Use message replacement data along with the Command Analyzer Retrieve exit point.

In our last column, "Testing Your CL Program Error-Handling," we looked at a rather simplistic SNDESCAPE exit program and noted several assumptions in how the program is written:

• There is a separate exit program for each command that needs to be tested.
• There is no need to test error-handling in the MONESCAPE program that is based on replacement data within the CPF414E message.
• The program MONESCAPE is the only program in the current job that runs the DONOTHING command (otherwise, the SNDPGMMSG command will fail).

In this column, we will address the first two assumptions. In a subsequent column, we will look at how to avoid the third assumption.

Currently, the SNDESCAPE exit program does not check to see what command is running. It simply sends the escape message CPF414E (if the signed-on user is VININGTEST) whenever the program runs. Due to this implementation, a separate version of the exit program is needed for each command and escape message combination that you might want to test in terms of proper monitoring of various messages. The Command Analyzer Retrieve exit point does, however, provide information on what command is causing the exit program to run. This information is available in the parameter passed to the exit program, and we will look at this additional data now. Here is the source for an updated SNDESCAPE program:

Pgm        Parm(&Parm)                                          

Dcl        Var(&Parm)     Type(*Char) Len(38)                  

 Dcl        Var(&CmdName) Type(*Char) Stg(*Defined) +          

              Len(10) DefVar(&Parm 29)                         

Dcl        Var(&User)     Type(*Char) Len(10)                  

RtvJobA    User(&User)                                         

If         Cond(&User *Eq ViningTest) Then(Do)                 

           Select                                              

              When Cond(&CmdName = DONOTHING) Then(Do)         

                   SndPgmMsg MsgID(CPF414E) MsgF(QCPFMsg) +     

                     ToPgmQ(*Same (MonEscape)) MsgType(*Escape)          

                   EndDo                                        

              When Cond(&CmdName = XXX) Then(Do)                

                   SndPgmMsg MsgID(CPF415B) MsgF(QCPFMsg) +     

                     ToPgmQ(*Same (MonEscape)) MsgType(*Escape) 

                   EndDo                                        

              EndSelect                                         

           EndDo                                                

EndPgm                                                 

The single parameter passed by the Retrieve exit point is a structure providing quite a bit of information about the command running. The documentation for this structure can be found here. Of interest to us today is the name of the command being run. This can be found in positions 29 through 38 of the structure and is declared by this version of SNDESCAPE as variable &CmdName. Note that &CmdName is declared as *Defined over the structure &Parm. This use of Stg(*Defined) means that this version of the program requires that your system be at V5R4 or later. Earlier releases of the operating system can also check to see what command is being used but would require that you substring (%sst) the value of &CmdName out of the &Parm parameter. The %sst approach works but is less efficient in terms of program execution. Using *Defined storage is also much more self-documenting, to my mind anyway, in terms of understanding what the program is doing. To compile SNDESCAPE, you would still use CRTBNDCL VINING/SNDESCAPE.

As we are not interested in any of the information found beyond the command name, SNDESCAPE defines &Parm as being only 38 bytes in length, though a larger value (such as 76, which would match the exit point documentation) will do no harm. With the addition of &CmdName and the SELECT group, SNDESCAPE will now send CPF414E if the user VININGTEST is running the command DONOTHING and CPF415B if VININGTEST is running the command XXX. This is assuming that you also create the command XXX using the command CRTCMD CMD(VINING/XXX) PGM(VINING/DONOTHING) and register the SNDESCAPE program with the Command Analyzer exit point with this command:

ADDEXITPGM EXITPNT(QIBM_QCA_RTV_COMMAND) FORMAT(RTVC0100) PGMNBR(2)

   PGM(VINING/SNDESCAPE) PGMDTA(*JOB 20 'XXX       VINING')

(Note that there are seven blank spaces between the XXX and VINING. The command name must be blank padded to a full 10 characters when registering the exit program for a command.)

So we can now have one exit program sending various escape messages in support of testing different commands. We do, however, still have the limitation of no message replacement data. Furthermore, the commands must be running in a program named MONESCAPE (due to the TOPGMQ parameter of the SNDPGMMSG command used by SNDESCAPE).

