---
title: Attribute Expressions
description: Match units and stacks by their configuration attributes
slug: features/filter/attributes
sidebar:
  order: 4
---

import { Aside } from '@astrojs/starlight/components';
import FileTree from '@components/vendored/starlight/FileTree.astro';

Match units and stacks by their configuration attributes.

```bash
# Filter by component type
terragrunt find --filter 'type=unit'
terragrunt find --filter 'type=stack'

# Filter by external dependency status
terragrunt find --filter '{./**}... | external=false'
terragrunt find --filter '{./**}... | external=true'

# Explicitly filter by name (useful for explicitly indicating that this is a name expression)
terragrunt find --filter 'name=stack*'
```

<FileTree>
- .
  - **unit1** \<-- Matched by the first filter
    - terragrunt.hcl
  - **stack1** \<-- Matched by the second and fifth filter
    - terragrunt.stack.hcl
- ..
  - dependencies \<-- Note that this directory is sibling to the current working directory
    - **dependency-of-app1** \<-- Matched by the fourth filter, but not the third filter
        - terragrunt.hcl
</FileTree>

The following are the attributes supported for attribute-based expressions:

| Attribute | Description |
|-----------|-------------|
| name | Match units and stacks by their directory basename. |
| type | Match units and stacks by their type. |
| external | Match units and stacks if they are external to the current working directory. |
| reading | Match units and stacks by the files they read. |
| source | Match units and stacks by their Terraform source URL or path specified in the `terraform` block of `terragrunt.hcl` files. |

## Reading-Based Expressions

Match units and stacks by the files they read.

Consider the following file tree:

<FileTree>

- reading-shared-hcl
  - terragrunt.hcl
- also-reading-shared-hcl
  - terragrunt.hcl
- not-reading-shared-hcl
  - terragrunt.hcl
- shared.hcl

</FileTree>

Suppose that `reading-shared-hcl` and `also-reading-shared-hcl` both read `shared.hcl` in their configurations, like so:

```hcl
# terragrunt.hcl

locals {
 shared = read_terragrunt_config(find_in_parent_folders("shared.hcl"))
}
```

If you run the command `terragrunt run --all --filter 'reading=shared.hcl' -- plan` from the root folder, both
`reading-shared-hcl` and `also-reading-shared-hcl` will be run; not `not-reading-shared-hcl`.

This is because the `read_terragrunt_config` HCL function has a special hook that allows Terragrunt to track that it has
read the file `shared.hcl`. This hook is used by all native HCL functions that Terragrunt supports which read files.

Note, however, that there are certain scenarios where Terragrunt may not be able to track that a file has been read this way.

For example, you may be using a bash script to read a file via [`run_cmd`](/reference/hcl/functions/#run_cmd), or reading the file via OpenTofu/Terraform code. To support these
use-cases, the [`mark_as_read`](/reference/hcl/functions/#mark_as_read) function can be used to explicitly mark a file as read in the unit.

That would look something like this:

```hcl
# terragrunt.hcl

locals {
  filename = mark_as_read("file-read-by-tofu.txt")
}

inputs = {
  filename = local.filename
}
```
<Aside type="caution">
Due to how Terragrunt parses configurations during `run --all`, functions will only properly mark files as read if they are used outside the `inputs` attribute.

Reading a file directly in the `inputs` attribute will not mark the file as read, as the `inputs` attribute is not parsed until after the queue has already been populated to support rendering of dependency outputs, which are only available after dependencies have been run.
</Aside>

To mark many files at once, use [`mark_glob_as_read`](/reference/hcl/functions/#mark_glob_as_read), which accepts a glob (with `**` support) and marks every matching file.

If a unit's `terraform` block points at a local module source, enable the [`mark-many-as-read`](/reference/experiments/active#mark-many-as-read) experiment to have Terragrunt automatically mark that module's `*.tf`, `*.tf.json`, `*.hcl`, `*.tofu`, and `*.tofu.json` files as read. Reading-based filters will then cascade local module changes to every unit that consumes the module. The same experiment also enables the [`mark_glob_as_read`](/reference/hcl/functions/#mark_glob_as_read) HCL function.

## Source-Based Expressions

Match units and stacks by their Terraform source URL or path specified in the `terraform` block of `terragrunt.hcl` files.

```bash
# Filter by exact source match
terragrunt find --filter 'source=github.com/acme/foo'
terragrunt find --filter 'source=gitlab.com/example/baz'
terragrunt find --filter 'source=./module'

# Filter by source using glob patterns
terragrunt find --filter 'source=*github.com**acme/*'
terragrunt find --filter 'source=git::git@github.com:acme/**'
terragrunt find --filter 'source=**github.com**'
terragrunt find --filter 'source=gitlab.com/**'
```

<FileTree>
- .
  - **github-acme-foo** \<-- Matched by source=github.com/acme/foo and source=*github.com**acme/*
    - terragrunt.hcl (source: github.com/acme/foo)
  - **github-acme-bar** \<-- Matched by source=*github.com**acme/* and source=git::git@github.com:acme/**
    - terragrunt.hcl (source: git::git@github.com:acme/bar)
  - **gitlab-example-baz** \<-- Matched by source=gitlab.com/example/baz and source=gitlab.com/**
    - terragrunt.hcl (source: gitlab.com/example/baz)
  - **local-module** \<-- Matched by source=./module
    - terragrunt.hcl (source: ./module)
    - module
      - main.tf
  - other-unit
    - terragrunt.hcl (source: s3://bucket/module)
</FileTree>

<Aside type="note">
The `source=` filter matches against the Terraform source URL or path specified in the `terraform` block of `terragrunt.hcl` files in units. It supports glob patterns, allowing you to match multiple sources with patterns like `*github.com**` or `gitlab.com/**`. This is useful for filtering units that use specific module sources, such as all units using a particular GitHub organization's modules or all local modules.

This attribute may be supported on stacks in the future.
</Aside>
