linux-(16) Piping and redirection

The command behavior of Linux we provide a pipeline and redirection mechanism that enables multi-command collaboration through pipelines and redirects.

The data flow of the command-line shell is defined in the following three ways:

Name	Description	Number	Default
Stdin	Standard input	0	Keyboard
STDOUT	Standard output	1	Terminal
STDERR	Standard error	2	Terminal

command to receive parameters or data via stdin, through stdout output or through stderr output errors, through pipeline and redirection to control the data flow of the CLI

If the output is redirected to/dev/null there will be no output (this is usually used to filter the error message in the results)

Redirect:

> redirect stdout to file (overwrite), example: echo "xxx" > outfile

>> redirect stdout to file (append), example: echo "xxx" >> outfile

2> redirect stderr to file (overwrite), example: LS nothere 2> errout

2>&1 combining stderr with stdout, example: LS nothere 2>&1 alloutput

< redirect stdin, example: grep xxx </etc/passwd

Pipeline:

| (A vertical bar): The stdout of one command (the previous command) as the stdin of another command (the latter command), example: Ls-l | grep xxx

Pipelines are often used to combine different commands to implement a complex function that redirects an output or error message that is typically used to hold a command, which can be used to record execution results or to save an error message to a specified file.

linux-(16) Piping and redirection