Let's now take on the message replacement data aspect. Here is an updated SNDESCAPE that provides a device name of MYDEVICE when sending CPF414E:

Pgm        Parm(&Parm)                                          

Dcl        Var(&Parm)     Type(*Char) Len(38)                   

 Dcl        Var(&CmdName) Type(*Char) Stg(*Defined) +           

              Len(10) DefVar(&Parm 29)                          

Dcl        Var(&User)     Type(*Char) Len(10)                   

Dcl        Var(&Dta_414E) Type(*Char) Len(58)                   

 Dcl        Var(&Device)   Type(*Char) Stg(*Defined) +           

              Len(10) DefVar(&Dta_414E 41)                       

RtvJobA    User(&User)                                          

If         Cond(&User *Eq ViningTest) Then(Do)                  

           Select                                               

              When Cond(&CmdName = DONOTHING) Then(Do)          

                   ChgVar Var(&Device) Value(MyDevice)         

                   SndPgmMsg MsgID(CPF414E) MsgF(QCPFMsg) +    

                     MsgDta(&Dta_414E) ToPgmQ(*Same +          

                     (MonEscape)) MsgType(*Escape)             

                   EndDo                                        

              When Cond(&CmdName = XXX) Then(Do)               

                   SndPgmMsg MsgID(CPF415B) MsgF(QCPFMsg) +    

                     ToPgmQ(*Same (MonEscape)) MsgType(*Escape)

                   EndDo                                        

              EndSelect                                        

           EndDo                                               

EndPgm

The changes to SNDESCAPE are the following additions:

• The structure &Dta_414E is declared. This structure matches the replacement data defined for CPF414E with the length determined by using DSPMSGD RANGE(CPF414E), selecting option 2, and then adding up the storage for the various fields that are defined.
• The field &Device is declared. This field matches replacement variable &5 of CPF414E with the purpose and size determined by using options 1 and 2 of the previous DSPMSGD output. Notice that &Device is declared as being *Defined over the storage of &Dta_414E.
• Within the WHEN group, the variable &Device is set to a value of MyDevice. This variable, as a portion of the larger &Dta_414E structure, is then sent as replacement data with the CPF414E escape message.

To complement this change to program SNDESCAPE, we also make the following changes to MONESCAPE:

 Pgm                                                    

Dcl        Var(&X) Type(*Char) Len(50)                 

Dcl        Var(&Dta_414E) Type(*Char) Len(58)          

 Dcl        Var(&Device) Type(*Char) Stg(*Defined) +   

              Len(10) DefVar(&Dta_414E 41)             

Dcl        Var(&LenRplDta) Type(*Dec) Len(5 0) +       

              Value(58)                                

ChgVar     Var(&X) Value('A One')                      

XXX                                                    

MonMsg     MsgID(CPF415B) Exec( +                       

             Chgvar Var(&X) +                          

               Value(&X *TCat ', and a Two'))          

DoNothing                                             

MonMsg     MsgID(CPF414E) Exec(Do)                    

           RcvMsg MsgType(*Last) MsgDta(&Dta_414E) +  

             MsgDtaLen(&LenRplDta)

           If Cond(&Device = MyDevice) Then( +        

              Chgvar Var(&X) +                        

                Value(&X *TCat ', and a 414E'))       

           Else Cmd(ChgVar Var(&X) +                  

              Value(&X *TCat ',...'))                 

           EndDo                                      

ChgVar     Var(&X) +                                  

             Value(&X *TCat ', and a Three')          

SndPgmMsg  Msg(&X)                                    

Return                                                 

EndPgm         

These are the additions to MONESCAPE:

• We declare the structure &Dta_414E with the subfield &Device, as we did for SNDESCAPE.
• We declare the variable &LenRplDta to represent the length of the &Dta_414E structure.
• In the MONSMG MSGID(CPF414E) associated with the DONOTHING command, we use the Receive Message (RCVMSG) command to receive the last message sent to our program. When receiving the message, we ask for &LenRplDta bytes of replacement data to be returned to the &Dta_414E structure.
• Within the same MONMSG group, we test the value of variable &Device. If it's equal to the constant MyDevice, the program modifies variable &X with ',and a 414E'; otherwise, variable &X is modified with ',...'.

Both MONESCAPE and SNDESCAPE are now quite a bit more useful in terms of being able to test application changes in CL programs. SNDESCAPE can be used to test proper error-handling within MONESCAPE by selectively sending escape messages and, when appropriate, replacement data associated with the escape messages. We continue to have the limitation, though, that SNDESCAPE is hard-coded to only test a program named MONESCAPE. In the next column, we'll see how to eliminate this limitation.

More CL Questions?              

Wondering how to accomplish a function in CL? Send your CL-related questions to me at This email address is being protected from spambots. You need JavaScript enabled to view it.. I'll try to answer your burning questions in future columns.

Bruce Vining is president and co-founder of Bruce Vining Services, LLC, a firm providing contract programming and consulting services to the System i community. He began his career in 1979 as an IBM Systems Engineer in St. Louis, Missouri, and then transferred to Rochester, Minnesota, in 1985, where he continues to reside. From 1992 until leaving IBM in 2007, Bruce was a member of the System Design Control Group responsible for OS/400 and i5/OS areas such as System APIs, Globalization, and Software Serviceability. He is also the designer of Control Language for Files (CLF).A frequent speaker and writer, Bruce can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it.. 

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