./bin/ls -a data
./bin/ls -s data
./bin/ls -sa data
./bin/chmod rw- rw- --- data/empty.txt
./bin/chmod r-- --- --x data/FIRST.txt
./bin/chmod rw- rw- rw- data/pwd.txt
./bin/chmod r-x r-x r-x data/yat.txt
./bin/chmod rwx --- --- data/.hidden.txt
./bin/chmod r-x --x r-- data/subdir
./bin/ls -ap data
./bin/head -n 1 Makefile
quit