What $0,$1,$2 means in a Linux/unix script

There are three standard input and output in Linux, namely Stdin,stdout,stderr, the corresponding number is 0,1,2. STDIN is the standard input, read the information by default from the keyboard, stdout is the standard output, by default output output to the terminal, that is, the display and so on, stderr is a standard error message, the default will be displayed on the terminal. Since stdout and stderr are displayed by default on the terminal, in order to distinguish between the information, there is the definition of the number of 0,1,2, with 1 means that stdout,2 represents stderr.

$#: Number of command line arguments

$0: The name of the script

$?: Shell command execution result, if the previous instruction is executed correctly, the value is 0, error is not 0

What $0,$1,$2 means in a Linux/unix script