diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index df9fd3a..9da756c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -16,10 +16,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Test with Pester
-        run: |
-          Install-Module -Name Pester -Force -SkipPublisherCheck -MinimumVersion '5.0'
-          Import-Module Pester -MinimumVersion '5.0'
-          Invoke-Pester -CI
+        run: ./test.ps1
       - name: Invoke action
         env:
           TEMP: ${{ runner.temp }}
@@ -234,18 +231,20 @@ jobs:
 
       # Invoke-ActionNoCommandsBlock
       - name: Invoke-ActionNoCommandsBlock test (act)
-        uses: ./
-        with:
-          script: |
+        id: Invoke-ActionNoCommandsBlock
+        shell: pwsh
+        run: |
+            Import-Module ./lib/GitHubActionsCore -Force
             Invoke-ActionNoCommandsBlock -GenerateToken {
-              Set-ActionVariable nocmdvar nocmd
+              Set-ActionOutput testout testval
             }
       - name: Invoke-ActionNoCommandsBlock test (assert)
         uses: ./
         with:
           script: |
-            if ($env:nocmdvar -ne $null) {
-              throw "Invoke-ActionNoCommandsBlock failed.`n$env:nocmdvar"
+            $result = '${{ steps.Invoke-ActionNoCommandsBlock.outputs.testout }}'
+            if ($result) {
+              throw "Invoke-ActionNoCommandsBlock failed.`n$result"
             }
 
       # Write-Action -Debug, -Info, -Warning, -Error and Grouping are not testable in any sensible manner
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1ad70c3..653565d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,17 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+- `Send-ActionFileCommand` cmdlet that handles sending commands to [Environment Files] instead of console output ([#8]).
+
+### Changed
+- `Add-ActionPath` and `Set-ActionVariable` are updated for [Environment Files] Actions Runner change ([#8]).
+
+[Environment Files]: https://docs.github.com/en/actions/reference/workflow-commands-for-github-actions#environment-files
+[#8]: https://github.com/Amadevus/pwsh-script/pull/8
+
 ## [2.0.0] - 2020-09-10
 
