A normalised way to handle CLI arguments and password handling via a set of available options.
Input are treated as streams.
Report progress via SIGINFO and spit out some statistic or diagnostic message.
My tools generally produce line-based output on stdout, as you would expect. If the output consists of multiple fields, it is either space- or comma separated; or JSON because the processing is easy with jq.

Temporary files can be used, but securely: https://www.netmeister.org/blog/mktemp.html