Run OpenSCAD module and capture ECHO output

Question

I have a chain of echo calls in my OpenSCAD model that generates some sort of Bill of Materials(BOM) that I would like to capture using command line.

Let's assume the model is valid and the syntax is correct. I would like to call it and get output rather than launching GUI.

How to do it?

OS is Linux
OpenSCAD version 2021.01 

Answer 1

I think I've found a workaround:

// echo argument must look like valid JSON string
echo(str("{\"support_plate_sqm\":", 0.37917, "}"));

# grep ECHO filters out all warnings, rendering time and other statics
#
# sed is a combination of 3 commands:
# (1) delete "ECHO: " prefix that we no longer need
# (2) and (3) remove unnecessary first and last double quote " so that output becomes valid jsonl
#
# jq is used as an example of an app that consumes valid jsonl output
openscad 000-000.scad -o $(mktemp).stl 2>&1 | grep ECHO | sed 's/ECHO: //;s/^.//;s/.$//' | jq -c '.support_plate_sqm'

Output:

0.37917

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