1. Redirection command list
| command | Description |
|---|---|
| command > file | Redirect the output to file. |
| command < file | Redirect input to file. |
| command >> file | Redirect the output to file by appending. |
| n > file | Redirect the file with file descriptor n to file. |
| n >> file | Redirect the file with file descriptor n to file by appending. |
| n >& m | Combine the output files m and n. |
| n <& m | Combine the input files m and n. |
| << tag | Take the content between the opening tag tag and the closing tag tag as input. |
Note that file descriptor 0 is usually standard input (STDIN), 1 is standard output (STDOUT), and 2 is standard error output (STDERR).
2. Redirection in-depth explanation
Under normal circumstances, each Unix/Linux command will open three files when running:
- Standard input file (stdin): The file descriptor of stdin is 0, and Unix programs read data from stdin by default.
- Standard output file (stdout): The file descriptor of stdout is 1, and Unix programs output data to stdout by default.
- Standard error file (stderr): The file descriptor of stderr is 2, and Unix programs will write error information to the stderr stream.
(1) stderr redirects to file
$ command 2>file
stderr is appended to the end of the file
$ command 2>>file
(2) Redirect to file after stdout and stderr merge
$ command > file 2>&1 或 $ command >> file 2>&1
(3) Redirect stdin to file1 and stdout to file2
$ command < file1 >file2
Note: 0 is standard input (STDIN), 1 is standard output (STDOUT), and 2 is standard error output (STDERR).
There can be no space between 2 and> here. Only when 2> is one part, it means error output.
3./dev/null file
Do not display output results on the screen
$ command > /dev/null
Block stdout and stderr
$ command > /dev/null 2>&1