1: Standard input and output.
| device | Device file name | File descriptor | Types of |
| keyboard | /dev/stdin | 0 | Standard input |
| monitor | /dev/stdout | 1 | Standard output |
| monitor | /dev/stderr | 2 | Standard error output |
2: Output redirection (meaning that it should have been output to the monitor, now output to a file): the purpose is to facilitate management, but these commands must be output
| Types of | symbol | effect |
|---|---|---|
| Standard output redirection | Command> File | Overwritten method, output the correct command to the specified file or device |
| Command >> File | Append the correct output of the command to the specified file or device by appending | |
| Standard error output redirection | Error Command 2> File | Overwrite the way, output the error of the command to the specified file or device |
| Error command 2 >> file (no space between 2 and>) | In addition, output the error of the command to the specified file or device. |
Then use ls> abc
You will find that the new one will overwrite the old one. This is the difference between append and overwrite.
| Correct output and wrong output are saved at the same time | Command> File 2> & 1 | Overwritten method, save correct output and wrong output in the same file |
| Command >> File 2> & 1 | Added way to save correct output and wrong output in the same file | |
| Command &> File | Overwritten method, save correct output and wrong output in the same file | |
| Command & >> File | Added way to save correct output and wrong output in the same file | |
| Command >> File 1 2 >> File 2 | Append the correct output to file 1, and the wrong output to file 2. |
3: Input redirection
wc [options] [file name]
Options: -c count bytes
-w count words
-l count lines
After input, use ctrl + d to indicate that 4 lines of 4 words and 24 characters (including carriage return) are entered.
wc <filename
wc << character (end with the same character at the second occurrence)
