Earlier quoted context omitted.
#!/bin/sh Leave bash out of it tbh. In practice that will often end up being bash, but sometimes it won't be an in those cases you'll have yourself covered. Test it with busybox's sh or with dash, just to make sure.
I disagree. I have seen developpers trying to write posix conformant scripts but only testing on bash on redhat. When deploying on ubuntu, /bin/sh was dash and the script did not work. I think people shall use #!/bin/bash until their script has been really tested using dash or busybox. If they do not want to do this additional test work, they should never use #!/bin/sh
It's really not that difficult to avoid bashisms if you get yourself into the habit now, rather than later.