.abc(pqr)

.abc(abc_p)

##</code><code>##

.abc(pqr)

.abc_1(abc_p_1)

.abc_2(abc_p_2)

##</code><code>##

my $a    =  qr{ [ .(] }xms;
my $b    =  qr{  abc | abc_p  }xms;

while (my $line = <$fh>) {

if ($line =~ m{ $a $b }xms) {
        for my $i (1 .. 2) {
            (my $c = $line) =~ s{ ($a $b) }{${1}_$i}xmsg;
            print $out $c;
            }
        }
}
 else {
          
        print $out $line;
        }

    }