docs/versioned_docs/version-0.16.3/api/arguments.mdx
import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';
Dagger Functions, just like regular functions, can accept arguments. In addition to basic types (string, boolean, integer, arrays...), Dagger also defines powerful core types which Dagger Functions can use for their arguments, such as Directory, Container, Service, Secret, and many more.
When calling a Dagger Function from the CLI, its arguments are exposed as command-line flags. How the flag is interpreted depends on the argument type.
:::important Dagger Functions execute in containers and thus do not have default access to your host environment (host files, directories, environment variables, etc.). Access to these host resources can only be granted by explicitly passing them as argument values to the Dagger Function.
File or Directory. Pass files and directories on your host by specifying their path as the value of the argument when using dagger call.$ENV_VAR_NAME when using dagger call.Service can be passed local network services in the form tcp://HOST:PORT.
:::To pass a string argument to a Dagger Function, add the corresponding flag to the dagger call command, followed by the string value.
Here is an example of a Dagger Function that accepts a string argument:
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-string/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-string/python/main.py ```Even though the Python runtime doesn't enforce type annotations at runtime, it's important to define them with Dagger Functions. The Python SDK needs the typing information at runtime to correctly report to the API. It can't rely on type inference, which is only possible for external static type checkers.
If a function doesn't have a return type annotation, it'll be declared as None,
which translates to the dagger.Void type in the API:
@function
def hello(self):
return "Hello world!"
# Error: cannot convert string to Void
It's fine however, when no value actually needs to be returned:
@function
def hello(self):
...
# no return
Even though PHP doesn't enforce type annotations at runtime, it's important to define them with Dagger Functions. The PHP SDK needs the typing information at runtime to correctly report to the API.
</TabItem> <TabItem value="Java"> ```java file=./snippets/functions/arguments-string/java/src/main/java/io/dagger/modules/mymodule/MyModule.java ``` </TabItem> </Tabs>Here is an example call for this Dagger Function:
dagger call get-user --gender=male
The result will look something like this:
{
"title": "Mr",
"first": "Hans-Werner",
"last": "Thielen"
}
To pass host environment variables as arguments when invoking a Dagger Function, use the standard shell convention of $ENV_VAR_NAME when using dagger call.
Here is an example of passing a host environment variable containing a string value to a Dagger Function:
export GREETING=bonjour
dagger -m github.com/shykes/daggerverse/[email protected] call hello --greeting=$GREETING
To pass a Boolean argument to a Dagger Function, simply add the corresponding flag, like so:
--foo=true, or simply --foo--foo=falseHere is an example of a Dagger Function that accepts a Boolean argument:
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-boolean/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-boolean/python/main.py ``` </TabItem> <TabItem value="TypeScript"> ```typescript file=./snippets/functions/arguments-boolean/typescript/index.ts ``` </TabItem> <TabItem value="PHP"> ```php file=./snippets/functions/arguments-boolean/php/src/MyModule.php ``` </TabItem> <TabItem value="Java"> :::note You can either use the primitive `boolean` type or the boxed `java.lang.Boolean` type. :::Here is an example call for this Dagger Function:
dagger call hello --shout=true
The result will look like this:
HELLO, WORLD
To pass an integer argument to a Dagger function, add the corresponding flag to the dagger call command, followed by the integer value.
Here is an example of a Dagger function that accepts an integer argument:
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-return-values-integer/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-return-values-integer/python/main.py ``` </TabItem> <TabItem value="TypeScript"> ```typescript file=./snippets/functions/arguments-return-values-integer/typescript/index.ts ``` </TabItem> <TabItem value="PHP"> ```php file=./snippets/functions/arguments-return-values-integer/php/src/MyModule.php ``` </TabItem> <TabItem value="Java"> :::note You can either use the primitive `int` type or the boxed `java.lang.Integer` type. :::Here is an example call for this Dagger Function:
dagger call add-integer --a 1 --b 2
The result will look like this:
3
To pass a floating-point number as argument to a Dagger function, add the corresponding flag to the dagger call command, followed by the value.
