Bash

Check for a particular file size.

du -sh <filename>

Find listening port on Mac

netstat -an | grep -i listen | grep 80
netstat -an | grep LISTEN | grep 80

Set

set -x  # debug
set -e  # exit the script when there is an error
set -o pipeline  # exit when there is an error in pipe command

AWK

# Grep column 1 and 4
echo employee.txt | awk '{print $1 $4}'