shell note

while 循环

#!/bin/sh

while true; do
	echo "hello"
	sleep 1
done

for 循环

#!/bin/sh

for i in $(seq 1 10)  
do   
	echo $i
	sleep 1
done

如果变量未设置或设置为空字符串，则返回true

if [ -z "$var" ]
then
      echo "\$var is empty"
else
      echo "\$var is NOT empty"
fi

[ -z "$var" ] && echo "Empty"
[ -z "$var" ] && echo "Empty" || echo "Not empty"

[ ! -z "$var" ] || echo "Empty"
[ ! -z "$var" ] && echo "Not empty" || echo "Empty"