Well, if you're sure that the result is being overwritten, then you have probably declared the array within the foreach loop:

my @array = (1,2,3,4,5);
foreach my $line (@array) {
  my @newarray;
  push (@newarray, $line);
  print @newarray;
}
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To prevent overwriting you should declare the new array outside the loop:

my @array = (1,2,3,4,5);
my @newarray;

foreach my $line (@array) {
  push (@newarray, $line);
}

print @newarray;
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Of course, you could be doing something entirely different - so difficult to know without seeing the code...