improve bash syntax, mostly special char handling. #45

Job	Run time
run-tests (Windows 2015.03, windows-latest, https://files.openscad.org/OpenSCAD-2015.03-2-x86-64....	43s
Check code quality	4s
run-tests (MacOS 2015.03, macos-latest, https://files.openscad.org/OpenSCAD-2015.03-3.dmg, skip3m...	30s
run-tests (Ubuntu 2019.05, ubuntu-20.04, openscad=2019.05-3ubuntu5, old_boolean)	43s
run-tests (Windows 2019.05, windows-latest, https://files.openscad.org/OpenSCAD-2019.05-x86-64.zi...	1m 20s
run-tests (AppImage 2019.05, ubuntu-latest, https://files.openscad.org/OpenSCAD-2019.05-x86_64.Ap...	48s
run-tests (MacOS 2019.05, macos-latest, https://files.openscad.org/OpenSCAD-2019.05.dmg, old_bool...	1m 2s
run-tests (Ubuntu 2021.01, ubuntu-22.04, openscad=2021.01-4build1)	20s
run-tests (Windows 2021.01, windows-latest, https://files.openscad.org/OpenSCAD-2021.01-x86-64.zip)	1m 21s
run-tests (AppImage 2021.01, ubuntu-latest, https://files.openscad.org/OpenSCAD-2021.01-x86_64.Ap...	47s
run-tests (MacOS 2021.01, macos-latest, https://files.openscad.org/OpenSCAD-2021.01.dmg)	56s
run-tests (Ubuntu nightly, ubuntu-latest, https://files.openscad.org/OBS-Repository-Key.pub, http...	30s
run-tests (AppImage nightly, ubuntu-latest, https://files.openscad.org/snapshots/.snapshot_linux_...	1m 2s
run-tests (MacOS nightly, macos-latest, https://files.openscad.org/snapshots/.snapshot_macos.js)	1m 30s
run-tests (Windows nightly, windows-latest, https://files.openscad.org/snapshots/.snapshot_win64.js)	1m 17s
All tests passed	1s
	12m 54s

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