use strict;
my $str = 'CN=(A) Gro up3,OU=OU-Path1,OU=OU-Path2,DC=domain,DC=local
CN=(A) Group1,OU=OU-Path1,OU=OU-Path2,DC=domain,DC=local
CN=(A) Gro\\,up4,OU=OU-Path1,OU=OU-Path2,DC=domain,DC=local
CN=(A) Group2,OU=OU-Path1,OU=OU-Path2,DC=domain,DC=local';
my $regex = qr/^CN=(.*?)(?<!\\),.*/mp;
my $subst = '$1';
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