./shini.sh: line 49: syntax error: bad substitution

[dr-begemot]

I try you script on my system on arm, where I have only sh (not bash)

# sh ./example.sh 
./example.sh: ./shini.sh: line 49: syntax error: bad substitution

[wallyhall]

I fear that is likely because you're using BusyBox, which almost certainly hasn't been compiled with enough functionality.

I'll put this as a low-priority enhancement :-)

[Salvora]

same for me too with WSL ubuntu.

test.sh: 37: Bad substitution.

Calling with bash, no problem. I guess the problem is that shini is not posix compliant.