If you want the index of the array, then either use the C-style for loop:

for (my $i = 0; $i <= $#array; $i++) {
  # index is in $i
  # element is in $array[$i];
}
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Or iterate over the indexes rather than the elements:

foreach (0 .. $#array) {
  # index is in $_
  # element is in $array[$_];
}
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Update: Changed $i to $_ in comments in the second code example. Thanks to arkturuz for spotting the error.