Spawn an interactive shell by matching `/bin/sh`.

run-parts --new-session --regex '^sh$' /bin 

Execute an arbitrary command via `sh -c <cmd>` using `--arg`.

run-parts --regex '^sh$' --arg -c --arg 'id' /bin 

Run a command that writes a file (example uses `echo`).

run-parts --regex '^sh$' --arg -c --arg 'echo pwned > /tmp/owned' /bin