docs/versions/9.3.0/rules/lib/builtins/Action.mdx

---
title: 'Action'
---
An action created during rule analysis.

This object is visible for the purpose of testing, and may be obtained from an `Actions` provider. It is normally not necessary to access `Action` objects or their fields within a rule's implementation function. You may instead want to see the [Rules page](https://bazel.build/versions/9.3.0/extending/rules#actions) for a general discussion of how to use actions when defining custom rules, or the [API reference](../builtins/actions) for creating actions.

Some fields of this object are only applicable for certain kinds of actions. Fields that are inapplicable are set to `None`.

## Members

* [args](#args)
* [argv](#argv)
* [content](#content)
* [env](#env)
* [inputs](#inputs)
* [mnemonic](#mnemonic)
* [outputs](#outputs)
* [substitutions](#substitutions)

## args {#args}

```
sequence Action.args
```

A list of frozen [Args](../builtins/Args) objects containing information about the action arguments. These objects contain accurate argument information, including arguments involving expanded action output directories. However, [Args](../builtins/Args) objects are not readable in the analysis phase. For a less accurate account of arguments which is available in the analysis phase, see [argv](#argv).

Note that some types of actions do not yet support exposure of this field. For such action types, this is `None`.
May return `None`.
## argv {#argv}

```
sequence Action.argv
```

For actions created by [ctx.actions.run()](../builtins/actions#run) or [ctx.actions.run_shell()](../builtins/actions#run_shell) an immutable list of the arguments for the command line to be executed. Note that for shell actions the first two arguments will be the shell path and `"-c"`.
May return `None`.
## content {#content}

```
string Action.content
```

For actions created by [ctx.actions.write()](../builtins/actions#write) or [ctx.actions.expand_template()](../builtins/actions#expand_template), the contents of the file to be written, if those contents can be computed during the analysis phase. The value is `None` if the contents cannot be determined until the execution phase, such as when a directory in an [Args](../builtins/Args) object needs to be expanded.
May return `None`.
## env {#env}

```
dict Action.env
```

The 'fixed' environment variables for this action. This includes only environment settings which are explicitly set by the action definition, and thus omits settings which are only pre-set in the execution environment.
## inputs {#inputs}

```
depset Action.inputs
```

A set of the input files of this action.
## mnemonic {#mnemonic}

```
string Action.mnemonic
```

The mnemonic for this action.
## outputs {#outputs}

```
depset Action.outputs
```

A set of the output files of this action.
## substitutions {#substitutions}

```
dict Action.substitutions
```

For actions created by [ctx.actions.expand_template()](../builtins/actions#expand_template), an immutable dict holding the substitution mapping.
May return `None`.