From: botp <botpena@...>
Date: 2010-11-21T18:57:45+09:00
Subject: Re: gsub and backslashes

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On Sun, Nov 21, 2010 at 6:13 AM, Ralph Shnelvar <ralphs@dos32.com> wrote:
> What I want is to change single backslashes to double backslashes.  The
result of the above substitution is "no change"
>
> On the other hand
>  "\\1\\2\\3".gsub(/\\/,"\\\\\\\\")
> does do what I want ... but I am clueless as to why.

there are many ways,

#1
"\\1\\2\\3".gsub(/(\\)/,"\\1\\1").scan /./
#=> ["\\", "\\", "1", "\\", "\\", "2", "\\", "\\", "3"]

#2
"\\1\\2\\3".gsub(/(\\)/,'\1\1').scan /./
#=> ["\\", "\\", "1", "\\", "\\", "2", "\\", "\\", "3"]

#3
"\\1\\2\\3".gsub(/\\/){"\\\\"}.scan /./
#=> ["\\", "\\", "1", "\\", "\\", "2", "\\", "\\", "3"]

#4
"\\1\\2\\3".gsub(/(\\)/){$1+$1}.scan /./
#=> ["\\", "\\", "1", "\\", "\\", "2", "\\", "\\", "3"]


#1 & #2 samples uses group backreferences, ruby may need second parsing pass
for this feature to work...

#3 & #4 uses code blocks. may not need second pass. backreferences can be
had using $n notation.

best regards -botp

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