This also works, and doesn't require duplicating parameters passed to print / printf:

use strict;
use warnings;

my $a = chr(65);
my $b = chr(66);
my $c = chr(67);
printf ('%1$s'x2 . '%2$s'x3 . '%3$s'x4, $a, $b, $c);
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The %number$ modifier allows you to use a specific parameter passed to printf (see sprintf for more details), so we create a format string that prints the 1st parameter 2 times, the second parameter 3 times and the 3rd parameter 4 times, or '%1$s%1$s%2$s%2$s%2$s%3$s%3$s%3$s%3$s' though bear in mind if you use an interpolating string ("..." or qq{...}) you would likely need to escape the $ to \$