Exit a shell script with status n
can be 0 (success) or nonzero (failure). If n
is not given, exit status is that of the most recent command. exit
can be issued at the command line to close a window (log out). Exit statuses can range in value from 0 to 255.
if [ $# -eq 0 ]
echo "Usage: $0 [-c] [-d] file(s)" 1>&2
exit 1 # Error status