There is not. If you're reading a file $. contains the file's line number. But if you're iterating over elements in an array it may make sense in some situations to iterate over the index instead:

foreach my $idx ( 0 .. $#array ) {
    do_something($array[$idx]) unless $idx % 3;
    # Do something else that isn't filtered by iteration number.
}
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In your example, it's probably clearer to iterate over the list rather than the indices, but in some cases the code becomes clearer the other way.