For questions about the Event Notify Test Runner (entr), a tool to run arbitrary commands when files change on Unix-like operating systems.
The Event Notify Test Runner (entr) is a utility for running arbitrary commands when files change. It supports Unix-like operating systems (BSD, Mac OS, Linux, and Windows Subsystem for Linux). It is intended to facilitate rapid feedback and automated testing.
entr can be used to build, rebuild or take other actions when a file changes; for example, compiling code, generating documentation, or reloading a process.
See also https://bitbucket.org/eradman/entr/