BNF Notation

Command definitions are presented using the following rules (Backus Naur Form):


•      Terminal characters or words are Bold.  These are included in the command exactly as they appear, except that case is ignored.

•      Single terminal characters, or strings of symbols (for example, “<=”) are included with double-quotes.  Only the character(s) within the quotes would be included in the command.

•      Non-terminals (those things that have further definitions) are simply English descriptions where multiple words are connected with an underline character (e.g. file_specification).

•      Non-terminal definitions are specified following the symbol ::=.  This can be read “is defined as”.

•      Optional portions are presented within square brackets [ ].  The square brackets are NOT part of the command.  They would be omitted when entering the command.

•      Choices are separated by a vertical bar |, indicating that one of the choices must be made.

•      Choices within a command are grouped within parentheses ( ).  These are omitted if the entire definition would be enclosed.

•      Repetition within a command is indicated using braces { }.  Items within braces may be repeated zero or more times.

•      Comments are inserted following the ‘#’ symbol.  This is consistent with the script language.


Consider the following definitions.  A numeric value may be a number or a variable_value.  A number may start with a minus sign, then must consist of at least one digit, followed by optional digits:  Digits are the characters zero through ten.


             Digit ::= “0” | “1” | “2”  | “3” | “4” | “5” | “6” | “7” || “9”

             Number ::= [ “-“ ] digit { digit }

             Numeric_value ::= number | variable_value