[netrexx-pipelines] Ad writing filters/stages in oo/rexx (Re: Ad ooRexx scopes, ... (Re: Migrate OS/2 pipelines to NetRexx Pipes

[Rony G. F. <Ron...@wu...>]

Learned from René that it is possible to use external programs, also Rexx programs in NetRexx pipes 
like:

    pipe literal curl http://example.com | command | cons

So you can write oo/Rexx filter programs to be used as NetRexx pipe stages.

The oo/Rexx filter (reading from stdin, writing to stdout) would have to be written like:

    do until line=""
        parse pull line /* read from stdin */
        ... do something with line and if you want to pass on data do ...
        say editedData  /* writes to stdout */
    end

alternatively, one could write the Rexx filter also as (preferable):

    signal on notready /* raised if stdin gets closed */
    do forever
        parse linein line
        ... do something with line and if you want to pass on data do ...
        say editedData  /* writes to stdout */
    end
    notready:          /* label to jump to */

If you also want to write to stderr then you could either do that in classic Rexx style with "call 
lineout stderr,data" or in ooRexx ".error~say(data)".

You may want to look through these slides: 
<https://wi.wu.ac.at/rgf/wu/lehre/slides/BusinessProgramming/060_ooRexx_commands_V14.pdf>.

---rony



On 6/12/2022 12:47 PM, Rony G. Flatscher wrote:
>
> Hi Mike,
>
> sorry a glitch in the demo code that would not check for an asterisk in the first column, here the 
> corrected (hypothetical and untested code sample:
>
>     command='pipe console | sort | console' -- intensions: read from the console, sort, output to console
>     arrIn =.array~of("Max", "und", "Moritz", "diese", "beiden", "konnt", "...")
>     arrOut=.array~new
>     -- command gets input from ooRexx' arrIn, places stdout into arrOut
>     ADDRESS SYSTEM command WITH INPUT USING (arrIn) OUTPUT USING (arrOut)
>
>     -- now we need to postprocess the data received from the NetRexx pipe
>     -- assuming that each line is in the form of "varName=varValue",
>     -- lines that start with an asterisk (*) get ignored
>     -- create a directory of varName/varValue entries
>     dir=.directory~new
>     do line over arrOut -- process output of pipe line by line
>          *if left(line,1)="*" then iterate -- ignore lines starting with an asterisk*
>          parse var line varName '=' varValue
>          dir~setentry(varName,varValue)   -- setentry will uppercase the index varName automatically
>     end
>
>     -- now you decide what do to with the directory: use it to set Rexx variables in the current
>     -- context (in this very section of the code) or maybe return it to a caller who could use
>     -- the directory to set variables in its context
>
>     -- call BsfSetContextVariable("set",dir) -- will set the Rexx variable using dir
>     -- or:
>     --return dir -- will return the directory to the caller
>
> And an additional remark: if it is possible from NetRexx to call external programs in pipes, then 
> you could always inject ooRexx filters that read from stdin and write to stdout as demonstrated in 
> the above code.
>
> HTH,
>
> ---rony
>