Using entr to react to file changes

entr is "A utility for running arbitrary commands when files change". It's available on both Linux and MacOS.

# Run make build when source files change
find . -type f -name '*.c' | entr make build

/_ is a shorthand that is replaced with the absolute path of the first file to trigger an event.

# Run my_script.sh on save
echo my_script.sh | entr /_