Here is an example of a Dagger function that accepts a floating-point number as argument:
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-return-values-float/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-return-values-float/python/main.py ``` </TabItem> <TabItem value="TypeScript">:::note
There's no float type keyword in TypeScript because the type keyword number already supports floating point numbers.
To declare a float argument on the function signature, import float from @dagger.io/dagger and use it as an argument's type.
The imported float type is a number underneath, so you can use it as you would use a number inside your function.
:::
Here is an example call for this Dagger Function:
dagger call add-float --a 1.4 --b 2.7
The result will look like this:
4.1
To pass an array argument to a Dagger Function, add the corresponding flag, followed by a comma-separated list of values.
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-array/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-array/python/main.py ``` </TabItem> <TabItem value="TypeScript"> ```typescript file=./snippets/functions/arguments-array/typescript/index.ts ``` </TabItem> <TabItem value="PHP"> :::note Lists must have their subtype specified by adding the `#[ListOfType]` attribute to the relevant function argument.The PHP SDK needs the typing information at runtime to correctly report to the API. :::
Here is an example call for this Dagger Function:
dagger call hello --names=John,Jane
The result will look like this:
Hello John, Jane
You can also pass a directory argument from the command-line. To do so, add the corresponding flag, followed by a local filesystem path or a remote Git reference. In both cases, the CLI will convert it to an object referencing the contents of that filesystem path or Git repository location, and pass the resulting Directory object as argument to the Dagger Function.
Dagger Functions do not have access to the filesystem of the host you invoke the Dagger Function from (i.e. the host you execute a CLI command like dagger call from). Instead, host directories need to be explicitly passed as arguments to Dagger Functions.
Here's an example of a Dagger Function that accepts a Directory as argument. The Dagger Function returns a tree representation of the files and directories at that path.
Here is an example of passing a local directory to this Dagger Function as argument:
mkdir -p mydir/mysubdir
touch mydir/a mydir/b mydir/c mydir/mysubdir/y mydir/mysubdir/z
dagger call tree --src=mydir --depth=2
The result will look like this:
.
├── a
├── b
├── c
└── mysubdir
├── y
└── z
2 directories, 5 files
Here is an example of passing a remote repository (Dagger's open-source repository) over HTTPS as a Directory argument:
dagger core container \
from --address=alpine:latest \
with-directory --path=/src --directory=https://github.com/dagger/dagger \
with-exec --args="ls","/src" \
stdout
The same repository can also be accessed using SSH. Note that this requires SSH authentication to be properly configured on your Dagger host. Here is the same example, this time using SSH:
dagger core container \
from --address=alpine:latest \
with-directory --path=/src --directory=ssh://[email protected]/dagger/dagger \
with-exec --args="ls","/src" \
stdout
For more information about remote repository access, refer to the documentation on reference schemes and authentication methods.
:::note
Dagger offers two important features for working with Directory arguments:
File arguments work in the same way as directory arguments. To pass a file to a Dagger Function as an argument, add the corresponding flag, followed by a local filesystem path or a remote Git reference. In both cases, the CLI will convert it to an object referencing that filesystem path or Git repository location, and pass the resulting File object as argument to the Dagger Function.
Here's an example of a Dagger Function that accepts a File as argument, reads it, and returns its contents:
Here is an example of passing a local file to this Dagger Function as argument:
dagger call read-file --source=/my/file/path/README.md
And here is an example of passing a file from a remote Git repository as argument:
dagger call read-file --source=https://github.com/dagger/dagger.git#main:README.md
For more information about remote repository access, refer to the documentation on reference schemes and authentication methods.
:::note
Dagger offers two important features for working with File arguments:
Just like directories, you can pass a container to a Dagger Function from the command-line. To do so, add the corresponding flag, followed by the address of an OCI image. The CLI will dynamically pull the image, and pass the resulting Container object as argument to the Dagger Function.
Here is an example of a Dagger Function that accepts a container image reference as an argument. The Dagger Function returns operating system information for the container.
