getjobid, cl, and liblist — Oh, My!

6 minute read

With the latest update to BASH, there are 3 new IBM i-specific BASH builtin functions: liblist, cl, and getjobid. These builtins function nearly identically to the liblist, system, and getjobid commands that exist in PASE and/or QSH.

If these commands already exist, why add them to BASH? Let’s explore:

$ /QOpenSys/usr/bin/getjobid
Process identifier 1575015 is 073984/QSECOFR/QP0ZSPWT
$ /QOpenSys/usr/bin/getjobid
Process identifier 1575016 is 073985/QSECOFR/QP0ZSPWT
$ /QOpenSys/usr/bin/getjobid
Process identifier 1575017 is 073986/QSECOFR/QP0ZSPWT

Every time I run getjobid, I’m getting the job id of the getjobid process, not my shell’s jobid. If I want to get my shell’s job id, I have to remember to pass the shell’s pid (which is helpfully in the $$ special variable)

/QOpenSys/usr/bin/getjobid $$

Kind of a pain, but once you figure it out it’s not sooooo bad.

CL to the Rescue?

Ok, so now let’s say I am trying to run a PASE program which is running in to problems while calling some ILE code. The ILE code is writing messages to the job log, but the job log isn’t being saved due to the log level of the job! Let’s use the system command to change the log level:

/QOpenSys/usr/bin/system "CHGJOB LOG(4 00 *SECLVL)"

If I run this, I will get no difference in behavior.

$ /QOpenSys/usr/bin/system 'dspjob' | grep -E -A3 'LOG$'
   Message logging:                                 LOG
     Level  . . . . . . . . . . . . . . . . . . :                4
     Severity . . . . . . . . . . . . . . . . . :                0
     Text . . . . . . . . . . . . . . . . . . . :                *NOLIST

What gives? Oh, duh! I forgot to add the -i flag to run in the current process. Silly me. Wait, even after adding -i, it’s still not working. womp, womp

What is going on? Well, if you understand the Unix process model, this does starts to makes sense: we executed the system command, causing BASH to start a new process in which the system command starts up (and if the -i flag is not passed, system spawns an additional job), calls CHGJOB, and immediately exits. It sort of looks like this:

bash
└── system -i ... -> CHGJOB

bash
└── system ...
    └── <spawned job> -> CHGJOB

In either case, this is quite pointless (even more so without -i), as it still hasn’t affected our job. Luckily, the CHGJOB command supports passing in a job name, so we can use getjobid to retrieve it:

/QOpenSys/usr/bin/system "CHGJOB JOB($(/QOpenSys/usr/bin/getjobid -s $$)) LOG(4 00 *SECLVL)"

What a pain in the butt! Of course this only works because CHGJOB allows you to specify a job name to affect. Other CL commands are not so lucky, like ADDLIBLE or CHGCURLIB :disappointed:

Bash to the Rescue

Ok, so back to BASH. Because these new functions are builtins and not commands, they execute in BASH itself, ie. the current job. This means when we run getjobid it gives you what you probably expected:

$ getjobid
Process identifier 1574877 is 073846/QSECOFR/QP0ZSPWT
$ getjobid
Process identifier 1574877 is 073846/QSECOFR/QP0ZSPWT
$ getjobid $$
Process identifier 1574877 is 073846/QSECOFR/QP0ZSPWT

In addition, we also have a cl function, which behaves almost the same as system, except it defaults to running in the current job, so no -i is needed. With that, we don’t even need getjobid for the above example:

cl "CHGJOB LOG(4 00 *SECLVL)"

And of course with builtins, it’s finally possible to implement a liblist utility to change the library list of PASE jobs:

$ liblist -a kadler
CPC2196: Library KADLER added to library list. 
$ liblist -d kadler
CPC2197: Library KADLER removed from library list.
$ liblist -c kadler
CPC2198: Current library changed to KADLER.
$ liblist
QSYS        SYS  
QSYS2       SYS  
QHLPSYS     SYS  
QUSRSYS     SYS  
QSHELL      PRD  
KADLER      CUR  
QGPL        USR  
QTEMP       USR  
QDEVELOP    USR  
QBLDSYS     USR  

And because we’re using the the LIBRARY_LIST_INFO SQL service, we get the schema name for free so I figured why not add a -s option?

