use strict;
my $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 ”';
my $regex = qr/^(?:(“(?! “).*?)\s*”|(“) “(.*)|((?!“).*?)\s*”)$/mp;
my $subst = '$1$2$3$4';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
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 Perl, please visit: http://perldoc.perl.org/perlre.html