How to hook the command window to capture output in real-time?

I need a way to hook the command window to capture output in real-time. Probably modify the java ui. I'd like whenever a line (errors included) is written to the command window, it would pass through my callback, and I'll send it to my log.

The motivation is viewing output when running a script from C++ API. I'm flying blind here, and my scripts may take hours. Current solutions such as diary, log file, or returned output from c++ eval() provide output only on completion.

This has been a long standing problem:

https://www.mathworks.com/matlabcentral/answers/140522-show-live-output-from-api?s_tid=prof_contriblnk

Currently, whenever I can, I use my own logger:

https://github.com/zoharl3/output_viewer

However, when calling external libs such as gurobi or ipopt, I don't have control. I could hook each one to write its own log file, but its a hassle.

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UPDATE

Considering the comments below, the post should be better named:

"How to capture C API output in real-time?"

Related post:

https://www.mathworks.com/matlabcentral/answers/52545-how-can-i-request-an-output-in-real-time-without-interrupting-my-program

[Walter Roberson]

If I recall correctly, diary() is specifically documented as flushing output no later than end-of-line... but the relevant documentation might be buried in release notes (that are no longer available online...)

[Zohar]

A correction: Diary flushes every line during an interactive session in the command window. However, it records nothing from the C API eval. Hooking the command window won't help me...