Command Line Interface
Deno is a command line program. You should be familiar with some simple commands having followed the examples thus far and already understand the basics of shell usage.
There are multiple ways of viewing the main help text:
# Using the subcommand.
# Using the short flag -- outputs the same as above.
# Using the long flag -- outputs more detailed help text where available.
Deno's CLI is subcommand-based. The above commands should show you a list of
subcommands supported, such as
deno compile. To see subcommand-specific help,
for example for
compile, you can similarly run one of:
deno help compile
deno compile -h
deno compile --help
Detailed guides for each subcommand can be found here.
Deno can grab the scripts from multiple sources, a filename, a url, and '-' to read the file from stdin. The latter is useful for integration with other applications.
deno run main.ts
deno run https://mydomain.com/main.ts
cat main.ts | deno run -
Separately from the Deno runtime flags, you can pass user-space arguments to the script you are running by specifying them after the script name:
deno run main.ts a b -c --quiet
console.log(Deno.args); // [ "a", "b", "-c", "--quiet" ]
Note that anything passed after the script name will be passed as a script argument and not consumed as a Deno runtime flag. This leads to the following pitfall:
# Good. We grant net permission to net_client.ts.
deno run --allow-net net_client.ts
# Bad! --allow-net was passed to Deno.args, throws a net permission error.
deno run net_client.ts --allow-net
Some see it as unconventional that:
a non-positional flag is parsed differently depending on its position.
- This is the most logical and ergonomic way of distinguishing between runtime flags and script arguments.
- This is, in fact, the same behaviour as that of any other popular runtime.
node -c index.jsand
node index.js -c. The first will only do a syntax check on
index.jsas per Node's
-cflag. The second will execute
There exist logical groups of flags that are shared between related subcommands. We discuss these below.
You can supply the
--watch flag to
deno fmt to enable the built-in file watcher. The files that are watched
depend on the subcommand used:
deno test, and
deno compilethe entrypoint, and all local files the entrypoint(s) statically import(s) will be watched.
deno fmtall local files and directories specified as command line arguments (or the working directory if no specific files/directories is passed) are watched.
Whenever one of the watched files is changed on disk, the program will automatically be restarted / formatted / tested / bundled.
deno run --watch main.ts
deno test --watch
deno fmt --watch
Integrity flags (lock files)
Affect commands which can download resources to the cache:
deno doc, and
--lock <FILE> Check the specified lock file
--lock-write Write lock file. Use with --lock.
Find out more about these here.
Cache and compilation flags
Affect commands which can populate the cache:
deno doc, and
deno compile. As well as the flags above, this
includes those which affect module resolution, compilation configuration etc.
--config <FILE> Load configuration file
--import-map <FILE> Load import map file
--no-remote Do not resolve remote modules
--reload=<CACHE_BLOCKLIST> Reload source code cache (recompile TypeScript)
--unstable Enable unstable APIs
Affect commands which execute user code:
deno run and
deno test. These
include all of the above as well as the following.
Type checking flags
You can type-check your code (without executing it) using the command:
> deno check main.ts
You can also type-check your code before execution by using the
argument to deno run:
> deno run --check main.ts
This flag affects
deno repl and
deno cache. The
following table describes the type-checking behavior of various subcommands.
Here "Local" means that only errors from local code will induce type-errors,
modules imported from https URLs (remote) may have type errors that are not
reported. (To turn on type-checking for all modules, use
|Subcommand||Type checking mode|
These are listed here.
Other runtime flags
More flags which affect the execution environment.
--cached-only Require that remote dependencies are already cached
--inspect=<HOST:PORT> activate inspector on host:port ...
--inspect-brk=<HOST:PORT> activate inspector on host:port and break at ...
--inspect-wait=<HOST:PORT> activate inspector on host:port and wait for ...
--location <HREF> Value of 'globalThis.location' used by some web APIs
--prompt Fallback to prompt if required permission wasn't passed
--seed <NUMBER> Seed Math.random()
--v8-flags=<v8-flags> Set V8 command line options. For help: ...
You can get IDE-style autocompletions for Deno with Fig. It works in bash, zsh, and fish.
To install, run:
brew install fig