A collection of dos and don’ts for writing bash scripts: https://github.com/azet/community_bash_style_guide.

Some tips are not bash-specific, but are about external commands usable with any shell: e.g. awk, sed, grep, pgrep, xargs. Also some builtins should be available with any POSIX-compliant shell, e.g. getopts, printf.

Most surprising bit of information: that someone has written a “ctypes” (foreign-function interface) addon for bash https://github.com/taviso/ctypes.sh.