Using a While loop, is it possible to read a file from the last line, and then up, rather than from the first line and down ?

So I have a data file like this:
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
17 18 19 20
21 22 23 24

I need to read this file and print it to another file in the format

21 22 23 24 17 18 19 20 13 14 15 16

with the specification of no repeated values, and to the number of values that I decide,

so if I wanted to read 7 values, the output file would contain

21 22 23 24 17 18 19 - read in this order (reading in this order is important).

I am just setting out learning PERL, so please be gentle with me.

In reply to Reading the contents of a file from the bottom up by Scotmonk

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