Description Jump to heading#

deno task provides a cross-platform way to define and execute custom commands specific to a codebase.

To get started, define your commands in your codebase's Deno configuration file under a "tasks" key.

For example:

{
  "tasks": {
    "data": "deno task collect && deno task analyze",
    "collect": "deno run --allow-read=. --allow-write=. scripts/collect.js",
    "analyze": {
      "description": "Run analysis script",
      "command": "deno run --allow-read=. scripts/analyze.js"
    }
  }
}

Running a task only if it exists Jump to heading#

deno task <name> exits with a non-zero code when the named task is not defined. To make a task optional, pass --if-present. Deno then exits with code 0 and prints nothing when the task is missing, which is useful for shared CI scripts that call a task only some packages define:

deno task --if-present build

The flag only suppresses the not-found case for the named task. Listing tasks with a bare deno task, running a task that does exist, and real errors such as a missing task dependency are unaffected.

Specifying the current working directory Jump to heading#

By default, deno task executes commands with the directory of the Deno configuration file (ex. deno.json) as the current working directory. This allows tasks to use relative paths and continue to work regardless of where in the directory tree you happen to execute the deno task from. In some scenarios, this may not be desired and this behavior can be overridden with the INIT_CWD environment variable.

INIT_CWD will be set with the full path to the directory the task was run in, if not already set. This aligns with the same behavior as npm run.

For example, the following task will change the current working directory of the task to be in the same directory the user ran the task from and then output the current working directory which is now that directory (remember, this works on Windows too because deno task is cross-platform).

{
  "tasks": {
    "my_task": "cd $INIT_CWD && pwd"
  }
}

Getting directory deno task was run from Jump to heading#

Since tasks are run using the directory of the Deno configuration file as the current working directory, it may be useful to know the directory the deno task was executed from instead. This is possible by using the INIT_CWD environment variable in a task or script launched from deno task (works the same way as in npm run, but in a cross-platform way).

For example, to provide this directory to a script in a task, do the following (note the directory is surrounded in double quotes to keep it as a single argument in case it contains spaces):

{
  "tasks": {
    "start": "deno run main.ts \"$INIT_CWD\""
  }
}

Wildcard matching of tasks Jump to heading#

The deno task command can run multiple tasks in parallel by passing a wildcard pattern. A wildcard pattern is specified with the * character.

{
  "tasks": {
    "build:client": "deno run -RW client/build.ts",
    "build:server": "deno run -RW server/build.ts"
  }
}

Running deno task "build:*" will run both build:client and build:server tasks.

For multi-word task names, we recommend using : as the separator (e.g. build:client, test:unit, lint:fix) to match the convention used in the npm ecosystem and to group related tasks for wildcard matching.

Exclude tasks from a wildcard match by adding an exclusion group (!a|b|c) to the end of the pattern. Each listed value is matched against what the * captured. For example, given test:unit, test:integration, test:e2e, and test:interactive tasks:

deno task "test:*(!e2e|interactive)"

runs test:unit and test:integration but skips test:e2e and test:interactive. A pattern that has an exclusion group but no * is rejected, since there is nothing to exclude from.

Loading environment variables from a file Jump to heading#

Pass --env-file to load variables from a dotenv file into the task's shell environment, so every command in the task body inherits them:

# Load .env
deno task --env-file start

# Load a specific file
deno task --env-file=.env.production start

The flag can be given more than once to load multiple files, with later files taking precedence. With no value it defaults to .env.

Task dependencies Jump to heading#

You can specify dependencies for a task:

{
  "tasks": {
    "build": "deno run -RW build.ts",
    "generate": "deno run -RW generate.ts",
    "serve": {
      "command": "deno run -RN server.ts",
      "dependencies": ["build", "generate"]
    }
  }
}

In the above example, running deno task serve will first execute build and generate tasks in parallel, and once both of them finish successfully the serve task will be executed:

deno task serve
Task build deno run -RW build.ts
Task generate deno run -RW generate.ts
Generating data...
Starting the build...
Build finished
Data generated
Task serve deno run -RN server.ts
Listening on http://localhost:8000/

Dependency tasks are executed in parallel, with the default parallel limit being equal to number of cores on your machine. To change this limit for a single invocation, pass --jobs (short -j, also spelled --concurrency); to set it for the environment, use the DENO_JOBS environment variable. The flag takes precedence:

# Run workspace tasks fully sequentially
deno task --recursive --jobs 1 build

Dependencies are tracked and if multiple tasks depend on the same task, that task will only be run once:

