Follow the rules for REXX execs: A well behaved REXX check will adhere to all the rules for writing a REXX exec. See:

• z/OS MVS Programming: Authorized Assembler Services Guide
• z/OS TSO/E REXX User's Guide
• z/OS TSO/E REXX Reference. See the topic on conditions and condition traps for recovery information.

Release any system resources obtained: A REXX check should release any resources it obtains, such as a data set, for example, before the REXX check stops running. The REXX check must also include logic that releases resources when an unexpected non-exception condition, such as a time-out or CANCEL, occurs. For information about how System REXX manages unexpected conditions, see:

• System REXX in z/OS MVS Programming: Authorized Assembler Services Guide
• The section on conditions and condition traps in z/OS TSO/E REXX Reference.

The following example shows how our SYS1.SAMPLIB check, HZSSXCHK, frees resources for an unexpected condition:

/*********************************************************************/
/*                                                                   */
/* HZS_SAMPLE_REXXTSO_CHECK unexpected conditions:                   */
/* SYNTAX, ERROR, FAILURE, NOVALUE and HALT are specified by the     */
/* SIGNAL function and receive control when an unexpected event      */
/* occurs.                                                           */
/*                                                                   */
/*  - Report the line in error                                       */
/*  - Free the input data set if it is allocated                     */
/*  - DISABLE the check and exit                                     */
/*                                                                   */
/*********************************************************************/
 SYNTAX:
 ERROR:
 FAILURE:
 NOVALUE:
 HALT:
ERR1 = "An Error has occurred on line: "Sigl
ERR2 =  sourceline(sigl)
Say Err1
Say "Line "Sigl" text: "Err2
ADDRESS TSO "FREE DSN("DataSetName")"
HZSLFMSG_REQUEST = "STOP"         /* Disable the check               */
HZSLFMSG_REASON = "ERROR"
HZSLFMSG_DIAG   =  Right(RC,16,0) /* report the decimal rc in the
                                     HZS1002E message and the check
                                     display detail                  */
HZSLFMSG_RC = HZSLFMSG()
IF HZS_PQE_DEBUG = 1 THEN
 DO                               /* Report debug detail in REXXOUT  */
   SAY "PARMS: "HZS_PQE_PARMAREA
   SAY "HZSLFMSG RC"  HZSLFMSG_RC
   SAY "HZSLFMSG RSN" HZSLFMSG_RSN
   SAY "SYSTEMDIAG"   HZSLFMSG_SYSTEMDIAG
 END
 EXIT               /* The check is not performed          */

Have your REXX check stop itself when the environment is inappropriate: If your check encounters an environmental condition that will prevent the check from returning useful results, your check should stop itself and not run again until environmental conditions change and your code requests it to run. Your check should do the following to respond to an inappropriate environment:

1. Issue the HZSLFMSG function to stop itself:

   HZSLFMSG_REQUEST = "STOP"
   HZSLFMSG_REASON = "ENVNA"
   HZSLFMSG_RC = HZSLFMSG()

2. Issue an information message to describe why the check is not running. For example, you might issue the following message to let check users know that the environment is not appropriate for the check, and when the check will run again:

   The server is down. 
   When the server is available, the check will run again.

3. Make sure that your product or check includes code that can detect a change in the environment and start running the check again when appropriate. To start running the check, issue the following HZSCHECK service:

   HZSCHECK REQUEST=RUN,CHECKOWNER=checkowner,CHECKNAME=checkname

   If the environment is still not appropriate when your code runs the check, it can always stop itself again.

Save time, save trouble - test your check with these commands: When you have written your check, test it with the following commands to find some of the most common problems people make in writing checks:

F hzsproc,UPDATE,CHECK(check_owner,check_name),DEBUG=ON
F hzsproc,UPDATE,CHECK(check_owner,check_name),PARM=parameter,REASON=reason,DATE=date
F hzsproc,DELETE,CHECK(check_owner,check_name),FORCE=YES
F hzsproc,DISPLAY,CHECK(check_owner,check_name),DETAIL