Cargo Watch watches over your project's source for changes, and runs Cargo commands when they occur.
If you've used nodemon, gulp, guard, watchman, or similar others, it will probably feel familiar.
Pre-built binaries are available on the Github Releases tab.
$ cargo install cargo-watch
To upgrade:
$ cargo install --force cargo-watch
Or clone and build with $ cargo build
then place in your $PATH.
By default, it runs check
(which is available since Rust 1.16).
You can easily override this, though:
$ cargo watch [-x command]...
A few examples:
# 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 -s 'echo Hello world'
There's a lot more you can do! Here's a copy of the help:
USAGE:
cargo watch [FLAGS] [OPTIONS]
FLAGS:
-c, --clear Clear the screen before each run
--debug Display debug output
-h, --help Display this message
--ignore-nothing Ignore nothing, not even target/ and .git/
--no-gitignore Don’t use .gitignore files
--no-restart Don’t restart command while it’s still running
--poll Force use of polling for file changes
--postpone Postpone first run until a file changes
-q, --quiet Suppress output from cargo-watch itself
-V, --version Display version information
OPTIONS:
-x, --exec <cmd>...
Cargo command(s) to execute on changes [default: check]
-s, --shell <cmd>...
Shell command(s) to execute on changes
-d, --delay <delay>
File updates debounce delay in seconds [default: 0.5]
-i, --ignore <pattern>...
Ignore a glob/gitignore-style pattern
-w, --watch <watch>...
Watch specific file(s) or folder(s) [default: .]
Cargo commands (-x) are always executed before shell commands (-s).
By default, your entire project is watched, except for the target/
and .git/ folders, and your .gitignore files are used to filter paths.
See the glob::Pattern
docs 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.
From Cargo Watch 7.0.0, /
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.
Cargo Watch pairs very well with Catflap, a tool for Unixy platforms that lets one spawn a socket before the watcher runs that Rust servers can then bind to, avoiding request-dropping and the infamous ADDRINUSE error. For example:
$ catflap -- cargo watch -x run
Of course, if you don't need to guard against these issues or don't want to modify your program to grab sockets instead of ports, you can use Cargo Watch as-is: it will happily just restart your server normally.
Brought up by @LeDominik, here's a pattern that may be very useful: you're working on a server or app, but want it to keep running while you're writing a new feature or fixing a bug, potentially causing the code not to compile anymore in the meantime.
In this case, you can use this strategy: run a first cargo watch
with check,
build, test, or whatever you want, and append -s 'touch .trigger
(or equivalent
for your platform). Then, run a second cargo watch
simultaneously that only
watches that .trigger
file. For example:
$ cargo watch -x check -s 'touch .trigger'
and
$ cargo watch --no-gitignore -w .trigger -x run`
The --no-gitignore
flag ensures that you can safely add .trigger
to your
.gitignore
file to avoid mistakenly committing it.
The Cargo Watch team enthusiastically welcomes contributions and project participation! There's a bunch of things you can do if you want to contribute! The Contributor Guide has all the information you need for everything from reporting bugs to contributing entire new features. Please don't hesitate to jump in if you'd like to, or even ask us questions if something isn't clear. {attribution}
You can also contribute financially with Ko-fi or Patreon.
In all cases, start by checking your version with cargo watch --version
and,
if necessary, upgrading to the latest one.
Cargo Watch versions 5.0.0 and up (and watchexec versions 1.3.0 and up) do not support Windows 7 or lower. There are no plans at the moment to add such support.
You can downgrade to the last version which did support Windows 7 (and lower), but do keep in mind that many bug fixes and features are missing there:
$ cargo install --force --vers 4.0.3 cargo-watch
You're probably using version 4 (or higher) but using the version 3 (or lower) style of arguments. The interface changed! Refer to the sections above for new usage guidelines, or to the help message:
$ cargo watch --help
You can! But you'll have to specify the watch
subcommand as the first
argument, like so:
$ /path/to/cargo-watch watch -x build
That's not supported. If you have a good reason to use a Cargo-specific tool outside a Cargo project, please open an issue! Otherwise, you'll probably be best served with using Watchexec.
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.
You may have hit the inotify watch limit. Here's a summary of what this means and how to increase it.
Cargo workspaces are not natively supported yet.
However, as you can run "arbitrary commands" with the -s
option, you can
write workspace-aware commands manually.
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.
Make sure the files you ignored are the only ones being touched. Use the
--debug
option to see exactly which files were modified and triggered the
restart (or were ignored). Some programs and libraries create temporary files
that may not match a simple ignore pattern.
Please open an issue, or look through the existing ones. You may also want to look through issues for the Notify library this tool depends on, or the issues for the Watchexec tool that we use under the covers.
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.
You cannot do that directly. You may of course call cargo-watch
as any other
program, but if you want to directly / statically embed it, that's not
possible. But! Cargo Watch is built on top of Watchexec, Watchexec is itself
built on Notify, and both of these can be used as Rust libraries.
-
If you want to build a tool that runs, restarts, and otherwise manages commands in response to file changes, you'll most probably want to use Watchexec.
-
If you want to build a tool that responds to file changes, but does not need to run commands, or does so in a way that is not well-supported by Watchexec, then Notify is your ticket.
It is! Watchexec does a really good job of watching files and running commands
and all the details that go with this. Cargo watch simply embeds watchexec and
calls it with its own custom options and defaults, so you can just run
cargo-watch
in your project and be in business.
Created by Félix Saparelli and awesome contributors.