shell特殊变量

变量 描述$0The filename of the current script.$nThese variables correspond to the arguments with which a script was invoked. Here n is a positive decimal number corresponding to the position of an argument (the first argument is $1, the second argument is $2, and so on).$#The number of arguments supplied to a script.$*All the arguments are double quoted. If a script receives two arguments, $* is equivalent to $1 $2.$@All the arguments are individually double quoted. If a script receives two arguments, $@ is equivalent to $1 $2.$?The exit status of the last command executed.$$The process number of the current shell. For shell scripts, this is the process ID under which they are executing.$!The process number of the last background command.