From: Paul Rubel <prubel@...>
Date: 2004-11-04T05:08:59+09:00
Subject: Re: escaping single quotes in a string with gsub



James Edward Gray II writes:
 > On Nov 3, 2004, at 12:12 PM, Paul Rubel wrote:
 > 
 > > Hi,
 > >
 > > I'm trying to take a string and escape a single quote if it is not
 > > already escaped. My first thought was to look at the string and if I
 > > see a quote without a backslash before it put the backslash there.
 > 
 > What about:
 > 
 > gsub(/(\\*)'/) { |m| $1.length % 2 == 0 ? $1 + "\\'" : m }

That does look much better.

 > > While I was experimenting I saw some behavior I don't understand and
 > > am hoping someone can explain it to me:
 > >
 > > prubel@cornet /tmp> cat /tmp/t.rb ; ruby /tmp/t.rb
 > > 2.times do
 > >   # replace not a slash followed by a quote with not a slash
 > >   # and an escaped quote.
 > >   puts("\\'Summer's Day".gsub(/([^\\\\])'/,"*#{$1}\\\\'*"))
 > 
 > The above line is problematic for two reasons.  First, when using the 
 > replacement string version of gsub(), your string is interpolated 
 > before the method is even called let alone before any matches are made 
 > so $1 and friends are not set.  Instead, try using a \1 in a single 
 > quoted string or \\1 in a double to get the value you're after.

I should have know. Thanks for the explanation. 

 > Two, I don't understand your pattern.  [^\\\\] means ONE character that 
 > is not a slash and also not a slash.  It's identical to [^\\].  I think 
 > you meant to say, not two slashes, but that's a little harder to 
 > express in a regex.  And what if there are three slashes?  See my 
 > solution above for a different approach.

I mean to say not a slash but the interpolation in the replacement
confused me. After reading your response and thinking a bit I believe
my head has been wrapped around the issue. 


 > Hope that helps.

Very much.
      thank you,
        Paul