Exit a shell script with status n (e.g., exit 1). n can be zero (success) or nonzero (failure). If n is not given, exit status will be that of the most recent command. exit can be issued at the command line to close a window (log out).
if [ $# -eq 0 ]; then
echo "Usage: $0 [-c] [-d] file(s)"
exit 1 # Error status