From: Paul Rubel <prubel@...>
Date: 2004-11-04T03:12:06+09:00
Subject: escaping single quotes in a string with gsub

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.

This has a problem when there is an escaped slash before the quote:
\\'. I believe the fix should be to look two characters back. If
anyone has a canned solution I'm all ears. Would look-behind be an
option here out of the box?

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}\\\\'*"))
  puts $1
end
#end
\'Summe*\'*s Day
r
\'Summe*r\'*s Day
r
prubel /tmp> ruby --version
ruby 1.8.1 (2004-02-06) [i686-linux-gnu]


I'm confused at to why the output is different for the two
iterations? Why doesn't the r get placed in the first output?


         thank you for your help,
             Paul