Tuesday, August 9, 2016

Modernize your CL too

modernize your cl code using these techniques

I spent the end of last week assisting my colleagues with a project that involved creating CL programs, and over the weekend I was asked to check someone's CL code. In both cases I was disappointed to find that while these individuals have modernized their RPG skills, their CL skills are still date back to the 20th century.

In my opinion CL is a programming language which is undervalued in IBM i circles. I have met many developers who would rather use a complicated API in their RPG code, rather than use a simple CL command. It is time for everyone to look at all the tools that are available in IBM i, rather than limit themselves to just be a "RPG programmer".

Here are some of the things I think we should all do with our CL code.


CLLE, no more CLP

RPGLE was not the only ILE capable language that came out in V3R1, in 1994. ILE CL, CLLE, joined the party at the same time.

It is easy to convert a CLP source member to a CLLE some, just change the member type. The only command that I can think of that does not convert to CLLE is the Transfer Control command, TFRCTL, which can easily be replaced by a CALL command.

If you keep your source types in separate source files, you do not have to create another source file. CLLE member go in the QCLSRC source file.



One of the excuses I hear why people will not convert their source to CLLE is you cannot use the Retrieve CL Source command, RTVCLSRC. While that was valid for years, it is no longer so.

As part of IBM i 7.1 the RTVCLSRC command was enhanced to retrieve the source from CLLE programs and modules.


No more GOTO, use Do-loops

I am sure you use Do-loops in your RPG code, and shun Goto. It is time to do the same in your CL. DOWHILE, DOUNTIL, and DOFOR are all ready and waiting for you.



I cannot think of RPG without subroutines. You can do them in CL too, and the same principals apply. Rather than repeat code or call another CL program to do what you want use a subroutine.


No more nested Ifs, use Select

We have all seen blocks of code in CL of If statements where they are all executed despite only one being relevant. In 2004 V5R3 brought CL the SELECT command. It has the same functionality as the Select operation code in RPG. Use it as it will make your CL code less complicated and easier to follow.


Data structures

You can define and use the equivalent of data structures in CL. It it is easier, and faster, to use them rather than substring-ing the same string out of a larger variable every time you need it.


New BiFs

With IBM i 7.2 several new Built in Functions, BiFs, were introduced to make it easier to do some string handling in CL. I no longer have to call a RPG program or write many lines CL code to do the following:


You can write, update and delete records

Someone once said to me he could not take any programming language seriously if he could not write and update a file using it. By using the Run SQL Statement command, RUNSQL, I can do all of that.

Here are examples showing how it is possible, in CL, to delete a row/record from a table/file, add a row/record, and change it:

01  PGM


                 WHERE F1 = ''' || &VAR1 |<''' ') +

                VALUES (''' || &VAR1 |< ''',DEFAULT)') +
                   SET F2 = ''' || &VAR2 |< ''' +
                 WHERE F1 = ''' || &VAR1 |< ''' ') +



CL procedures

Most of the examples I have seen of procedures show RPG. It is possible to create CL procedures, and to use CL commands rather than complicated APIs to do the things CL does best.


Now you have seen that some of the biggest myths about CL have been busted. It is time to embrace modern CL and start using it in a 21st century manner.


This article was written for IBM i 7.2.


  1. I tackled this topic 14 years ago: I stood by my comments at the time. Today I am not too sure, but I would still say that it depends on the shop.

    1. Link to the article here (right click to open in new window)

  2. I couldn't agree with you more. Whether it's a project on its own or you simply convert each whenever you touch one, it's long over due.

  3. Ain't it amazing that any self-respecting i programmer would need to be reminded of these things!

    1. It still amazes me how many IBM i folks, especially the same ones who call themselves AS400 programmers, are out there doing things the same old way they did 20+ years ago.

      Come on guys! It is time to take the challenge to bring your skills up to the 21st century! Trust me it is fun learning and doing this stuff.

  4. Yes !! I have been doing this [modernize cl] after reading your earlier blogs on CL .. Thanks Simon !! ����

  5. Excellent note simon.Every legacy folks must go through it.

    1. Personally I dislike the "legacy" word when applied to the IBM i. It makes it sound staid and old fashioned, which it is not. Some of the programs that run on it... not so sure.

  6. Since CL is able to handle multiple files, structured programming, subroutines etc. and RPG got advanced to be free format like CL.

    It would be a good idea to unite both languages.

    Why do we need 2 syntaxes.

    If i need to add number of days to a CL variable tha contains a date, I need to have a separate RPG program just for this purpose.

    If I need to do a copy file, I need to have a separate CL program, or construct a string and use QCMDEXC, which is not so neat. and if i need to do RTVSYSVAL, it is imposible via QCMDEXC.

    Why not do it plain and simple, having just one language RPG. Issue a CL command from within RPG, similar to SQL statements in RPG.

    1. The concept sounds feasible, but even in your own words, you want to issue a CL command in RPG, or SQL statements from RPG.

      They are still separate languages. You couldn't execute a CL command in RPG if there wasn't Command Language. You couldn't execute an SQL statement in RPG if there wasn't a Structured Query Language.

      Each language has it's own purpose in life and can be intertwined as the programmer sees fit. IBM gave us interfaces to branch out from one language to another.

      Or maybe we want to do them one at a time. Imagine having to write and compile an RPG program just to execute a simple SQL statement.

      More importantly, we need all the commands so we can type them on the command line if we want to do them one at a time. We are lucky IBM decided to give us a bunch more commands to use in CL programs so we could do a bunch of commands all at once by just CALLing a CL program.

      After 35 years on the midrange platform going back to the S/38, I still feel spoiled having all the luxuries in CL. I also feel spoiled that IBM keeps adding more. Back on the S/38 there were a few hundred commands. Last time I checked we're now over 2000 commands. Pretty cool!

      PS. To get a system value from RPG, use the API QWCRSVAL. It's been there since at least V5R4.

  7. Simon, great read. CLLE vs CLP. I totally agree. If you update your RPGLE or COBOLLE , you will need to update the CLLE...


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