This challenge involves reversing the order of lines in a file.
This challenge applies to any input file containing a list of strings. However, we can re-use the 'generate-permutations.sh' script from the Generate Permutations challenge to produce a sufficiently large input file.
You can run the following from ../generate-permutations to generate an input file:
./generate-permutations.sh 0123456789 > permutations-10
The challenge is to reverse the order of lines in this file.
The output should be equivalent to running:
tac permutations-10 > permutations-10-reversed
On Mac OS X, you can also do this using tail:
tail -r permutations-10 > permutations-10-reversed
Note that this is very fast. This was the running time on an Intel Core i7-6850K, clocked at 3.60GHz:
$ time tac permutations-10 > permutations-10-reversed
real 0m0.119s
user 0m0.057s
sys 0m0.039s