File Watching for Much Win
Throughout my career as a developer I’ve used lots of different file watching tools. It’s really handy to have something invoke your code every time you save the file. Some of them work well, but most do not. I recently discovered fswatch, and I couldn’t be happier.
fswatch is a binary you can install with homebrew. Just run brew install
fswatch. It’s a pretty low level tool, but using the right combination of
pipes and other unix commands, you can achieve pretty much any task you need
file watching for. I had quite a bit of trouble getting some of the flags
working that fswatch supports; perhaps I was misunderstanding how to use
them. Below are examples I’ve found to work flawlessly on my Mac.
Examples
fswatch *.go -l 0.2 | xargs -n1 go run
Watch all .go files in the current directory and go run them. The -n1
tells xargs to run for every new file name that gets piped to it. The -l
0.2 makes fswatch decrease the latency while watching. That number feels
right to be, but feel free to tweak it to your liking.
fswatch . -l 0.1 | egrep --line-buffered '\.(js)$' | xargs -n1 node
Recursively watch all .js files in the current directory and run them with
node.
fswatch . -l 0.1 | egrep --line-buffered '\.(js|jsx)$' | xargs -n1 -I{} echo "a javascript file was saved"
Recursively watch all .js or .jsx files in the current directory and echo
every time one is modified. The -I{} allows you to ignore the name of the
file that is piped to xargs. In this example we don’t care what specific file
was saved.