Logical test of Linux basic commands one

1. Determine the result of a command using test, which returns 0, or an integer. Returns 0 for true, returns an integer indicating the error code

2. Get the return result of the previous command using $?

3. For example

My server has/home/www such a folder, so ls/home/www The return result of this command is 0;

That is, echo $? Returns a value of 0

My server does not exist/home/kkk such a folder, so ls/home/kkk the return of this command is the command after the execution of the error code;

That is, echo $? Returns a result of 2. This 2 indicates that the file or folder does not exist.

4. Commonly used file test characters

-E Indicates whether this file name exists

-F Indicates whether this filename is a file

-D Indicates whether this file name is a folder

-R Indicates whether this file name is readable

-W Indicates whether this file is writable

-X Indicates whether this file is executable

-S Indicates whether this file asks the socket

4.1/home/www to a folder on my server

So the result of Test-e/home/www is 0, which is true, this file name exists

So the result of Test-f/home/www is not 0, which is false, this filename is not a file

So the result of Test-d/home/www is 0, which is true, this file is named folder

4.2/HOME/KKK This file name does not exist on my server

So the result of Test-e/home/kkk is not 0, which is false, this file name does not exist

So the result of test-d/home/kkk is not 0, which is false, this file name does not ask the folder.

Logical test of Linux basic commands one