Use:

my   @foo;
push @foo, 5;
push @foo, 7, 8;

printf  "@foo\n";
printf  "\nabove first set of dashes #:  [$#foo]\n";
printf  "first set of dashes------------\n";
printf  "\nsecond set of dashes------------\n";

my $y = printf  "\ny dashes------------\n";
printf "\ny: [$y]\n";
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---------------------------------------------------------- As you are using (") double quotes the concatenation operator is not required , so we can ignore that.