From: timsuth@... (Tim Sutherland)
Date: 2002-07-13T16:39:25+09:00
Subject: Re: gsub() replacement containing replaced text

In article <200207131507.17758.harryo@zip.com.au>, Harry Ohlsen wrote:
>This feels like a terribly newbie question to be asking, but I'm stymied ...
>
>I want to replace all single quotes in a string with backslask followed by a 
>single quote.  The obvious approach doesn't seem to work, presumably because 
>the replacement contains the pattern that's been replaced.
>
>I assume there's an easy way to do this, but can't for the life of me think 
>how.  Here's an example of the problem ...
>
>irb(main):001:0> x="Don't say goodbye"
>"Don't say goodbye"
>irb(main):002:0> x
>"Don't say goodbye"
>irb(main):003:0> x.gsub("'", "\\'")
>"Dont say goodbyet say goodbye"
>irb(main):004:0>

This issue is mentioned in 'Programming Ruby', "Standard Types" chapter (see
http://www.rubycentral.com/book/).

The problem is that you can use \&, \1 \2 etc. in the replacement string to
match groups, so gsub is gobbling up your \\.

The solution is to either do
	x.gsub("'", "\\\\'")
or
	x.gsub("'") { "\\'" }

The latter form works because when given a block, groups are given as
arguments to the block instead of using \1, \2 etc, so gsub doesn't have to
touch \'s in the replacement string.

-- 
int main(){int l=0,$=0;char _[8]="To:";while(l-3?(_[l]=$++["#u,UTGK gpFyLY "
#define p(r)p%:%:r("\45\56\52\163",(l=_[3])|7<:_:>%$,crypt(_,_+4%$)|_[6]%$);
"7&nvXD(AqEhsZA`Oh@in #oI.ZX #pXXhe"]):l)++l%8||p(rintf)sorry:gnu_crypt_only:}