Shell判断字符串变量是否为空的方法实现_linux shell

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

if test -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 "Empty" || echo "Not empty"

## 检查 $var 是否设置使用! 即检查 expr 是否为假 ##
[ ! -z "$var" ] || echo "Empty"
[ ! -z "$var" ] && echo "Not empty" || echo "Empty"
 
[[ ! -z "$var" ]] || echo "Empty"
[[ ! -z "$var" ]] && echo "Not empty" || echo "Empty"