Hi,
Got curious:
A) Your sendkeys manipulate Qcad by sending shortcut commands to the command line ?
Q: does that work out? What numbers are you parsing and how are they treated (rounded/truncated)?
B) You didn’t retrieve data from Qcad in any form yet ?
Scripting in Qcad is in ECMAscript or JavaScript.
The length of a drawing entity in scripts is simply REntity.getLength()
That is when you have the entity at hand otherwise one has to query that from the drawing by id.
Querying a selection works.
Q: How does sendkeys make the selection among others ?
Maybe that is why you noticed:
Then Select All (TA) would work out.
Maybe you can sendkeys to start the ScriptShell and trow in a simple script.
In the Shell javascript returns every line with a result.
Can one read , copy / cut that return?
qDebug() sends it messages to stdout except on win:
But a script can easily write to a CSV, a log, … too:
One doesn’t need a full blown GUI script but those can be linked to a custom shortcut …
I never used anything else as a textfile in both directions.
And far from automated … 
Maybe Andrew has a solution / resource at hand that both of us aren’t aware of ?!
Regards,
CVH