Redirection, pipe character, wildcard character, escape character under Linux

Output redirection

1, >Overwrite
2, >>Add
3, 2>Error message
4, 2>>Error message
5, &>Do not distinguish between correct and wrong
6, &>>Do not distinguish between correct and wrong

Pipe character

The standard output of the previous command is used as the standard input of the next command

Wildcard on the command line

1. *——Null value, unlimited
2 ,? Single character (not including empty characters)
3. [0-9] Numbers [a-z] [A-Z] Letters

Escape character

1. The backslash (\) turns a variable after the backslash into a simple string
2. The single quotation mark ('') transfers all variables in it to a simple string
3. The double quotation mark ("") keeps it The attribute of the variable is not transferred.
4. The backquote (``) returns the result after executing the command.
2 $ Process ID number of the current program