Informix Error -693: System command expects a non-null value.

Reasons / Common Causes

-693 fires when a SYSTEM statement's command argument evaluates to NULL — per the official guidance's example, a variable set to NULL passed to SYSTEM triggers this error.

1. A variable used as the SYSTEM command that was never assigned a value, per the official guidance's example — leaving it NULL by default.
2. A variable that legitimately became NULL (for example, from a failed lookup or an outer join) used as the SYSTEM command without a NULL check first.

Solutions / Resolution

1. Confirm the variable used as the SYSTEM command has actually been assigned a value before the SYSTEM statement runs.
2. Add a NULL check before the SYSTEM statement, if the command string is built from a value that could legitimately come back NULL:

   IF v_command IS NOT NULL THEN
     SYSTEM v_command;
   END IF;
   

Examples

The disallowed attempt

DEFINE v_command VARCHAR(200);
-- v_command was never assigned a value; it's NULL
SYSTEM v_command;
-- -693: v_command is NULL

Corrected

DEFINE v_command VARCHAR(200);
LET v_command = 'echo hello';
SYSTEM v_command;

Diagnostic Checks

1. Trace the value assigned to the SYSTEM statement's command argument back to its source, confirming it's guaranteed non-NULL by the time the SYSTEM statement executes.

Related Errors / Related Topics

• -668 — "The system command cannot be executed or it exited with a non-zero status." A related SYSTEM statement error, about the command's execution/exit status rather than a NULL argument.

Confirm the variable used as the SYSTEM command has actually been assigned a non-NULL value before the statement runs.