Dollars in Shell

As pointed out here (stackoverflow : link):

• Positional parameters ＄1 ,＄2,＄3… and their corresponding array representation, count and IFS expansion ＄@, ＄#, and ＄*.
• ＄- current options set for the shell.
• ＄＄ pid of the current shell (not subshell)
• ＄_ most recent parameter (or the abs path of the command to start the current shell immediately after startup)
• ＄IFS the (input) field separator
• ＄? most recent foreground pipeline exit status
• ＄! PID of the most recent background command
• ＄0 name of the shell or shell script