shell 字符串比较是否相等 报错[: =: unary operator expected

shell 字符串比较是否相等  报错[: =: unary operator expected

egg:

a = '123'

b='1234'

if [  $a  ==  $b ]；then

echo "相等"

fi

此时报错[: =: unary operator expected

正确写法  多加个[ ]：

if [[  $a  ==  $b ]]；then

echo "相等"

fi