You're passing an array reference into the display() function, but within that function, you're not extracting things properly.

You can either do this:

display(@data);
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...then change your for loop in the function:

for my $dir (@dirs){ # idiomatic perl way to loop over a list
    print "$dir\n";
}
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If you want to stay with the reference, you must change how you extract the parameter(s), and then dereference the array reference when using it:

sub display {

    # pull out the aref passed in

    my $dirs = shift; # could also be `my ($dirs) = @_;`

    # loop over the aref. Note the syntax
    # could also be written with the circumfix operator:
    # @{ $dirs }

    for my $dir (@$dirs){
        print "$dir\n";
    }
}
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