TIL: Auto-Running Commands on File Change With entr

Testing a script by running it manually after every edit is a waste of focus. entr watches files and runs a command when they change.

ls *.py | entr python test.py

Pipe the list of files to watch into entr. Every time a .py file changes, entr runs the test suite.

find . -name '*.js' | entr -c npm test

The -c flag clears the screen before each run. The output starts fresh every time.

ls server.js | entr -r node server.js

The -r flag sends a reload signal. If the command is a server, entr restarts it on file change. Like nodemon but for any command.

How do I install entr?

brew install entr

Does entr watch new files?

Only the files you pipe in initially. Add – to re-evaluate the command list, or use find with a cron-like approach.