 ### Changed
diff --git a/docs/GitHubActionsCore/README.md b/docs/GitHubActionsCore/README.md
index 1b6e914..20147f3 100644
--- a/docs/GitHubActionsCore/README.md
+++ b/docs/GitHubActionsCore/README.md
@@ -9,6 +9,7 @@
 | [Invoke-ActionGroup](Invoke-ActionGroup.md) | Executes the argument script block within an output group. Equivalent of `core.group(name, func)`. |
 | [Invoke-ActionNoCommandsBlock](Invoke-ActionNoCommandsBlock.md) | Invokes a scriptblock that won't result in any output interpreted as a workflow command. Useful for printing arbitrary text that may contain command-like text. No quivalent in `@actions/core` package. |
 | [Send-ActionCommand](Send-ActionCommand.md) | Sends a command to the hosting Workflow/Action context. Equivalent to `core.issue(cmd, msg)`/`core.issueCommand(cmd, props, msg)`. |
+| [Send-ActionFileCommand](Send-ActionFileCommand.md) | Sends a command to an Action Environment File. Equivalent to `core.issueFileCommand(cmd, msg)`. |
 | [Set-ActionCommandEcho](Set-ActionCommandEcho.md) | Enables or disables the echoing of commands into stdout for the rest of the step. Echoing is disabled by default if ACTIONS_STEP_DEBUG is not set. Equivalent of `core.setCommandEcho(enabled)`. |
 | [Set-ActionFailed](Set-ActionFailed.md) | Sets an action status to failed. When the action exits it will be with an exit code of 1. Equivalent of `core.setFailed(message)`. |
 | [Set-ActionOutput](Set-ActionOutput.md) | Sets the value of an output. Equivalent of `core.setOutput(name, value)`. |
diff --git a/docs/GitHubActionsCore/Send-ActionFileCommand.md b/docs/GitHubActionsCore/Send-ActionFileCommand.md
new file mode 100644
index 0000000..7c04e79
--- /dev/null
+++ b/docs/GitHubActionsCore/Send-ActionFileCommand.md
@@ -0,0 +1,72 @@
+# Send-ActionFileCommand
+```
+
+NAME
+    Send-ActionFileCommand
+    
+SYNOPSIS
+    Sends a command to an Action Environment File.
+    Equivalent to `core.issueFileCommand(cmd, msg)`.
+    
+    
+SYNTAX
+    Send-ActionFileCommand [-Command] <String> [-Message] <PSObject> [<CommonParameters>]
+    
+    
+DESCRIPTION
+    Appends given message to an Action Environment File.
+    
+
+PARAMETERS
+    -Command <String>
+        Command (environment file variable suffix) to send message for.
+        
+        Required?                    true
+        Position?                    1
+        Default value                
+        Accept pipeline input?       false
+        Accept wildcard characters?  false
+        
+    -Message <PSObject>
+        Message to append.
+        
+        Required?                    true
+        Position?                    2
+        Default value                
+        Accept pipeline input?       true (ByValue)
+        Accept wildcard characters?  false
+        
+    <CommonParameters>
+        This cmdlet supports the common parameters: Verbose, Debug,
+        ErrorAction, ErrorVariable, WarningAction, WarningVariable,
+        OutBuffer, PipelineVariable, and OutVariable. For more information, see
+        about_CommonParameters (https://go.microsoft.com/fwlink/?LinkID=113216). 
+    
+INPUTS
+    
+OUTPUTS
+    
+    -------------------------- EXAMPLE 1 --------------------------
+    
+    PS>Send-ActionFileCommand ENV 'myvar=value'
+    
+    
+    
+    
+    
+    
+    -------------------------- EXAMPLE 2 --------------------------
+    
+    PS>'myvar=value', 'myvar2=novalue' | Send-ActionFileCommand ENV
+    
+    
+    
+    
+    
+    
+    
+RELATED LINKS
+    https://docs.github.com/en/actions/reference/workflow-commands-for-github-actions#environment-files
+
+```
+
diff --git a/lib/GitHubActionsCore/GitHubActionsCore.Tests.ps1 b/lib/GitHubActionsCore/GitHubActionsCore.Tests.ps1
index 35380c6..30541d6 100644
--- a/lib/GitHubActionsCore/GitHubActionsCore.Tests.ps1
+++ b/lib/GitHubActionsCore/GitHubActionsCore.Tests.ps1
@@ -1,36 +1,34 @@
-Set-StrictMode -Version Latest
+#Requires -Module @{ ModuleName = 'Pester'; ModuleVersion = '5.1' }
 
 BeforeAll {
-    Get-Module GitHubActionsCore | Remove-Module
-    Import-Module $PSScriptRoot
+    Import-Module $PSScriptRoot -Force
 }
 
 Describe 'Get-ActionInput' {
+    BeforeEach {
+        $env:INPUT_TEST_INPUT = $null
+    }
     Context "When requested input doesn't exist" {
         It "Should return empty string" {
-            $result = Get-ActionInput ([Guid]::NewGuid())
+            $result = Get-ActionInput TEST_INPUT
             $result | Should -Be ''
         }
         It "Given Required switch, it throws" {
             {
-                Get-ActionInput ([Guid]::NewGuid()) -Required
+                Get-ActionInput TEST_INPUT -Required
             } | Should -Throw
         }
     }
     Context "When requested input exists" {
         It "Should return it's value" {
-            Mock Get-ChildItem { @{Value = 'test value' } } {
-                $Path -eq 'Env:INPUT_TEST_INPUT'
-            } -ModuleName GitHubActionsCore
+            $env:INPUT_TEST_INPUT = 'test value'
 
             $result = Get-ActionInput TEST_INPUT
 
             $result | Should -Be 'test value'
         }
         It "Should trim the returned value" {
-            Mock Get-ChildItem { @{Value = "`n  test value `n  `n" } } {
-                $Path -eq 'Env:INPUT_TEST_INPUT'
-            } -ModuleName GitHubActionsCore
+            $env:INPUT_TEST_INPUT = "`n  test value `n  `n"
 
             $result = Get-ActionInput TEST_INPUT
 
@@ -39,15 +37,16 @@ Describe 'Get-ActionInput' {
     }
     Context "When input name contains spaces" {
         It "Should replace them with underscores" {
-            Mock Get-ChildItem { @{Value = 'value' } } {
-                $Path -eq 'Env:INPUT_TEST_INPUT'
-            } -ModuleName GitHubActionsCore
+            $env:INPUT_TEST_INPUT = 'test value'
 
