This feels like more of a C task than a perl task, so here's an answer in C-like perl...

my @pos = (2,4,6,9);
my $bin = 0;
for (my $i = 0; $i < scalar @pos; $i++)
{
    $bin |= 1 << $pos[$i];
}
# Printing out the result is left as a follow-on exercise...
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