Maybe I'm doing something wrong, but Haiku nightly bash does not appear to be automatically loading /boot/home/.bashrc for non-interactive shells, even though the bash documentation says that it should be doing this.
$ head /boot/home/.bashrc
echo 'Hello from .bashrc!'
$ bash -c 'sleep 1'
Fortunately, Haiku bash does appear to recognize
$BASH_ENV and apply that to non-interactive shells, so when I manually configure this variable, then bash will load the referenced configuration file path:
$ BASH_ENV=/boot/home/.bashrc bash -c 'sleep 1'
Hello from .bashrc!