Shell $! The meaning of $#

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

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Shell $! The meaning of $#