CARGO-WATCH(1)

📦
version 8.5.3 · 2 versions
, in alpine 3.24

🎀 NAME 🎀

Okay so bestie, welcome to the CARGO-WATCH(1) manual page 💖. The name is cargo-watch, and it watches over your Cargo project's source. It's giving “your personal build-watch gremlin” energy, and honestly? Iconic. It ate and left no crumbs. ✨

🦋 SYNOPSIS 🦋

Here's the invocation vibe, copied exactly so we don't mess with the syntax:

cargo watch [options] [--exec | -x cargo subcommand]... [--shell | -s
command]... [-- command...] cargo watch [--version | -V] cargo watch
[--help | -h]

✨ DESCRIPTION ✨

Okay so lowkey the whole point is: it watches over your project's source for changes, and runs Cargo commands when they occur. Highkey a vibe. No cap: it's your “something changed, do the thing” bestie. 🔥

🧚 COMMANDS 🧚

Commands are main character energy here, so let's meet them.

💅 cargo subcommand

Cargo subcommand to run when watched files are modified, and at startup, unless --postpone is specified.

This is essentially the same as <command> but with cargo prepended, except that in addition, cargo-specific options are applied, such as --features.

🫶 command

Command to run when watched files are modified, and at startup, unless --postpone is specified.

All commands passed are joined together with &&.

Cargo commands (-x) are always executed before shell commands (-s).

If a trailing command is given with -- <command>, it supersedes all other commands.

🌈 OPTIONS 🌈

Okay bestie, here's the whole flag menu — no skips, periodt. iykyk. Not me being obsessed with a flag list, but here we are. 💅

  • -h, --help — Display this message.
  • -V, --version — Display version information.
  • --debug — Show debug output.
  • --why — Show paths that changed.
  • -q, --quiet — Suppress output from cargo-watch itself.
  • --skip-local-deps — Don't try to find local dependencies of the current crate and watch their working directories. Only watch the current directory.
  • -w, --watch watch... — Watch specific file(s) or folder(s). Disables finding and watching local dependencies. By default, the workspace directories of your project and all local dependencies are watched, except for the target/ and .git/ folders. Your .ignore and .gitignore files are used to filter paths.
  • -i, --ignore pattern... — Ignore a glob/gitignore-style pattern. On Windows, patterns given to -i have forward slashes (/) automatically converted to backward ones (\) to ease command portability.
  • --no-vcs-ignores — Don't use .gitignore files.
  • --no-dot-ignores — Don't use .ignore files.
  • --ignore-nothing — Ignore nothing, not even target/ and .git/.
  • -c, --clear — Clear the screen before each run.
  • -E, --env-var key=value — Inject an environment variable.
  • --env-file path — Inject environment variables from a dotenv-style file.
  • -B value — Inject RUST_BACKTRACE=<value> into the environment. This is useful when panics are handled and you want a backtrace to be printed: usually you'd have to add RUST_BACKTRACE=1 yourself, this shortens it to -B1!
  • -L value — Inject RUST_LOG=<value> into the environment.
  • --experimental--env-changes — Unstable option which will set WATCHEXEC_* environment variables on the command to gather information on the files changes cargo watch saw. Do not rely on this, may disappear or change without notice. Note that the files listed are not guaranteed to be the full list of files changed, nor indeed to even have been changed at all, and that this may vary between platforms. In general, finding the list of files that changed is best done by other tools such as find, to list out all the files with a modification date greater than the last known execution.
  • -C, --workdir path — Change the working directory to the path given. The default is the crate root, as found by cargo locate-project.
  • --postpone — Postpone first run until a file changes.
  • --poll — Force use of polling for file changes.
  • --no-process-group — By default, Cargo Watch uses a process group to run the command(s). This disables that behaviour.
  • -d, --delay delay — File updates debounce delay in seconds (default: 0.5).
  • --no-restart — Don't restart command while it's still running.
  • --watch-when-idle — Ignore events emitted while the commands run.
  • --features features — List of features passed to cargo invocations. The features will be passed to every supported cargo subcommand. For example, with this command: $ cargo watch --features foo,bar -x clean -x build -x doc Both build and doc will be run with the foo and bar features, but clean won't.
  • --use-shell use-shell — Use a different shell. E.g. --use-shell=bash. On Windows, try --use-shell=powershell. The special value none will use no shell, but will only work with a trailing command, not -x or -s.

