Explanation of the meaning of shell variables $#, $@, $0, $1, $2 in linux

Explanation of the meaning of shell variables $#, $@, $0, $1, $2 in linux:  Variable description:  $$  PID of Shell itself (ProcessID)  $!  The PID of the background Process that Shell runs  last $?  The end code of the last command to run (return value)  $  -List of Flags set by Set command  $*  List of all parameters. For example, when "$*" is enclosed in """, all parameters are output in the form of "$1 $2 ... $n".  $@  A list of all parameters. For example, when "$@" is enclosed in """, all parameters are output in the form of "$1" "$2" … "$n".  $#  The number of parameters added to the shell  $0  The file name of the shell itself  $1~$n  are added to each parameter value of the shell. $1 is the first parameter, $2 is the second parameter... .  #!/bin/bash printf "\$$ is $$ \n" printf "\$! is $! \n" printf "\$? is $? \n" printf "\$- is $- \n" printf "\$* is $* \n" printf "\$@ is $@ \n" printf "\$# is $# \n" printf "\$0 is $0 \n" printf "\$1 is $1 \n" printf "\$2 is $2 \n"