1.$ IF P1 .EQS. "HELP" THEN GOTO TELL
      $ IF P1 .EQS. "" THEN GOTO TELL
         .
         .
         .
      $ EXIT
      $ TELL:
      $ TYPE SYS$INPUT
      To use this procedure, you must enter a value for P1.
         .
         .
         .
      $ EXIT

      In this example, the IF command checks the first parameter
      passed to the command procedure; if this parameter is the
      string HELP or if the parameter is not specified, the GOTO
      command is executed and control is passed to the line labeled
      TELL; otherwise, the procedure continues executing until the
      EXIT command is encountered. At the label TELL, a TYPE command
      displays data in the input stream that documents how to use the
      procedure.

    2.$ ON ERROR THEN GOTO CHECK
         .
         .
         .
      $ EXIT
      $ CHECK:  ! Error handling routine
         .
         .
         .
      $ END:
      $ EXIT

      The ON command establishes an error-handling routine. If any
      command or procedure subsequently executed in the command
      procedure returns an error or severe error, the GOTO command
      transfers control to the label CHECK.