🔤 Placeholder Substitution Action

This GitHub Action replaces placeholder variables in text-based config files using environment variables.

It supports patterns like:

• $(VAR)
• ${VAR}
• #{VAR}
• <<VAR>>

---

✅ Features

• 🔁 Replaces variable placeholders with values from environment variables
• ✨ Customizable prefix and suffix (${VAR}, $(VAR), etc.)
• 🔠 Case-insensitive matching for variable names
• ✨ Supports glob patterns like **/*.asa
• 🚫 Automatically deduplicates matched files
• 🛡️ Fails cleanly if no files matched
• 🧾 Works with .config, .asa, .env, .json, etc.
• ⚙️ Fully cross-platform (Windows, Linux, macOS)

---

🔧 Inputs

Input	Description	Required	Default
files	Newline-separated list of XML file paths	✅
prefix	Prefix for placeholder (e.g., #{)	❌	#{
suffix	Suffix for placeholder (e.g., })	❌	}

---

🖥️ Compatibility

• ✅ ubuntu-latest
• ✅ windows-latest
• ✅ macos-latest
• 🔧 Requires PowerShell Core

---

🚀 Usage

Because GitHub Actions composite actions cannot directly access the vars, inputs, or secrets contexts, you must manually pass any required values through the env block (see example below). Alternatively you can dump all variables as environment variables using the following script in a step before calling this action:

⚠️ Warning: Dumping all variables may expose sensitive information. Use with caution.

- name: Export all GitHub vars
  run: |
    $json = '${{ toJson(vars) }}'
	$vars = ConvertFrom-Json $json
	foreach ($property in $vars.PSObject.Properties) {
	  $key = $property.Name
	  $value = $property.Value
	  Write-Host "Setting $key to $value"
	  $output = "${key}<<EOF`n${value}`nEOF" # Needed if any value contains a new-line (\r\n)
	  Add-Content -Path $Env:GITHUB_ENV -Value $output
    }
    Write-Host "Variables exported successfully."

🧪 Example workflow step setting environment variables manually

- name: Substitute placeholders in files
  uses: CasperWSchmidt/substitute-vars-action@v1
  with:
    files: |
      deploy/global.asa
      deploy/**/*.config
    prefix: '${'
    suffix: '}'
  env: # required to pass variables into the action
    ENVIRONMENT: ${{ inputs.environment }}
    CONNECTION_STRING: ${{ secrets.MY_DATABASE_CONNECTION  }}
	ROOT_DIRECTORY: ${{ vars.MY_ROOT_DIRECTORY }}

🧪 Example workflow step using dynamic variable export

- name: Export all GitHub vars
  run: |
    $json = '${{ toJson(vars) }}'
	$vars = ConvertFrom-Json $json
	foreach ($property in $vars.PSObject.Properties) {
	  $key = $property.Name
	  $value = $property.Value
	  Write-Host "Setting $key to $value"
	  $output = "${key}<<EOF`n${value}`nEOF" # Needed if any value contains a new-line (\r\n)
	  Add-Content -Path $Env:GITHUB_ENV -Value $output
    }
    Write-Host "Variables exported successfully."
	
- name: Substitute placeholders in files
  uses: CasperWSchmidt/substitute-vars-action@v1
  with:
    files: |
      deploy/global.asa
      deploy/**/*.config
    prefix: '${'
    suffix: '}'

🗂️ Example web.config (before)

<configuration>
  <appSettings>
    <add key="Environment" value="#{ENVIRONMENT}" />
    <add key="RootDirectory" value="#{ROOT_DIRECTORY}" />
  </appSettings>
  <connectionStrings>
    <add name="DefaultConnection" connectionString="#{CONNECTION_STRING}" />
  </connectionStrings>
</configuration>

✅ Result (after)

<configuration>
  <appSettings>
    <add key="Environment" value="Production" />
    <add key="RootDirectory" value="C:\Some\Path" />
  </appSettings>
  <connectionStrings>
    <add name="DefaultConnection" connectionString="Server=sql;Database=prod;User Id=admin;" />
  </connectionStrings>
</configuration>