# replace-file-content

Learn how to replace content in files using patterns.

This action replaces content in files using regular expression patterns.

All occurrences of each pattern are replaced, and replacements are applied sequentially within each file, so later replacements operate on the result of earlier ones.

## Example

The following template updates the project name in a configuration file:

**template.json5**

```json5
{
  "$schema": "https://schema.croct.com/json/v1/template.json",
  "title": "Config updater",
  "description": "Updates the project name in the config file.",
  "options": {
    "name": {
      "type": "string",
      "description": "The project name.",
      "default": "my-app"
    }
  },
  "actions": [
    {
      "name": "replace-file-content",
      "files": [
        {
          "path": "config.json",
          "replacements": [
            {
              "pattern": "\"name\": \".*\"",
              "value": "\"name\": \"${options.name}\""
            }
          ]
        }
      ]
    }
  ]
}
```

To apply this template, run:

```sh
croct use template.json5 --name my-app
```

### Capture groups

Use capture groups in the pattern to reference matched segments in the replacement value with `$1`, `$2`, and so on:

**template.json5**

```json5
{
  "$schema": "https://schema.croct.com/json/v1/template.json",
  "title": "Import updater",
  "description": "Rewrites import paths.",
  "actions": [
    {
      "name": "replace-file-content",
      "files": [
        {
          "path": "src/index.ts",
          "replacements": [
            {
              "pattern": "from ['\"]@/lib/(.*)['\"]",
              "value": "from '@/utils/$1'"
            }
          ]
        }
      ]
    }
  ]
}
```

All imports from `@/lib/` are rewritten to `@/utils/`, preserving the original module name through the `$1` reference.

## Properties

These are the supported properties:

- `name`: `string`

  The action identifier. Always `replace-file-content` for this action.

- `files`: `Array<object>`

  The list of files to process.

  Each entry specifies a file path and the replacements to apply. The action fails if no files match.

  - `path`: `string`

    The path to the file.

  - `replacements`: `Array<object>`

    The list of replacements to apply in order.

    - `pattern`: `string`

      The regular expression to match.

      Capture groups like `$1` and `$2` can be referenced in the replacement value.

    - `value`: `string | number`

      The replacement value.

    - `caseSensitive`: `boolean` (optional) (default: false)

      Whether to ignore case when matching.

      When enabled, the pattern matches regardless of letter casing.

## Explore

- [Read file](/reference/cli/templates/actions/read-file): Learn how to read the file before replacing.
- [Write file](/reference/cli/templates/actions/write-file): Learn how to write a new file from scratch.
- [Format code](/reference/cli/templates/actions/format-code): Learn how to format the modified file.
- [Resolve import](/reference/cli/templates/actions/resolve-import): Learn how to resolve an import path to inject.