The following bash script example we show some of the way how to check for an empty or null variable using bash:
#!/bin/bash if [ -z "$1" ]; then echo "Empty Variable 1" fi if [ -n "$1" ]; then echo "Not Empty Variable 2" fi if [ ! "$1" ]; then echo "Empty Variable 3" fi if [ "$1" ]; then echo "Not Empty Variable 4" fi [[ -z "$1" ]] && echo "Empty Variable 5" || echo "Not empty Variable 5"
Save the above script into eg. check_empty.sh
and execute with our without command line arguments:
$ bash check_empty.sh Empty Variable 1 Empty Variable 3 Empty Variable 5
Furthermore, the execution of the above script with a command line argument will trigger opposite results:
$ bash check_empty.sh hello Not Empty Variable 2 Not Empty Variable 4 Not empty Variable 5