             $result = Get-ActionInput 'test input'
 
-            $result | Should -Be 'value'
+            $result | Should -Be 'test value'
         }
     }
+    AfterEach {
+        $env:INPUT_TEST_INPUT = $null
+    }
 }
 Describe 'Set-ActionOutput' {
     BeforeAll {
@@ -75,56 +74,131 @@ Describe 'Add-ActionSecret' {
 }
 Describe 'Set-ActionVariable' {
     BeforeAll {
-        Mock Write-Host { } -ModuleName GitHubActionsCore
+        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterAll')]
+        $oldGithubEnv = $env:GITHUB_ENV
+        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterAll')]
+        $oldTestVar = $env:TESTVAR
     }
     BeforeEach {
-        Remove-Item "Env:my-var" -ErrorAction SilentlyContinue
+        $env:GITHUB_ENV = $null
+        $env:TESTVAR = $null
+    }
+    AfterAll {
+        $env:GITHUB_ENV = $oldGithubEnv
+        $env:TESTVAR = $oldTestVar
     }
-    It "Given value '<value>', sends command with '<expectedcmd>' and sets env var to '<expectedenv>'" -TestCases @(
+    Context "Given value '<value>'" -Foreach @(
         @{ Value = ''; ExpectedCmd = ''; ExpectedEnv = $null }
         @{ Value = 'test value'; ExpectedCmd = 'test value'; ExpectedEnv = 'test value' }
         @{ Value = 'A % B'; ExpectedCmd = 'A %25 B'; ExpectedEnv = 'A % B' }
         @{ Value = [ordered]@{ a = '1x'; b = '2y' }; ExpectedCmd = '{"a":"1x","b":"2y"}'; ExpectedEnv = '{"a":"1x","b":"2y"}' }
     ) {
-        Set-ActionVariable 'my-var' $Value
-
-        ${env:my-var} | Should -Be $ExpectedEnv
-        Should -Invoke Write-Host -ParameterFilter {
-            $Object -eq "::set-env name=my-var::$ExpectedCmd"
-        } -ModuleName GitHubActionsCore
-    }
-    AfterEach {
-        Remove-Item "Env:my-var" -ErrorAction SilentlyContinue
+        Context "When GITHUB_ENV not set" {
+            BeforeAll {
+                Mock Write-Host { } -ModuleName GitHubActionsCore
+            }
+            It "Sends command with '<expectedcmd>' and sets env var to '<expectedenv>'" {
+                Set-ActionVariable TESTVAR $Value
+        
+                $env:TESTVAR | Should -Be $ExpectedEnv
+                Should -Invoke Write-Host -ParameterFilter {
+                    $Object -eq "::set-env name=TESTVAR::$ExpectedCmd"
+                } -ModuleName GitHubActionsCore
+            }
+            It "Sends command with '<expectedcmd>' and doesn't set env var due to -SkipLocal" {
+                Set-ActionVariable TESTVAR $Value -SkipLocal
+        
+                $env:TESTVAR | Should -BeNullOrEmpty
+                Should -Invoke Write-Host -ParameterFilter {
+                    $Object -eq "::set-env name=TESTVAR::$ExpectedCmd"
+                } -ModuleName GitHubActionsCore
+            }
+        }
+        Context "When GITHUB_ENV is set" {
+            BeforeEach {
+                $testPath = 'TestDrive:/env-cmd.env'
+                Set-Content $testPath '' -NoNewline
+                $env:GITHUB_ENV = $testPath
+            }
+            It "Appends command file with formatted command and sets env var to '<expectedenv>'" {
+                Set-ActionVariable TESTVAR $Value
+        
+                $env:TESTVAR | Should -Be $ExpectedEnv
+                $eol = [System.Environment]::NewLine
+                Get-Content $testPath -Raw
+                | Should -BeExactly "TESTVAR<<_GitHubActionsFileCommandDelimeter_${eol}$ExpectedEnv${eol}_GitHubActionsFileCommandDelimeter_${eol}"
+            }
+            It "Appends command file with formatted command and doesn't set env var due to -SkipLocal" {
+                Set-ActionVariable TESTVAR $Value -SkipLocal
+        
+                $env:TESTVAR | Should -BeNullOrEmpty
+                $eol = [System.Environment]::NewLine
+                Get-Content $testPath -Raw
+                | Should -BeExactly "TESTVAR<<_GitHubActionsFileCommandDelimeter_${eol}$ExpectedEnv${eol}_GitHubActionsFileCommandDelimeter_${eol}"
+            }
+        }
     }
 }
 Describe 'Add-ActionPath' {
     BeforeAll {
-        Mock Write-Host { } -ModuleName GitHubActionsCore
+        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterAll')]
+        $oldPath = $env:PATH
+        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterAll')]
+        $oldGithubPath = $env:GITHUB_PATH
     }
     BeforeEach {
