Did you test what is in your array?

Push just adds the values in the second array to the end of the first array. What you have is a flattened list rather than an array of arrays.

If you want to add a reference to an array you need to push(@mainarr,\@arr1);
Then you can access the second element of each using

for $array_ref (@mainarr){
   print "$array_ref->[1]\n";
}
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For further info have a look at perldoc perllol