🍓 EXAMPLES 🍓

Okay, here's the vibe check: run cargo check on file save:

$ cargo watch

Run tests only:

$ cargo watch -x test

Run check then tests:

$ cargo watch -x check -x test

Run run with arguments:

$ cargo watch -x ´run -- --some-arg´

Run an arbitrary command:

$ cargo watch -- echo Hello world

Run with features passed to cargo:

$ cargo watch --features ´foo,bar´

🌸 DETAILS 🌸

🦋 Ignore files 🦋

This is where the ignore lore lives.

.gitignore files are used by default to ignore paths to watch and trigger runs. To stop honouring them, pass --no-vcs-ignores.

.ignore files in the same syntax are also used by default. This file can be used to specify files that should be ignored by cargo watch but checked into git, without constantly adding --ignore abc options on the command-line. Do note that .ignore files may also be used by other programs, like ripgrep(1). To stop honouring these, pass --no-dot-ignores.

Cargo watch also has an internal list of default ignores on top of those specified in files, like target/ and .git/ and various other common types (logs, editor swap files, lockfiles, etc).

To skip literally all ignores, use the --ignore-nothing flag.

🧚 Ignore syntax 🧚

See the glob::Pattern docs0 https://doc.rust-lang.org/glob/glob/struct.Pattern.html for a more detailed specification of the glob matching syntax used for --ignore.

On Windows, patterns should be specified with Windows-style (\\) separators. Unix-style separators (/) would not match Windows paths, which could be confusing and give the appearance of commandline ignores not working. For convenience / in commandline ignores are automatically translated to \\ when running on Windows, but one should still try to write the correct patterns for the platform, as there may be more subtle differences.

💀 BUGS 💀

Bugs happen, bestie — fr fr.

Please open an issue1 https://github.com/watchexec/cargo-watch/issues, or look through the existing ones.

If you want more verbose output, try running with the --debug flag. Note that this will also enable debug mode for watchexec. When filing an issue, make sure to include a log with --debug enabled so problems can be diagnosed, as well as your --version and OS.

If your issue is a watchexec (our main upstream) issue, open it there2 https://github.com/watchexec/watchexec/issues directly. If you're not sure, feel free to open it on the cargo-watch issue tracker, but if it is a watchexec issue, it will be transferred over anyway.

🐛 KNOWN BUGS 🐛

In 7.8.0, the --workdir option changes the directory before any other options are processed, so e.g. --watch paths may not work as expected. This is fixed upstream in Watchexec library 2.

In 8.x, the -B, -L, -E, --env-var, --env-file options inject environment variables into the main cargo-watch process, which may be unsound in some situations and may also affect cargo-watch itself. This is fixed upstream in Watchexec library 2.

🧚 TROUBLESHOOTING 🧚

If something's acting up, start here.

Always start by checking your version with cargo watch --version and, if necessary, upgrading to the latest one by checking the website linked above.

😭 RLS is slow while using cargo watch, or vice versa, or it´s waiting for the project lock a lot 😭

Cargo builds (and checks, and clippy, and tests because the tests have to be built) take out a lock on the project so two cargo instances don't run at the same time.

However, Rust Analyzer is much better at this, so use that instead of RLS.

🙈 File updates seems to never trigger 🙈

Try using --poll to force the polling fallback.

If that still doesn't work, and you're using an editor that does "safe saving", like IntelliJ / PyCharm, you may have to disable "safe saving" as that may prevent file notifications from being generated properly.

Also try using the --why option to see if the paths you expect are changing.

💀 It runs repeatedly without touching anything 💀

That can happen when watching files that are modified by the command you're running.

If you're only running compiles or checks (i.e. any command that only affects the target/ folder) and you're using -w, you might be confusing the target-folder-ignorer. Check your options and paths.

You can also use the --watch-when-idle flag to ignore any event that happens while the command is running. This will become the default in 8.0.

🌸 It runs repeatedly only touching ignored files 🌸

Make sure the files you ignored are the only ones being touched. Use the --why option to see exactly which files were modified and triggered the restart. Some programs and libraries create temporary files that may not match a simple ignore pattern.

As above, you can also use the --watch-when-idle flag to help.

🎀 I don´t have colour in my cargo output / for cargo test 🎀

This sometimes happens on some terminal configurations or for test harnesses. A quick workaround (instead of going down the rabbit hole of debugging your console settings) is to pass --color=always to the command. E.g.

$ cargo watch -x ´check --color=always´

For test (and bench) commands, you'll need to pass the flag to the underlying program instead of cargo:

$ cargo watch -x ´test -- --color=always´

💜 AUTHOR 💜

Written and maintained by Félix Saparelli.

https://passcod.name

Project homepage:

https://watchexec.github.io/#cargo-watch

Public domain.

🍓 Sign-off: that's the CARGO-WATCH(1) manual page, January 2024, and it's public domain. Bye bestie, go slay those builds! 🍓

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