As a developer there are many occasions where you are editing some files and executing the same commands over and over again. For example when I’m writing code I like to frequently run my unit tests to make sure that everything still works as expected. I quickly end in the following loop:
$ vim app.py # Making some changes to the source code
$ pytest # Running the tests
$ vim app.py # More changes
This quickly becomes a drag and we might want to run our tests as soon as our source code changes.
entr is a small tool that allows you to run arbitrary commands as soon as some files change.
Automating the scenario above is as simple as executing the following command
$ find . -type f -path '*.py' | entr pytest
As soon as I save one of my source files entr will make sure my tests are executed.
As entr takes it’s input from
STDIN you can easily use it for a variety of tasks. The following examples can be found in the man pages:
Launch and auto-reload a node.js server:
$ ls *.js | entr -r node app.js
Clear the screen and run a query after the SQL has been updated:
$ echo my.sql | entr -cp psql /_
Other examples can be found on the website of entr