Exactly? The array contains 1001, 1002, 1003? Or the array has indexes 1001, 1002, 1003?

For example:

use strict;
use warnings;
use List::MoreUtils qw/firstidx/;

@array = qw/ fred tom jenny jeff claire /;
$array[3] = undef;
my $available_index = firstidx { not defined $_ } @array; 
$array[$available_index] = 'peter';
print "@array\n";
__END__
fred tom jenny peter claire
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