-        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterEach')]
-        $prevPath = [System.Environment]::GetEnvironmentVariable('PATH')
+        $env:PATH = $oldPath
+        $env:GITHUB_PATH = $null
     }
-    It "Sends appropriate workflow command to host and prepends PATH" {
-        Add-ActionPath 'test path'
-
-        $env:PATH | Should -BeLike "test path$([System.IO.Path]::PathSeparator)*" -Because 'PATH should be also prepended in current scope'
-        Should -Invoke Write-Host -ParameterFilter {
-            $Object -eq '::add-path::test path'
-        } -ModuleName GitHubActionsCore
+    AfterAll {
+        $env:PATH = $oldPath
+        $env:GITHUB_PATH = $oldGithubPath
     }
-    It "Given SkipLocal switch, sends command but doesn't change PATH" {
-        $path = $env:PATH
-
-        Add-ActionPath 'test path' -SkipLocal
-
-        $env:PATH | Should -Be $path -Because "PATH shouldn't be modified"
-        Should -Invoke Write-Host -ParameterFilter {
-            $Object -eq '::add-path::test path'
-        } -ModuleName GitHubActionsCore
+    Context "When GITHUB_PATH is not set" {
+        BeforeAll {
+            Mock Write-Host { } -ModuleName GitHubActionsCore
+        }
+        It "Sends appropriate workflow command to host and prepends PATH" {
+            Add-ActionPath 'test path'
+    
+            $env:PATH | Should -BeLike "test path$([System.IO.Path]::PathSeparator)*" -Because 'PATH should be also prepended in current scope'
+            Should -Invoke Write-Host -ParameterFilter {
+                $Object -eq '::add-path::test path'
+            } -ModuleName GitHubActionsCore
+        }
+        It "Given SkipLocal switch, sends command but doesn't change PATH" {
+            $path = $env:PATH
+    
+            Add-ActionPath 'test path' -SkipLocal
+    
+            $env:PATH | Should -Be $path -Because "PATH shouldn't be modified"
+            Should -Invoke Write-Host -ParameterFilter {
+                $Object -eq '::add-path::test path'
+            } -ModuleName GitHubActionsCore
+        }
     }
-    AfterEach {
-        [System.Environment]::SetEnvironmentVariable('PATH', $prevPath)
+    Context "When GITHUB_PATH is set" {
+        BeforeEach {
+            $testPath = 'TestDrive:/path-cmd.env'
+            Set-Content $testPath '' -NoNewline
+            $env:GITHUB_PATH = $testPath
+        }
+        It "Sends appropriate workflow command to command file and prepends PATH" {
+            Add-ActionPath 'test path'
+    
+            $env:PATH | Should -BeLike "test path$([System.IO.Path]::PathSeparator)*" -Because 'PATH should be also prepended in current scope'
+            Get-Content $testPath -Raw
+            | Should -BeExactly "test path$([System.Environment]::NewLine)"
+        }
+        It "Sends appropriate workflow command to command file but doesn't change PATH due to -SkipLocal" {
+            $path = $env:PATH
+    
+            Add-ActionPath 'test path' -SkipLocal
+    
+            $env:PATH | Should -Be $path -Because "PATH shouldn't be modified"
+            Get-Content $testPath -Raw
+            | Should -BeExactly "test path$([System.Environment]::NewLine)"
+        }
     }
 }
 Describe 'Set-ActionCommandEcho' {
@@ -144,6 +218,8 @@ Describe 'Set-ActionCommandEcho' {
 }
 Describe 'Set-ActionFailed' {
     BeforeAll {
+        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterAll')]
+        $oldExitCode = [System.Environment]::ExitCode
         Mock Write-Host { } -ModuleName GitHubActionsCore
     }
     BeforeEach {
@@ -162,16 +238,21 @@ Describe 'Set-ActionFailed' {
             $Object -eq "::error::$Expected"
         } -ModuleName GitHubActionsCore
     }
-    AfterEach {
-        [System.Environment]::ExitCode = 0
+    AfterAll {
+        [System.Environment]::ExitCode = $oldExitCode
     }
 }
 Describe 'Get-ActionIsDebug' {
     BeforeAll {
         Mock Write-Host { } -ModuleName GitHubActionsCore
+        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterAll')]
+        $oldEnvRunnerDebug = $env:RUNNER_DEBUG
     }
     BeforeEach {
-        Remove-Item Env:RUNNER_DEBUG -ErrorAction SilentlyContinue
+        $env:RUNNER_DEBUG = $null
+    }
+    AfterAll {
+        $env:RUNNER_DEBUG = $oldEnvRunnerDebug
     }
     It 'Given env var is not set, return false' {
         $result = Get-ActionIsDebug
@@ -192,9 +273,6 @@ Describe 'Get-ActionIsDebug' {
         