{
  //   a
  //  / \
  // b   c
  //  \ /
  //   d
  "tasks": {
    "a": {
      "command": "deno run a.js",
      "dependencies": ["b", "c"]
    },
    "b": {
      "command": "deno run b.js",
      "dependencies": ["d"]
    },
    "c": {
      "command": "deno run c.js",
      "dependencies": ["d"]
    },
    "d": "deno run d.js"
  }
}

deno task a
Task d deno run d.js
Running d
Task c deno run c.js
Running c
Task b deno run b.js
Running b
Task a deno run a.js
Running a

If a cycle between dependencies is discovered, an error will be returned:

{
  "tasks": {
    "a": {
      "command": "deno run a.js",
      "dependencies": ["b"]
    },
    "b": {
      "command": "deno run b.js",
      "dependencies": ["a"]
    }
  }
}

deno task a
Task cycle detected: a -> b -> a

You can also specify a task that has dependencies but no command. This is useful to logically group several tasks together:

{
  "tasks": {
    "dev:client": "deno run --watch client/mod.ts",
    "dev:server": "deno run --watch server/mod.ts",
    "dev": {
      "dependencies": ["dev:client", "dev:server"]
    }
  }
}

Running deno task dev will run both dev:client and dev:server in parallel.

Caching task results Jump to heading#

A task can skip work when none of its inputs have changed. Add a files field listing the input globs the task reads, and Deno fingerprints the command, its appended arguments, the contents of the matching files, and the values of any listed env vars, then skips the task on the next run when none of them changed. Caching is opt-in: a task with no files field always runs.

{
  "tasks": {
    "build": {
      "command": "deno run -RW build.ts",
      "files": ["src/**/*.ts", "deno.json"],
      "output": ["dist/"],
      "env": ["NODE_ENV"]
    }
  }
}

• files lists the input globs that make up the cache key. Declaring them is what turns on caching for the task.
• output lists the globs the task produces. On a cache hit they are restored from the cache, so deleting dist/ and re-running regenerates it.
• env lists environment variable names whose values are part of the cache key, so the task re-runs when one of them changes.

A task's dependency fingerprints are folded into its own cache key, so a task re-runs whenever an upstream one did.

Node and npx binary support Jump to heading#

By default, deno task will execute commands with the deno binary. If you need to ensure that a command is run with the npm or npx binary, you can do so by invoking the npm or npx run command respectively. For example:

{
  "tasks": {
    "test:node": "npm run test"
  }
}

Workspace support Jump to heading#

deno task can be used in workspaces, to run tasks from multiple member directories in parallel. To execute dev tasks from all workspace members use --recursive flag:

{
  "workspace": [
    "client",
    "server"
  ]
}

{
  "name": "@scope/client",
  "tasks": {
    "dev": "deno run -RN build.ts"
  }
}

{
  "name": "@scope/server",
  "tasks": {
    "dev": "deno run -RN server.ts"
  }
}

deno task --recursive dev
Task dev deno run -RN build.ts
Task dev deno run -RN server.ts
Bundling project...
Listening on http://localhost:8000/
Project bundled

Tasks to run can be filtered based on the workspace members:

deno task --filter "client" dev
Task dev deno run -RN build.ts
Bundling project...
Project bundled

Note that the filter matches against the workspace member names as specified in the name field of each member's deno.json file.

Syntax Jump to heading#

deno task uses a cross-platform shell that's a subset of sh/bash to execute defined tasks.

Boolean lists Jump to heading#

Boolean lists provide a way to execute additional commands based on the exit code of the initial command. They separate commands using the && and || operators.

The && operator provides a way to execute a command and if it succeeds (has an exit code of 0) it will execute the next command:

deno run --allow-read=. --allow-write=. collect.ts && deno run --allow-read=. analyze.ts

The || operator is the opposite. It provides a way to execute a command and only if it fails (has a non-zero exit code) it will execute the next command:

deno run --allow-read=. --allow-write=. collect.ts || deno run play_sad_music.ts

Sequential lists Jump to heading#

Sequential lists are similar to boolean lists, but execute regardless of whether the previous command in the list passed or failed. Commands are separated with a semi-colon (;).

