Author Archives: David

Regular Expressions in RPG

One of the things that RPG isn’t particularly good at is string scanning & manipulation.

Many other programming languages support using Regular Expressions (or regex, as they are often referred to). Java, PHP, Node.JS, Python, & Perl have support for regex’s built in.

Regular expressions are a very powerful tools for parsing, analyzing, and manipulating text. It should be noted, however, that with such power also comes the possibility for complexity. Some regular expressions can get VERY VERY complex. See the end of this post for a VERY complex expression.

A true regex master can create a functioning expression that is indistinguishable from modem line noise.

– Unknown (maybe me)
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Full Screen Windows 10 in MacOS Parallels

As a Mac user, I sometimes find my self needing to use Windows 10. To do this, I run it using the Parallels virtual machine manager.

One thing that bothered me, when was running Windows in full screen mode, was that the MacOS dock would pop up when I moved the mouse pointer to the Windows task bar.

I would have to move the mouse pointer away from the dock, let it drop back down, and then move the pointer back to the Windows task bar without going to the bottom of the screen.

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PCMLTOOLS

I’ve started a personal open source project. Something I’ve been meaning to do for quite a while.

The project is PCMLTOOLS — utilities designed to make working with the Java Toolkit for IBM i (JT400)’s Program Call Markup Language (PCML) easier to use.

The first tool is a Java class to allow a developer to retrieve a ProgramCallDocument object (which is normally generated from PCML) directly from a *PGM or *SRVPGM object who’s modules were compiled with the PGMINFO(*PCML:*MODULE) option.

The URL for the PCMLTOOLS project is https://github.com/fallingrock/pcmltools.

This is the first open source project that I’ve started … and I’m still getting the hang of github, so it may be rough around edges.

Don’t abandon unused domains

This is a general warning for anyone who owns or manages multiple internet domains.

If you have ever used a domain name, and switched to another one, you should never let the original domain expire.

The reason is, there are nefarious people out there who will buy that abandoned domain, put up content they scraped from an internet archive, and add links to malware or scam sites.

This happened to Ginny’s church’s web site (which I was hosting). They had a domain that had been used but was abandoned in favor of a new domain. Because the old domain wasn’t being used, and all the content had been migrated over, we decided to save some money and stop paying for it.

About a year after that, the domain popped up on the internet as a local church. I was confused by this and looked at the site. It was an almost exact copy of the last version that had been published … except it had links that tried to redirect people to scam sites.

The only thing we could do is file a complaint with the domain registrar. I’m not sure if they ever took it down.

Now, if I have a domain that I had used, I keep paying for it and just set it to do a permanent redirect to the new domain.

The only real exception to this is when I bought a domain with the intention of using it, but never got around to it. In those cases, I just let it lapse, because it’s not going to have content to mimic.

Back to Normal?

Illinois, and the majority of other states, are under mandatory “Stay at Home” or “Shelter in Place” orders. Here in Illinois the order is (currently) in place until the end of April. What happens then is anyones guess.

The big question is …

When will life return to normal?

– Everyone

I have a theory that’s not going to be very popular … and probably be viewed as cycnical.

In a nutshell: This IS the new “Normal”!

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Beware CHGCMDDFT

This is a general warning about using the CHGCMDDFT command to change the default value of command parameters for commands in QSYS.

Why Not?

There are a number of reasons not to change parameter defaults on commands in QSYS…

  1. Any time you upgrade your systems, those default parameter changes will be lost because the commands are completely replaced.
  2. Although you can identify what commands have had parameter defaults changed, there is no indication of WHAT parameter defaults were changed on a command. To identify what commands have had defaults changed display the command objects description (DSPOBJD) with DETAIL(*SERVICE). If an object has had the parameter defaults changed, the APAR ID will show ‘CHGDFT’.
  3. Third party products may be expecting commands to have the IBM provided default values. Because 3rd party products usually have to work on a number of IBM i versions, it’s impossible for vendors to specify a specific value for every parameter. New parameters are added with almost every release.

A Better Approach

A better approach would be to create a library to hold copies of the commands you want to modify …

  1. Create a specific library to hold customized commands
  2. Add that library to the QSYSLIBL system value above QSYS
  3. Duplicate the *CMD objects into that library
  4. Change the default parameter values on the commands in that library.

This way the commands in QSYS are left with the IBM provided default parameter values. Since the custom command library is above QSYS in the system library list, applications that reference those command (that don’t qualify the command to QSYS), will use the modified command.

I like to create a simple CL program that does the work of deleting existing commands from the custom command library, duplicate the command from QSYS, and modifies the command parameter defaults. Not only does this make it easy to recreate the custom command parameter defaults when you do an OS upgrade, it documents what parameter defaults have been made.

CRTPRXCMD

You may be tempted to use the CRTPRXCMD to create a ‘proxy command’, that points to the original command, and change the defaults on the proxy command.

DO NOT DO THAT!

A proxy command isn’t a stand alone object that is independent of the actual command. It’s just a pointer to the real command.

Any real changes you make to a proxy command will actually be made on the real command.

Example

Here’s a very simple example of a CL that will repopulate a custom command library with modified default parameter values.

PGM

DCL        VAR(&LIB) TYPE(*CHAR) LEN(10) VALUE('CUSTCMD')
DCL        VAR(&CMD) TYPE(*CHAR) LEN(10)

/* SAVLIB must default to *PRV target release for compatiblity */
CHGVAR     VAR(&CMD) VALUE('SAVLIB')
CALLSUBR   SUBR(DUPCMD)
CHGCMDDFT  CMD(&LIB/&CMD) NEWDFT('TGTRLS(*PRV)')

RETURN

SUBR       SUBR(DUPCMD)
   DLTCMD     CMD(&LIB/&CMD)
   MONMSG     MSGID(CPF2105)

   CRTDUPOBJ  OBJ(&CMD) FROMLIB(QSYS) OBJTYPE(*CMD) TOLIB(&LIB)

ENDSUBR


ENDPGM  

Java and External Data Structures on IBM i

One of my favorite techniques for passing structured bulk data around is using datas queue’s with the format of the data defined in an external data structure.

In RPG this is very easy … you defined a data structure using the EXTNAME keyword.

dcl-ds stuct1 extname('EXTDS1') end-ds;  

Then you just use the data structure name when calling the QRCVDTAQ or QSNDDTAQ api’s and the data will be nicely mapped into the appropriate structure field.

But what if you wanted to allow a Java application to consume or populate the data queue?

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Automatic Snapshots on Lightsail

The folks at Amazon Lightsail have added a new, much needed, feature: Automatic snapshots.

Shapshots are a way of creating an exact backup of your Lightsail instance. You can use this snapshot to move the instance to another region, move it to the more flexible EC2 platform, or just create a new instance based on an existing one.

Previously, the only way to automate snapshots was to create AWS Lambda functions with Cloudwatch triggers. I was able to get that setup, but it took quite a while.

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