When looking at line 9 in your source code, there is a string eq test. That warning warns you that you are using a value ($need[$incr]) in a string equality test (eq '') and that value is undefined. Maybe you are confused how to iterate over an array. for(;;) is not the way to iterate over an array. And while all elements of an array after its defined length will be equal to the empty string, that will produce the warning, as all accesses to an array outside its defined length return undef. If you are doing array manipulation, you want to read foreach and push.

Your loop can be written even shorter by using grep:

my @array1 = grep { /^sanj/ } @need;
[download]