$ ./bin/ls -a data
empty.txt
FIRST.txt
.hidden.txt
pwd.txt
subdir
yat.txt
$ ./bin/ls -s data
0 empty.txt
6 FIRST.txt
9 pwd.txt
22 yat.txt
$ ./bin/ls -sa data
0 empty.txt
6 FIRST.txt
5 .hidden.txt
9 pwd.txt
22 yat.txt
$ ./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
-rw-rw---- empty.txt
-r-------x FIRST.txt
-rwx------ .hidden.txt
-rw-rw-rw- pwd.txt
dr-x--xr-- subdir
-r-xr-xr-x yat.txt
$ ./bin/head -n 1 Makefile
#
$ quit