deno run output_data.ts ; deno run --allow-net server.ts

Async commands Jump to heading#

Async commands provide a way to make a command execute asynchronously. This can be useful when starting multiple processes. To make a command asynchronous, add an & to the end of it. For example the following would execute sleep 1 && deno run --allow-net server.ts and deno run --allow-net client.ts at the same time:

sleep 1 && deno run --allow-net server.ts & deno run --allow-net client.ts

Unlike in most shells, the first async command to fail will cause all the other commands to fail immediately. In the example above, this would mean that if the server command fails then the client command will also fail and exit. You can opt out of this behavior by adding || true to the end of a command, which will force a 0 exit code. For example:

deno run --allow-net server.ts || true & deno run --allow-net client.ts || true

Environment variables Jump to heading#

Environment variables are defined like the following:

export VAR_NAME=value

Here's an example of using one in a task with shell variable substitution and then with it being exported as part of the environment of the spawned Deno process (note that in the JSON configuration file the double quotes would need to be escaped with backslashes):

export VAR=hello && echo $VAR && deno eval "console.log('Deno: ' + Deno.env.get('VAR'))"

Would output:

hello
Deno: hello

Setting environment variables for a command Jump to heading#

To specify environment variable(s) before a command, list them like so:

VAR=hello VAR2=bye deno run main.ts

This will use those environment variables specifically for the following command.

Shell variables Jump to heading#

Shell variables are similar to environment variables, but won't be exported to spawned commands. They are defined with the following syntax:

VAR_NAME=value

If we use a shell variable instead of an environment variable in a similar example to what's shown in the previous "Environment variables" section:

VAR=hello && echo $VAR && deno eval "console.log('Deno: ' + Deno.env.get('VAR'))"

We will get the following output:

hello
Deno: undefined

Shell variables can be useful when we want to reuse a value, but don't want it available in any spawned processes.

Exit status variable Jump to heading#

The exit code of the previously run command is available in the $? variable.

# outputs 10
deno eval 'Deno.exit(10)' || echo $?

Pipelines Jump to heading#

Pipelines provide a way to pipe the output of one command to another.

The following command pipes the stdout output "Hello" to the stdin of the spawned Deno process:

echo Hello | deno run main.ts

To pipe stdout and stderr, use |& instead:

deno eval 'console.log(1); console.error(2);' |& deno run main.ts

Command substitution Jump to heading#

The $(command) syntax provides a way to use the output of a command in other commands that get executed.

For example, to provide the output of getting the latest git revision to another command you could do the following:

deno run main.ts $(git rev-parse HEAD)

Another example using a shell variable:

REV=$(git rev-parse HEAD) && deno run main.ts $REV && echo $REV

Negate exit code Jump to heading#

To negate the exit code, add an exclamation point and space before a command:

# change the exit code from 1 to 0
! deno eval 'Deno.exit(1);'

Redirects Jump to heading#

Redirects provide a way to pipe stdout and/or stderr to a file.

For example, the following redirects stdout of deno run main.ts to a file called file.txt on the file system:

deno run main.ts > file.txt

To instead redirect stderr, use 2>:

deno run main.ts 2> file.txt

To redirect both stdout and stderr, use &>:

deno run main.ts &> file.txt

To append to a file, instead of overwriting an existing one, use two right angle brackets instead of one:

deno run main.ts >> file.txt

Suppressing either stdout, stderr, or both of a command is possible by redirecting to /dev/null. This works in a cross-platform way including on Windows.

# suppress stdout
deno run main.ts > /dev/null
# suppress stderr
deno run main.ts 2> /dev/null
# suppress both stdout and stderr
deno run main.ts &> /dev/null

Or redirecting stdout to stderr and vice-versa:

# redirect stdout to stderr
deno run main.ts >&2
# redirect stderr to stdout
deno run main.ts 2>&1

Input redirects are also supported:

# redirect file.txt to the stdin of gzip
gzip < file.txt

Note that redirecting multiple redirects is currently not supported.

Cross-platform shebang Jump to heading#

Starting in Deno 1.42, deno task will execute scripts that start with #!/usr/bin/env -S the same way on all platforms.

For example:

#!/usr/bin/env -S deno run
console.log("Hello there!");

{
  "tasks": {
    "hi": "./script.ts"
  }
}

Then on a Windows machine:

> pwd
C:\Users\david\dev\my_project
> deno task hi
Hello there!

Glob expansion Jump to heading#

Glob expansion is supported in Deno 1.34 and above. This allows for specifying globs to match files in a cross-platform way.

# match .ts files in the current and descendant directories
echo **/*.ts
# match .ts files in the current directory
echo *.ts
# match files that start with "data", have a single number, then end with .csv
echo data[0-9].csv

The supported glob characters are *, ?, and [/].

Shell options Jump to heading#

deno task supports shell options in Deno 2.6.6 and above to control glob expansion and pipeline behavior. By default, failglob and globstar are enabled.