         $result | Should -BeExactly $Expected
     }
-    AfterEach {
-        Remove-Item Env:RUNNER_DEBUG -ErrorAction SilentlyContinue
-    }
 }
 Describe 'Write-ActionError' {
     BeforeAll {
@@ -334,4 +412,59 @@ Describe 'Send-ActionCommand' {
             $Object -eq $Expected
         } -ModuleName GitHubActionsCore
     }
-}
\ No newline at end of file
+}
+
+Describe 'Send-ActionFileCommand' {
+    BeforeAll {
+        [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'Used in AfterAll')]
+        $oldGithubTestcmd = $env:GITHUB_TESTCMD
+    }
+    BeforeEach {
+        $testPath = 'TestDrive:/testcmd.env'
+        $env:GITHUB_TESTCMD = $testPath
+    }
+    AfterAll {
+        $env:GITHUB_TESTCMD = $oldGithubTestcmd
+    }
+    Context "When file doesn't exist" {
+        BeforeEach {
+            Remove-Item $testPath -Force -ea:Ignore
+        }
+        It "Given no command ('<value>') throws" -TestCases @(
+            @{ Value = $null }
+            @{ Value = '' }
+        ) {
+            {
+                Send-ActionFileCommand -Command $Value -Message 'foobar'
+            } | Should -Throw "Cannot validate argument on parameter 'Command'. The argument is null or empty.*"
+        }
+        It "Given command for which env var doesn't exist" {
+            $env:GITHUB_TESTCMD = $null
+            {
+                Send-ActionFileCommand -Command TESTCMD -Message 'foobar'
+            } | Should -Throw 'Unable to find environment variable for file command TESTCMD'
+        }
+        It "Given command for which file doesn't exist" {
+            {
+                Send-ActionFileCommand -Command TESTCMD -Message 'foobar'
+            } | Should -Throw 'Missing file at path: *testcmd.env'
+        }
+    }
+    Context 'When file exists' {
+        BeforeEach {
+            Set-Content $testPath '' -NoNewline
+        }
+        It "Given a command with message '<msg>' writes '<expected>' to a file" -TestCases @(
+            @{ Msg = ''; Expected = $null }
+            @{ Msg = 'a'; Expected = $null }
+            @{ Msg = "a `r `n b : c % d"; Expected = $null }
+            @{ Msg = 1; Expected = $null }
+            @{ Msg = $true; Expected = 'true' }
+            @{ Msg = [ordered]@{ a = 1; b = $false }; Expected = '{"a":1,"b":false}' }
+        ) {
+            Send-ActionFileCommand TESTCMD -Message $Msg
+
+            Get-Content $testPath -Raw | Should -BeExactly (($Expected ?? "$Msg") + [System.Environment]::NewLine)
+        }
+    }
+}
diff --git a/lib/GitHubActionsCore/GitHubActionsCore.psm1 b/lib/GitHubActionsCore/GitHubActionsCore.psm1
index 2c1136a..7d2f275 100644
--- a/lib/GitHubActionsCore/GitHubActionsCore.psm1
+++ b/lib/GitHubActionsCore/GitHubActionsCore.psm1
@@ -37,15 +37,23 @@ function Set-ActionVariable {
         [switch]$SkipLocal
     )
     $convertedValue = ConvertTo-ActionCommandValue $Value
-    ## To take effect only in the current action/step
+    ## To take effect in the current action/step
     if (-not $SkipLocal) {
         [System.Environment]::SetEnvironmentVariable($Name, $convertedValue)
     }
 
