shell scipt logic方括号旁边的空格不可省略

Here are some examples using the conditional expressions just listed.

Note that the spaces on either side of the square brackets are not optional!

if [ $carprice -gt 20000 ]

数字和字符串比较的指令也不同

So what kind of conditions can we test for? If you're dealing with numbers, here are the conditional expressions you can use. In other words, any of these expressions can go inside the brackets on the if or elif statement:

num1 -eq num2 True if num1 equals num2.

num1 -ne num2 True if num1 is not equal to num2.

num1 -lt num2 True if num1 is less than num2.

num1 -gt num2 True if num1 is greater than num2.

num1 -le num2 True if num1 is less than or equal to num2.

num1 -ge num2 True if num1 is greater than or equal to num2.

If you're comparing character strings, these are the valid conditional expressions:

str1 = str2 True if str1 and str2 are identical.

str1 != str2 True if str1 and str2 are not identical.

-n str1 True if str1 is not null (length is greater than zero).

-z str1 True if str1 is null (length is zero).