An obscure shell command

1. REDIRECT Symbol

> Output redirected to a file or device overwriting the original file
>! Output redirected to a file or device forcing overwriting of the original file
>> output redirected to a file or device to append the original file
< redirect input to a program

2. Standard error redirection symbols

2> redirects a standard error output to a file or device overwriting the original file B-shell
2>> redirect a standard error output to a file or device appended to the original file
2>&1 redirect a standard error output to the standard output note: 1 could be the standard output.
>& redirect a standard error output to a file or device to overwrite the original file C-shell
|& to send a standard error pipe to another command as input

3.shell with (&&) and OR (| |)

If the first command executes successfully, the operator (&&) executes the second command
If the first command fails to execute, or the operator (| |) To execute a second command.

4. Find the file with the keyword "xxx" in the file name under the specified directory with the Find command
Find/Specify directory-name ' * keyword * '

5. Folder handling:
CP (copy) command: Cp-r/demo/em1/demo/em2/em2a
Note: Files under a folder are copied to other folders under the folder "CP File/This folder/Folder A", do not need-r, copy the folder to the other places in the computer before the folder to add/, the system can recognize the folder, otherwise it will prompt the error.
MV (move) command: mv/demo/em1/demo/em2
Note: To move a folder to a different folder, make sure that you cannot have a folder with the same folder name in the sibling directory

6.shell $1~ $n refers to the parameter values added to the shell, which is the 1th parameter, meaning to pass a parameter from the outside to $1,2 is the 2nd parameter

7.echo-e and Read-p

There is also the ability to output the specified content, but the output after read-p will all be displayed on the terminal display, and after echo-e can add other commands, such as line break and content display color, etc.

Input command: read-p "\nhello World" x

Output Result: \nhello World

Input command: ECHO-E "\nhello World"

Read X

Output command: ← This is the line break effect

Hello World

8.test! -D $dir

$dir is a path, and is a directory of false, can be combined with the summary of the 3rd use

9.ls-r/root

Recursively view all directories under Path root

Ten. 2>/dev/null

REDIRECT standard error output to an empty device

11.grep-v ' ^$ ' filter (delete) null character GREP-V reverse lookup

Grep-v-N ' ^$ ' filter (delete) blank line ^ represents line end

12.sed ' s/:.*$//g ' filter:. These content

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An obscure shell command