts test.gsub(/\\/, '\&\&')