• failglob - When enabled, globs that don't match any files will cause an error. Disable with shopt -u failglob.
• globstar - When enabled, ** matches zero or more directories. Disable with shopt -u globstar.
• nullglob - When enabled, globs that don't match any files expand to nothing instead of the literal glob pattern. Enable with shopt -s nullglob.
• pipefail - When enabled, the exit code of a pipeline is the exit code of the last command to exit with a non-zero status, or zero if all commands exit successfully. Enable with set -o pipefail.
• errexit (Deno 2.8+) - When enabled, a sequential list aborts on the first command that exits non-zero. Enable with set -e or set -o errexit; disable again with set +e or set +o errexit. Useful when porting a shell script that relies on set -e semantics into a tasks block.

Examples:

{
  "tasks": {
    // disable failglob
    "task1": "shopt -u failglob && rm -rf *.ts",
    // disable failglob and enable nullglob
    "task2": "shopt -u failglob && shopt -s nullglob && rm -rf *.ts",
    // disable globstar
    "task3": "shopt -u globstar && echo **/*.ts",
    // enable pipefail
    "task4": "set -o pipefail && cat missing.txt | echo 'hello'",
    // abort the sequential list on the first failing command
    "task5": "set -e; build_step_one; build_step_two; build_step_three"
  }
}

Built-in commands Jump to heading#

deno task ships with several built-in commands that work the same out of the box on Windows, Mac, and Linux.

• cp - Copies files.
• mv - Moves files.
• rm - Remove files or directories.
  • Ex: rm -rf [FILE]... - Commonly used to recursively delete files or directories.
• mkdir - Makes directories.
  • Ex. mkdir -p DIRECTORY... - Commonly used to make a directory and all its parents with no error if it exists.
• pwd - Prints the name of the current/working directory.
• sleep - Delays for a specified amount of time.
  • Ex. sleep 1 to sleep for 1 second, sleep 0.5 to sleep for half a second, or sleep 1m to sleep a minute
• echo - Displays a line of text.
• cat - Concatenates files and outputs them on stdout. When no arguments are provided it reads and outputs stdin.
• exit - Causes the shell to exit.
• head - Output the first part of a file.
• export - Sets environment variables and exports them to spawned commands.
• unset - Unsets environment variables.
• xargs - Builds arguments from stdin and executes a command.
• : - The POSIX null command. Does nothing and always exits with status 0 (Deno 2.8+). Handy as a no-op placeholder in conditionals or for parameter-expansion side effects.

If you find a useful flag missing on a command or have any suggestions for additional commands that should be supported out of the box, then please open an issue on the deno_task_shell repo.

Note that if you wish to execute any of these commands in a non-cross-platform way on Mac or Linux, then you may do so by running it through sh: sh -c <command> (ex. sh -c cp source destination).

package.json support Jump to heading#

deno task falls back to reading from the "scripts" entries in a package.json file if it is discovered. Note that Deno does not respect or support any npm life cycle events like preinstall or postinstall—you must explicitly run the script entries you want to run (ex. deno install --entrypoint main.ts && deno task postinstall).

When deno task runs a package.json script, it sets the npm_* environment variables that npm exposes, so scripts that read them keep working. These include npm_package_name, npm_package_version, npm_lifecycle_event (the script name), npm_lifecycle_script (its command string), and npm_config_user_agent, along with npm_execpath and npm_node_execpath (both set to the path of the running deno executable) and npm_command (set to run-script). These variables are set only for package.json scripts. Tasks defined in deno.json do not receive them.

Command Resolution Jump to heading#

When a task command references a binary (e.g., ohm, tsc, eslint), Deno resolves it using the following order:

1. node_modules/.bin/ - if the task's directory or a parent directory has a node_modules/.bin/ folder, Deno looks there first. Note that deno add npm:<pkg> updates deno.json imports and deno.lock but does not create a node_modules directory. The node_modules directory is only created when using deno install or other npm-compatible tooling.

2. package.json bin field - when a dependency defines a bin field in its package.json, Deno automatically makes those commands available within task scripts through its npm compatibility layer.

3. System PATH - if the command is not found above, Deno falls back to searching the system PATH.

Example Jump to heading#

Given a package.json with:

{
  "dependencies": {
    "@ohm-js/cli": "^2.0.0"
  }
}

And a deno.json with:

{
  "tasks": {
    "generate": "ohm src/grammar.ohm -o src/grammar.js"
  }
}

Running deno task generate will:

1. Look for ohm in node_modules/.bin/ohm
2. If found, execute it using Deno's Node.js compatibility layer
3. The command runs under Deno's runtime, not Node.js.

deno task [OPTIONS] [TASK]

deno task build

deno task

deno task --eval "echo $(pwd)"