Use only one line eithor in bash script file or command line to display a digital clock. This line also shows some useful tricks in bash script

one_line_clock.sh

# Use only one line eithor in bash script file or command line to display a digital clock.
# This line also shows in bash script
# - A example of endless loop
# - Assigning output of command to a variable
# - "-n" "-e" of echo command
# - "\r" is used to reset the current line output

while sleep 1; do o=$(date); echo -n -e "\r$o"; done

monitor last file information

while sleep 1; do o=$(ll | tail -1); echo -n -e "\r$o"; done