How to automatically execute a shell command after saving a file in Vim?

This runs run_tests.sh after any file is saved, with the current filename as the only parameter:

:autocmd BufWritePost * !run_tests.sh <afile>

View the auto-command with:

:autocmd BufWritePost *

And remove all auto-commands from the previous with:

:autocmd! BufWritePost *