re = /^(?:(“(?! “).*?)\s*”|(“) “(.*)|((?!“).*?)\s*”)$/m
str = '“ Criteria 1, ending with RD and beginning with LD, but not LDLD, remove RD ”
“ “ Criteria 1, ending with RD but beginning with LDLD, do nothing to RD ”
“ “ Criteria 2, beginning with LDLD, make it begin with LD ”
Criteria 3 with non-matching RD, remove RD ”'
subst = '$1$2$3$4'
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html