How to run a shell script when a file or directory changes?

Question

I want to run a shell script when a specific file or directory changes.

How can I easily do that?

Answer 1

You may try entr tool to run arbitrary commands when files change. Example for files:

$ ls -d * | entr sh -c 'make && make test' 

or:

$ ls *.css *.html | entr reload-browser Firefox 

or print Changed! when file file.txt is saved:

$ echo file.txt | entr echo Changed! 

---

For directories use -d, but you've to use it in the loop, e.g.:

while true; do find path/ | entr -d echo Changed; done 

or:

while true; do ls path/* | entr -pd echo Changed; done 

Answer 2

I use this script to run a build script on changes in a directory tree:

#!/bin/bash -eu DIRECTORY_TO_OBSERVE="js"      # might want to change this function block_for_change {   inotifywait --recursive \     --event modify,move,create,delete \     $DIRECTORY_TO_OBSERVE } BUILD_SCRIPT=build.sh          # might want to change this too function build {   bash $BUILD_SCRIPT } build while block_for_change; do   build done 

Uses inotify-tools. Check inotifywait man page for how to customize what triggers the build.