my $line = "1,2,3";
my $ft_count = 0;

$ft_count++ while($line =~ m/[,]/g);

if ($ft_count == 2) {
    my $n = 2;
    my $r = $n - 1;

    $line =~ s/((?:,.*?){}),/${1}|/;   
}

say $line;