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-container/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-container/python/main.py ``` </TabItem> <TabItem value="TypeScript"> ```typescript file=./snippets/functions/arguments-container/typescript/index.ts ``` </TabItem> <TabItem value="PHP"> ```php file=./snippets/functions/arguments-container/php/src/MyModule.php ``` </TabItem> <TabItem value="Java"> ```java file=./snippets/functions/arguments-container/java/src/main/java/io/dagger/modules/mymodule/MyModule.java ``` </TabItem> </Tabs>Here is an example of passing a container image reference to this Dagger Function as an argument.
dagger call os-info --ctr=ubuntu:latest
The result will look like this:
Linux buildkitsandbox 6.1.0-22-cloud-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.94-1 (2024-06-21) x86_64 x86_64 x86_64 GNU/Linux
Here is another example of passing a container image reference to a Dagger Function as an argument. The Dagger Function scans the container using Trivy and reports any vulnerabilities found.
dagger -m github.com/jpadams/daggerverse/[email protected] call scan-container --ctr=index.docker.io/alpine:latest
Dagger allows you to utilize confidential information, such as passwords, API keys, SSH keys and so on, in your Dagger modules and Dagger Functions, without exposing those secrets in plaintext logs, writing them into the filesystem of containers you're building, or inserting them into the cache.
Secrets can be passed to Dagger Functions as arguments using the Secret core type. Here is an example of a Dagger Function which accepts a GitHub personal access token as a secret, and uses the token to authorize a request to the GitHub API:
The result will be a JSON-formatted list of issues from Dagger's repository.
When invoking the Dagger Function using the Dagger CLI, secrets can be sourced from multiple providers. Dagger can read secrets from the host environment, the host filesystem, and the result of host command execution, as well as from external secret managers 1Password and Vault.
Here is an example call for this Dagger Function, with the secret sourced from a host environment variable named GITHUB_API_TOKEN via the env provider:
dagger call github-api --token=env://GITHUB_API_TOKEN
Secrets can also be passed from a host file using the file provider:
dagger call github-api --token=file://./github.txt
...or as the result of executing a command on the host using the cmd provider:
dagger call github-api --token=cmd://"gh auth token"
Secrets can also be sourced from external secret managers. Currently, Dagger supports 1Password and Vault.
1Password requires creating a service account and then setting the OP_SERVICE_ACCOUNT_TOKEN environment variable. Alternatively, if no OP_SERVICE_ACCOUNT_TOKEN is provided, the integration will attempt to execute the (official) op CLI if installed in the system.
1Password secret references, in the format op://VAULT-NAME/ITEM-NAME/[SECTION-NAME/]FIELD-NAME are supported. Here is an example:
OP_SERVICE_ACCOUNT_TOKEN="mytoken" dagger call github-api --token=op://infra/github/credential
Vault can be authenticated with either token or AppRole methods. The Vault host can be specified by setting the environment variable VAULT_ADDR. For token authentication, set the environment variable VAULT_TOKEN. For AppRole authentication, set the environment variables VAULT_APPROLE_ROLE_ID and VAULT_APPROLE_SECRET_ID. Additional client configuration can be specified by the default environment variables accepted by Vault.
Vault KvV2 secrets are accessed with the scheme vault://PATH/TO/SECRET.ITEM. If your KvV2 is not mounted at /secret, specify the mount location with the environment variable VAULT_PATH_PREFIX. Here is an example:
VAULT_ADDR='https://example.com:8200' VAULT_TOKEN=abcd_1234 dagger call github-api --token=vault://infra/github.credential
```shell
dagger call github-api --token=vault://credentials.github
Host network services or sockets can be passed to Dagger Functions as arguments. To do so, add the corresponding flag, followed by a service or socket reference.
To pass host TCP or UDP network services as arguments when invoking a Dagger Function, specify them in the form tcp://HOST:PORT or udp://HOST:PORT.
Assume that you have a PostgresQL database running locally on port 5432, as with:
docker run -d -e POSTGRES_PASSWORD=postgres -p 5432:5432 postgres
Here is an example of passing this host service as argument to a PostgreSQL client Dagger Function, which drops you to a prompt from where you can execute SQL queries:
dagger -m github.com/kpenfound/dagger-modules/[email protected] call client --db=postgres --user=postgres --password=postgres --server=tcp://localhost:5432
Similar to host TCP/UDP services, Dagger Functions can also be granted access to host Unix sockets when the client is running on Linux or MacOS.
