shell 字符串关系运算

运算符  说明 

=          检测两个字符串是否相等，相等返回 true。 

!=         检测两个字符串是否不相等，不相等返回 true。

-z         检测字符串长度是否为0，为0返回 true。

-n         检测字符串长度是否不为0，不为0返回 true。 

             检测字符串是否不为空，不为空返回 true。 

示例：

#!/bin/sh

a="abc"
b="def"
c=""

if [ $a = $b ]
then
   echo "a is equal to b"
else
   echo "a is not equal to b"
fi

if [ $a != $b ]
then
   echo "a is not equal to b"
else
   echo "a is equal to b"
fi

if [ -z $a ]
then
   echo "string a length is zero"
else
   echo "string a length is not zero"
fi

if [ -z $c ]
then
   echo "string  c length is zero"
else
   echo "string  c length is not zero"
fi

if [ -n $a ]
then
   echo "string a length is not zero"
else
   echo "string a length is zero"
fi

if [ $a ]
then
   echo "string a is not empty"
else
   echo "string a is empty"
fi

if [ $c ]
then
   echo "string c is not empty"
else
   echo "string  c is empty"
fi

if [ $d ]
then
   echo "string d is not empty"
else
   echo "string  d is empty"
fi

if [ -z $d ]
then
   echo "string d length is zero"
else
   echo "string d length is not zero"
fi

结果：

a is not equal to b
a is not equal to b
string a length is not zero
string  c length is zero
string a length is not zero
string a is not empty
string  c is empty
string  d is empty
string d length is zero