shell Variable

$1 - $9       these variables are the positional parameters.$0            the name of the command currently being executed.$#            the number of positional arguments given to this              invocation of the shell.$?            the exit status of the last command executed is              given as a decimal string.  When a command              completes successfully, it returns the exit status              of 0 (zero), otherwise it returns a non-zero exit              status.$$            the process number of this shell - useful for              including in filenames, to make them unique.$!            the process id of the last command run in              the background.$-            the current options supplied to this invocation              of the shell.$*            a string containing all the arguments to the              shell, starting at $1.$@            same as above, except when quoted.