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In linux, redirection is to redirect the data information that is supposed to be output to a specific file, that is, to change the default execution of the original system command; redirection is generally achieved by inserting specific symbols between commands. The syntax example is "command1 > file1".

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

What is redirection in linux

Linux redirection refers to modifying some of the original default things, changing the default execution mode of the original system commands, for example, simply I do not want to see the output in the monitor but want to output to a file, I can do this work through Linux redirection.

1What exactly is redirection in Personalized Linux?

Redirection in Linux is to redirect the data information that is supposed to be output to the screen to a specific file or to a black hole (/ dev/null).

1.2 what is the use of redirecting?

1, when the program executes a lot of output information, it needs to be saved for paging view.

2, the program executed in the background will generally have output, do not want its output to interfere with the terminal.

3. Perform scheduled backup tasks and want the backup results to be retained.

4. When the user is created repeatedly, some error messages will be prompted, and the information can be discarded directly.

5, when you want to save the error log and the correct log to different files.

1.3 Standard input and output

When a process manipulates a file:

1. First of all, the process cannot access the hardware directly, so you need to use the kernel to access the file.

2, and the kernel kernel needs to use the file descriptor (file descriptor) to access the file.

Summary: process-through-> file descriptor (non-negative integer)-access-"file name; the process uses file descriptors to manage open file correspondence.

Step 1: run tail-f / etc/passwd

Part II: through the file descriptor 3murmury-> / etc/passwd-- > inode-- > block

Step 3: output correctly-> by default, through the file descriptor 1: talk-> current terminal 1 > (change the location of the output, file, black hole)

Step 4: error output-- > by default, through the file descriptor 2murmuri-"current terminal 2 > (error output)"

Usually, a program accesses a file and opens at least three standard files, namely, standard input, standard output, and error output.

The process will get the data from the standard input, print the normal output to the screen terminal, and print the wrong output information to the screen terminal.

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