Tests the value of an expression and, depending on the syntax
   specified, executes the following:

   o  One command following the THEN keyword if the expression is
      true

   o  Multiple commands following the $THEN command if the expression
      is true

   o  One or more commands following the $ELSE command if the
      expression is false

   Format

     $ IF  expression THEN [$] command


     or



     $ IF  expression


     $ THEN  [command]


     command

     .

     .

     .

     $ [ELSE]  [command]


     command

     .

     .

     .


     $ ENDIF

Additional information available:

PARAMETERS

examples

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 VMS DCL Concepts 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.

   1.  $ COUNT = 0
       $ LOOP:
       $ COUNT = COUNT + 1
          .
          .
          .
       $ IF COUNT .LE. 10 THEN GOTO LOOP
       $ EXIT

     This example shows how to establish a loop in a command
     procedure, using a symbol named COUNT and an IF statement.
     The IF statement checks the value of COUNT and performs an EXIT
     command when the value of COUNT is greater than 10.

   2.  $ IF P1 .EQS. "" THEN GOTO DEFAULT

       $ IF (P1 .EQS. "A") .OR. (P1 .EQS. "B") THEN GOTO 'P1'
       $  WRITE SYS$OUTPUT "Unrecognized parameter option ''P1' "
       $ EXIT
       $  A:       !  Process option a
        .
        .
        .
       $ EXIT
       $  B:       !  Process option b
        .
        .
        .
       $ EXIT
       $  DEFAULT: !  Default processing
        .
        .
        .
       $ EXIT

     This example shows a command procedure that tests whether a
     parameter was passed. The GOTO command passes control to the
     label specified as the parameter.

     If the procedure is executed with a parameter, the procedure
     uses that parameter to determine the label to branch to. For
     example:

         @TESTCOM A

     When the procedure executes, it determines that P1 is not null,
     and branches to the label A. Note that the EXIT command causes
     an exit from the procedure before the label B.

   3.  $  SET NOON

        .
        .
        .
       $  LINK CYGNUS,DRACO,SERVICE/LIBRARY
       $ IF $STATUS
       $ THEN
       $  RUN CYGNUS
       $ ELSE
       $   WRITE SYS$OUTPUT "LINK FAILED"
       $ ENDIF
       $ EXIT

     This command procedure uses the SET NOON command to disable
     error checking by the command procedure. After the LINK
     command, the IF command tests the value of the reserved global
     symbol $STATUS. If the value of $STATUS indicates that the LINK
     command succeeded, then the program CYGNUS is run. If the LINK
     command returns an error status value, the command procedure
     issues a message and exits.