您可以将 -z 选项传递给 if 命令或条件表达式。如果STRING的长度为0,variable ($var)为空。test命令用于检查文件类型并比较值。这个页面显示了如何使用test命令确定bash shell变量是否为空。
判断 bash 变量是否为空：
要点：变量两端用双引号括起来
让我们看看语法和例子的细节。if命令的语法如下:
if [ -z "$var" ]
then
echo "\$var is empty"
else
echo "\$var is NOT empty"
fiOR
if test -z "$var"
then
echo "\$var is empty"
else
echo "\$var is NOT empty"
fi您还可以尝试控制操作符。语法如下:
[ -z "$var" ] && echo "Empty" [ -z "$var" ] && echo "Empty" || echo "Not empty"
OR
[[ -z "$var" ]] && echo "Empty" [[ -z "$var" ]] && echo "Empty" || echo "Not empty"
OR
## 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"
