555*DBMS_PIPE.RECEIVE_MESSAGE(CHR(99)||CHR(99)||CHR(99),0)

What you posted isn’t valid PL/SQL as-is.

• CHR(99)||CHR(99)||CHR(99) evaluates to the string 'ccc', but you cannot pass a literal (or an expression) to an OUT parameter like RECEIVE_MESSAGE. The first parameter must be a variable that the procedure will fill.
• The 0 timeout means non-blocking: if a message is available in the pipe, it will be written to the buffer; if not, the buffer will typically be NULL after the call.

Correct usage (example):

• Declare a buffer, then receive into it:

DECLARE v_msg VARCHAR2(32767); BEGIN DBMS_PIPE.RECEIVE_MESSAGE(v_msg, 0); -- non-blocking IF v_msg IS NOT NULL THEN DBMS_OUTPUT.PUT_LINE('Received: ' || v_msg); ELSE DBMS_OUTPUT.PUT_LINE('No message available'); END IF; END; /

• If you want to wait for a message, specify a positive timeout (in seconds):

DECLARE v_msg VARCHAR2(32767); BEGIN DBMS_PIPE.RECEIVE_MESSAGE(v_msg, 5); -- wait up to 5 seconds IF v_msg IS NOT NULL THEN DBMS_OUTPUT.PUT_LINE('Received: ' || v_msg); ELSE DBMS_OUTPUT.PUT_LINE('No message after timeout'); END IF; END; /

Notes:

• Ensure the pipe is created and that another session has sent a message to it (using DBMS_PIPE.SEND_MESSAGE) before calling RECEIVE_MESSAGE.
• The maximum size of v_msg depends on your Oracle version; VARCHAR2(32767) is a safe upper bound in PL/SQL.