Agnostic livereload with Entr

Entr overview

Today, I would like to introduce you to the project entr. I discovered this project randomly a while ago, but I had been searching for a tool like this for a while.

The goal of this tool is to provide a simple command which can launch a specified command when some files are modified. Concretely, this tool can be useful if you are searching for an alternative to livereload, but not related to a specific language and not related to a full blown IDE

Example

I often use it to automatically launch tests for Golang projects I am developping.

Imagine, I wish to test the following function in the pkg.go file:

// Inc returns the op1 integer incremented by one unit
func Inc(op1 int) int {
	return op1 + 1
}

I wish to test it, with this test in pkg_test.go:

func Test_Inc(t *testing.T) {
	actual := Inc(1)
	if actual != 2 {
		t.Errorf("Expecting: <2>, got <%d>", actual)
	}
}

I would launch my tests continuously with the following command:

find *.go | entr -c -s "go test ."

Here is a live preview of the result (using asciinema):

At first, the test is not working, but as soon as the test file is updated, the test is launched again. The specificity here, is to use the -c flag, in order to clear the screen before launching the new command.

You can find the full list of options here

How does it work ?

In order to avoid polling, entr uses file system events (kqueue with BSD, inotify with Linux).

How to get it ?

If you wish to install it, it’s really easy, just use your Linux distribution package:

Ubuntu, Debian, Mint, … :

$ apt install entr

Centos, … :

$ yum install entr

MacOS :

$ brew install entr