     ## To take effect for all subsequent actions/steps
-    Send-ActionCommand set-env @{
-        name = $Name
-    } -Message $convertedValue
+    if ($env:GITHUB_ENV) {
+        $delimiter = '_GitHubActionsFileCommandDelimeter_'
+        $eol = [System.Environment]::NewLine
+        $commandValue = "$name<<${delimiter}${eol}${convertedValue}${eol}${delimiter}"
+        Send-ActionFileCommand -Command ENV -Message $commandValue
+    }
+    else {
+        Send-ActionCommand set-env @{
+            name = $Name
+        } -Message $convertedValue
+    }
 }
 
 <#
@@ -93,7 +101,7 @@ function Add-ActionPath {
         [switch]$SkipLocal
     )
 
-    ## To take effect only in the current action/step
+    ## To take effect in the current action/step
     if (-not $SkipLocal) {
         $oldPath = [System.Environment]::GetEnvironmentVariable('PATH')
         $newPath = "$Path$([System.IO.Path]::PathSeparator)$oldPath"
@@ -101,7 +109,12 @@ function Add-ActionPath {
     }
 
     ## To take effect for all subsequent actions/steps
-    Send-ActionCommand add-path $Path
+    if ($env:GITHUB_PATH) {
+        Send-ActionFileCommand -Command PATH -Message $Path
+    }
+    else {
+        Send-ActionCommand -Command add-path -Message $Path
+    }
 }
 
 ## Used to identify inputs from env vars in Action/Workflow context
@@ -539,6 +552,47 @@ function Send-ActionCommand {
     Write-Host $cmdStr
 }
 
+<#
+.SYNOPSIS
+Sends a command to an Action Environment File.
+Equivalent to `core.issueFileCommand(cmd, msg)`.
+.DESCRIPTION
+Appends given message to an Action Environment File.
+.PARAMETER Command
+Command (environment file variable suffix) to send message for.
+.PARAMETER Message
+Message to append.
+.EXAMPLE
+PS> Send-ActionFileCommand ENV 'myvar=value'
+.EXAMPLE
+PS> 'myvar=value', 'myvar2=novalue' | Send-ActionFileCommand ENV
+.LINK
+https://docs.github.com/en/actions/reference/workflow-commands-for-github-actions#environment-files
+#>
+function Send-ActionFileCommand {
+    [CmdletBinding()]
+    param (
+        [Parameter(Position = 0, Mandatory)]
+        [ValidateNotNullOrEmpty()]
+        [string]$Command,
+
+        [Parameter(Position = 1, Mandatory, ValueFromPipeline)]
+        [psobject]$Message
+    )
+    begin {
+        $filePath = [System.Environment]::GetEnvironmentVariable("GITHUB_$Command")
+        if (-not $filePath) {
+            throw "Unable to find environment variable for file command $Command"
+        }
+        if (-not (Test-Path $filePath -PathType Leaf)) {
+            throw "Missing file at path: $filePath"
+        }
+    }
+    process {
+        ConvertTo-ActionCommandValue $Message | Out-File -FilePath $filePath -Append
+    }
+}
+
 ###########################################################################
 ## Internal Implementation
 ###########################################################################
@@ -669,6 +723,7 @@ Get-ActionIsDebug,
 Invoke-ActionGroup,
 Invoke-ActionNoCommandsBlock,
 Send-ActionCommand,
+Send-ActionFileCommand,
 Set-ActionCommandEcho,
 Set-ActionFailed,
 Set-ActionOutput,
diff --git a/test.ps1 b/test.ps1
new file mode 100644
index 0000000..e2b72a3
--- /dev/null
+++ b/test.ps1
@@ -0,0 +1,12 @@
+[CmdletBinding()]
+param (
+    [Parameter()]
+    [switch]
+    $CI = ($env:CI -eq 'true')
+)
+
+if (Get-Module Pester | ? Version -LT '5.1') {
+    Install-Module -Name Pester -Force -SkipPublisherCheck -MinimumVersion '5.1' -PassThru
+        | Import-Module Pester -MinimumVersion '5.1'
+}
+Invoke-Pester -CI:$CI
\ No newline at end of file