splice can be used to add elements to an array.
@array = qw(1 2 4 5);
splice(@array,2,0,3);
print "$_\n" for @array;
In the above code:
2 - is the place in the array you are splicing (its the index value, not the element value)
0 - is the number of elements in the array to replace (we are not replacing any, only adding to the array, so use 0)
3 - is the replacement list (just one element in this case).