Watch Files

A short feedback loop between writing code and seeing whether it compiles or passes tests is important for productive development. Your development environment can give you immediate feedback on syntax errors, but for running tests or rebuilding an application on every change, a file watcher is useful.

If you build web frontends in Rust using Trunk, file watching is built in: Trunk’s serve mode rebuilds and reloads your browser automatically on every change.

cargo-watch

cargo-watch is a tool you can use to watch your Rust projects and execute commands whenever a file changes.

You can install it using Cargo:

cargo install cargo-watch

By default, it will run cargo check when a change is detected:

# run `cargo check` whenever files change
cargo watch

You can customize it to run any command you like. Using the -x flag, you can tell it to run any other Cargo subcommand. You can also directly give it a command to run.

cargo watch -x test
cargo watch -- just test

It also supports command chaining, where you specify multiple Cargo subcommands to run. When doing so, it will run each of them in the order you specify them, when they are successful.

cargo watch -x check -x test -x run

The repository and help text explain more commands that you can use, such as specifying which files to watch.

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