What is linux error output redirection

In Linux, error output redirection refers to "writing error output information to a file"; output redirection is to re-specify the device to replace the monitor as the new output device, redirection In the computer, the execution result of a file or command is usually used instead of the keyboard as the new input device, and the new output device generally refers to the file.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What is Linux error output redirection

We know that the standard input device in Linux refers to the keyboard by default, and the standard output device refers to the monitor by default. The input and output redirection to be introduced in this section can be understood literally, that is:

• Input redirection: refers to reassigning the device to replace the keyboard as the new Input device;

• Output redirection: refers to reassigning the device to replace the monitor as the new output device.

Usually the execution result of a file or command is used to replace the keyboard as the new input device, and the new output device usually refers to the file.

What is input redirection?

In layman's terms, input redirection is to write the information to be input into the specified file.

What is output redirection?

In layman's terms, output redirection means writing the information to be output to a file, rather than outputting the file information to be output to the console (display)

What is error redirection?

In layman terms, error redirection is to write error information to a file

Linux output redirection

We use output redirection more often than input redirection. And, unlike input redirection, output redirection can also be subdivided into two technologies: standard output redirection and error output redirection.

For example, use the ls command to view the attribute information of two files respectively, but one of the files does not exist, as shown below:

[root@localhost ~]# touch demo1.txt
[root@localhost ~]# ls -l demo1.txt
-rw-rw-r--. 1 root root 0 Oct 12 15:02 demo1.txt
[root@localhost ~]# ls -l demo2.txt    <-- 不存在的文件
ls: cannot access demo2.txt: No such file or directory

In the above command, demo1.txt does exist , so some attribute information of the file is correctly output, which is also the standard output information of the command execution; demo2.txt does not exist, so the error message displayed after executing the ls command is the error output information of the command.

I emphasize again that if you want to write the data originally output to the screen to a file, these two types of output information must be treated differently.

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