VMS Help IF, Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 expression

    Defines the test to be performed. The expression can consist of
    one or more numeric constants, string literals, symbolic names,
    or lexical functions separated by logical, arithmetic, or string
    operators.

    Expressions in IF commands are automatically evaluated during
    the execution of the command. Character strings beginning with
    alphabetic characters that are not enclosed in quotation marks
    (" ")  are assumed to be symbol names or lexical functions. The
    command language interpreter (CLI) replaces these strings with
    their current values.

    Symbol substitution in expressions in IF commands is not
    iterative; that is, each symbol is replaced only once. However,
    if you want iterative substitution, precede a symbol name with an
    apostrophe (')  or ampersand (&).

    The command interpreter does not execute an IF command when it
    contains an undefined symbol. Instead, the command interpreter
    issues a warning message and executes the next command in the
    procedure.

    For a summary of operators and details on how to specify
    expressions, see the OpenVMS User's Manual.

 command

    Specifies the DCL command or commands to be executed, depending
    on the syntax specified, when the result of the expression is
    true or false.