$ liblist -a LONGSCHEM
CPC2196: Library LONGSCHEM added to library list.

$ liblist -s
QSYS        SYS  QSYS
QSYS2       SYS  QSYS2
QHLPSYS     SYS  QHLPSYS
QUSRSYS     SYS  QUSRSYS
QSHELL      PRD  QSHELL
KADLER      CUR  KADLER
LONGSCHEM   USR  longschemaname
QGPL        USR  QGPL
QTEMP       USR  QTEMP
QDEVELOP    USR  QDEVELOP
QBLDSYS     USR  QBLDSYS

Note that for compatibility with QSH liblist, the default output is kept the same.

Finally, ff that wasn’t enough, if you ever forget what the command line arguments do, we have much better help text than the PASE or QSH equivalents :grin:

$ cl --help
cl: cl [-beEhiIkKnOpqsSv] COMMAND [ARG ...]
    Executes a CL command.
    
    Options:
      -i        Run COMMAND in the current job (default)
      -S        Run COMMAND in a spawned job
      -K        Keep all spool files generated by COMMAND and the job log
      -k        Keep all spool files generated by COMMAND
      -n        Do not include the message identifier when writing the messages to standard error
      -p        Only write the messages sent to the program's message queue by COMMAND to standard error
      -q        Do not write messages generated by COMMAND to standard error
      -s        Do not write spool files generated by COMMAND to standard output
      -v        Write the complete command string to standard output before executing it
    
      -b        Force binary mode for standard streams used by the CL command
      -e        Copy PASE for i environment variables to ILE before running COMMAND
      -I        Force CCSID conversion for standard input used by COMMAND
      -O        Force CCSID conversion for standard output used by COMMAND
      -E        Force CCSID conversion for standard error used by COMMAND
    
    Arguments:
      COMMAND   The CL command to run.
      ARG       One or more arguments to pass to the CL command

Questions, Caveats, and More

Checking for support

These builtins are available once you install bash 4.4-3. You can check if you have the support and ensure you’re using the builtin by using the type builtin:

$ type liblist
liblist is a shell builtin
$ type cl
cl is a shell builtin
$ type getjobid
getjobid is a shell builtin

Note, the which command will give you different results, since which is an external command and not a BASH builtin:

$ which getjobid
/QOpenSys/usr/bin/getjobid

How do I use them?

Just call them like you would any other command. It’s likely you’re already using BASH builtins and didn’t even know it! (Things like echo, cd, and even more used in scripting are also BASH builtins.)

When BASH has a builtin, it takes precedence over any external command found on the $PATH:

$ which getjobid
/QOpenSys/usr/bin/getjobid
$ type getjobid
getjobid is a shell builtin

Why ‘cl’ and not ‘system’?

While both getjobid and liblist match the names their PASE/QSH counterparts, we decided not to do the same with cl — even though it has all the same options. We did initially have it as system, but there was concern that too many existing PASE scripts relied on system and depending on whether you ran a script in bash vs bsh, ksh, etc you could get unexpected behavior.

You can always create a BASH alias for system if you like. Run the following or add it to one of BASH’s startup files (eg. ~/.bashrc):

alias system=cl

In addition, because we didn’t have to worry about full compatibility with system, we could change the default behavior to running in the current job, which is probably what you want most of the time anyway. :tada: This means no -i is not needed (but supported for compatibility) and also a new builtin-specific option -S has been added to force cl to spawn a new job. This spawned job will run in a non-multithreaded job and without PASE loaded, which can be useful for some commands.

How do I run the non-builtin version?

Since builtins have higher precedence over external commands, changing your $PATH will have no effect. You need to either fully qualify the command or disable the shell builtin.

# Fully qualify getjobid
/QOpenSys/usr/bin/getjobid

# Disable getjobid builtin for the current session
enable -n getjobid