eg:
cat test.sh 
#!/bin/bash
[ -e /etc/hosts ] && echo "ok" || echo "fail"
bash test.sh 
ok
eg:
cat test.sh 
#!/bin/bash
[ -e /etc/hostssssss ] && echo "ok" || echo "fail"
bash test.sh 
fail
注意這里 && 必須在 || 之前

[ -f /home/tecmint/Downloads/xyz1.txt ] || {touch /home/tecmint/Downloads/xyz.txt; echo "The file does not exist"}
“The file does not exist”