The meaning of special variables in the shell

Linux shell $$, $#, #!, $*, $, [email protected], $-, $0~$9 meaning
$$
Shell itself PID (process ID)
#*
All parameter lists. such as "$*" in the Case of "" ", in the form of" $ $ ... $n "output all parameters.
[Email protected]
All parameter lists. such as "[email protected]" with "" "in the case, with" $ "" $ "... All parameters are output in the form "$n".
$#
Number of parameters added to the shell
$?
End code of the last Run command (return value)
$0~$9
$ A is the name of the shell itself and can have up to 9 parameters behind $1~$9shell
$-
Flag at a glance using the SET command

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The meaning of special variables in the shell