To pass host Unix sockets as arguments when invoking a Dagger Function, specify them by their path on the host.
For example, assuming you have Docker on your host with the Docker daemon listening on a Unix socket at /var/run/docker.sock, you can pass this socket to a Docker client Dagger Function as follows:
dagger -m github.com/sipsma/daggerverse/[email protected] call --sock=/var/run/docker.sock version
Function arguments can be marked as optional. In this case, the Dagger CLI will not display an error if the argument is omitted in the function call.
Here's an example of a Dagger Function with an optional argument:
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-optional/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-optional/python/main.py ``` </TabItem> <TabItem value="TypeScript"> ```typescript file=./snippets/functions/arguments-optional/typescript/index.ts ``` </TabItem> <TabItem value="PHP"> :::note The definition of optional varies between Dagger and PHP.An optional argument to PHP is one that has a default value.
An optional argument to Dagger can be omitted entirely. It is truly optional.
To specify a function argument as optional, simply make it nullable. When using the Dagger CLI, if the argument is omitted; the PHP SDK will treat this as receiving the value null.
:::
When an argument is not set as optional, Dagger will ensure the value is not null by adding a call to Objects.requireNonNull against the argument.
:::
Here is an example call for this Dagger Function, with the optional argument:
dagger call hello --name=John
The result will look like this:
Hello, John
Here is an example call for this Dagger Function, without the optional argument:
dagger call hello
The result will look like this:
Hello, world
Function arguments can define a default value if no value is supplied for them.
Here's an example of a Dagger Function with a default value for a string argument:
<Tabs groupId="language"> <TabItem value="Go"> ```go file=./snippets/functions/arguments-default-string/go/main.go ``` </TabItem> <TabItem value="Python"> ```python file=./snippets/functions/arguments-default-string/python/main.py ``` </TabItem> <TabItem value="TypeScript"> ```typescript file=./snippets/functions/arguments-default-string/typescript/index.ts ``` </TabItem> <TabItem value="PHP"> ```php file=./snippets/functions/arguments-default-string/php/src/MyModule.php ``` </TabItem> <TabItem value="Java"> :::note The default value provided must be a valid JSON string representation of the type.For instance if the argument is of type Integer and the default value is 123, then the annotation must be @Default("123").
If the argument is of type String and the default value is world, then the annotation should be @Default("\"world\"").
In order to simplify this very specific case, if the argument is of type String and the value doesn't start with an escaped quote,
then the SDK will automatically add the escaped quotes for you. That way you can simply write @Default("world").
:::
Here is an example call for this Dagger Function, without the required argument:
dagger call hello
The result will look like this:
Hello, world
Passing null to an optional argument signals that no default value should be used.
:::note
Dagger supports default paths for Directory or File arguments. Dagger will automatically use this default path when no value is specified for the corresponding argument.
:::
Dagger supports the use of HTTP and SSH protocols for accessing files and directories in remote repositories, compatible with all major Git hosting platforms such as GitHub, GitLab, BitBucket, Azure DevOps, Codeberg, and Sourcehut. Dagger supports authentication via both HTTPS (using Git credential managers) and SSH (using a unified authentication approach).
Dagger supports the following reference schemes for file and directory arguments:
| Protocol | Scheme | Authentication | Example |
|---|---|---|---|
| HTTP(S) | Git HTTP | Git credential manager | https://github.com/username/repo.git[#version[:subpath]] |
| SSH | Explicit | SSH keys | ssh://[email protected]/username/repo.git[#version[:subpath]] |
| SSH | SCP-like | SSH keys | [email protected]:username/repo.git[#version[:subpath]] |
:::note The reference scheme for directory arguments is currently under discussion here and here and may change in future. :::
Dagger provides additional flexibility in referencing file and directory arguments through the following options:
#version to target a particular version of the repository. This can be a tag, branch name, or full commit hash. If omitted, the default branch is used.:subpath after the version specification to access a specific subdirectory within the repository. Note that specifying a version is mandatory when including a subpath.:::important
When referencing a specific subdirectory (subpath) within a repository, you must always include a version specification. The format is always #version:subpath.
:::