How to use the ①$ notation: (Excerpt from-network)
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
②alias an alias to the command
Syntax: alias aliases = "Commands"
Example: Alias l= "Ls-lht test.sh"
Syntax knowledge for shell scripts 1