Linux Shell $ $n $* $# $$

Give you a full, you in the Linux environment to try to understand more:
The execution name of this program
$n the nth parameter value of this program, n=1..9
$* all parameters of this program, this option can have more than 9 parameters.
$# the number of parameters for this program
$$ the PID of this program (the current process ID number of the script run)
$! PID of the previous background instruction (process ID number of the last process running in the background)
$? Executes the return value of the previous instruction (displays the exit status of the last command. 0 means no error, any other value indicates an error)
$-shows the current options used by the shell, same as the SET command function
[email protected] is similar to $*, but can be used as an array

Md5sum: Generates and verifies the MD5 of the file.

In the network transmission, transfer between devices, copying large files, etc., may occur before and after the transmission of data inconsistencies. This is likely to occur in a relatively unstable environment such as the network. Then verifying the integrity of the file is also imperative.

Linux Shell $ $n $* $# $$