判断字符串长度是否为零

#!/bin/bash
# testing string length

#-n 判断长度是否非零
#-z 判断长度是否为零

val1=testing
val2=''

if [ -n "$val1" ]
then 
    echo "The string $val1 is not empty"
else
    echo "The string $val1 is empty"
fi

if [ -z "$val2" ]
then 
    echo "The string $val2 is empty"
else
    echo "The string $val2 is not empty"
fi
if [ -z "$val3" ]
then 
    echo "The string $val3 is empty"
else
    echo "The string $val3 is not empty"
fi