$TEST

Contains the truth value resulting from the last command using the timeout option.

Synopsis

$TEST
$T

Description

$TEST contains the truth value (1 or 0) resulting from the last command with a timeout. $TEST is set by the following commands, regardless of whether they are entered from the Terminal prompt or encountered in routine code:

A timed JOB sets $TEST to 1 if the attempt to start the new job succeeds before the timeout expires. If the timeout expires, $TEST is set to 0.
A timed LOCK sets $TEST to 1 if the lock attempt succeeds before the timeout expires. If the timeout expires, $TEST is set to 0.
A timed OPEN sets $TEST to 1 if the open attempt succeeds before the timeout expires. If the timeout expires, $TEST is set to 0.
A timed READ sets $TEST to 1 if the read completes before the timeout expires. If the timeout expires, $TEST is set to 0.

Issuing these commands without a timeout does not set $TEST.

Note:

$TEST is also set by the legacy version of the IF command. It is neither set nor checked by the current block-structured IF command. When the test expression of a legacy IF command is evaluated, $TEST is set equal to the resulting truth value. In other words, if the IF expression tests true, $TEST is set to 1. If it tests false, $TEST is set to 0 (zero).

Setting $TEST

You can use the SET command to set $TEST to a boolean value. A value of 1, or any non-zero numeric value, sets $TEST=1. A value of 0, or a non-numeric string value, sets $TEST=0.

$TEST can be set by any command or function that can return a logical condition.

Maintaining $TEST

A successful JOB, LOCK, OPEN, or READ command that did not specify a timeout does not change the existing value of $TEST.

The DO command maintains the value of $TEST when calling a procedure, but not when calling a subroutine. For details, refer to the DO command.

The ZBREAK command maintains the value of $TEST when calling execute_code. For details, refer to the ZBREAK command.

Example

The following code performs a timed read and uses $TEST to test for completion of the read.

   READ !,"Type a letter: ",a#1:10
   IF $TEST { DO Success(a) }
   ELSE { DO TimedOut }
Success(val)
   WRITE !,"Received data: ",val
TimedOut()
   WRITE !,"Timed out"

Notes

Operations That Do Not Set $TEST

JOB, LOCK, OPEN, and READ commands without a timeout have no effect on $TEST. Postconditional expressions also have no effect on $TEST.

The block-oriented IF command (which defines a block of code by enclosing it in curly braces) does not use $TEST in any way. The following invocations of the legacy IF command also do not use $TEST: legacy IF without an argument and the ELSE command have no effect on $TEST.

Unsuccessful Timed Operations

Caché does not produce an error message after an unsuccessful timed operation. Your application must check $TEST and then produce an appropriate message.