IF

##
IF

            [SIC\]IF Logical_Expression [THEN]
            [SIC\]IF Logical_Expression Command [Arguments]

        The first form starts a conditional IF block. The behaviour of IF blocks
        is similar to structured Fortran. The THEN keyword is optional.
        The  second  form  defines a logical IF statement, i.e. it uses a single
        line with no possibility of alternate execution (no ELSE  choice).  When
        the argument following the logical expression is not THEN, it is assumed
        to be a command which will be interpreted, together with the next  argu-
        ments, if the logical expression evaluates as true.

        This  command can only be used within a procedure: interactive users are
        expected to be able to make their decisions themselves.

        The logical expression must be a single argument (no blanks);  composite
        expressions  using  .AND. or .OR. operators are supported. Logical func-
        tions like EXIST, FILE, or FUNCTION can also be used (see HELP  FUNCTION
        for details).