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
NOTE
Digital advises against assigning a symbolic name that is
already a DCL command name. Digital especially discourages
the assignment of symbols such as IF, THEN, ELSE, and GOTO,
which can affect the interpretation of command procedures.
2 Parameters
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.
2 Examples
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.
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