Extend upload and subsequent 'dot sourcing' of env vars to std PS command

* Wrap funcs to flatten and upload env vars with new func prepareEnvVars.
  While the wrapped funcs could be combined, keeping them separate
  simplifies testing.
* Configure/refactor std and elevated PS to use new funcs to prepare,
  upload and dot source env vars.
* Dot sourcing the env vars in this way avoids the need to embed them
  directly in the command string. This avoids the need to escape the env
  vars to ensure the command string is correctly parsed.
* Characters within the env vars that are special to PS (such as $'s
  and backticks) will still need to be escaped to allow them to be
  correctly interpreted by PS.
* The std and elevated PS commands now inject env vars into the remote
  env via the same mechanism. This ensures consistent behaviour across the
  two command types.

Fixes #5471

provisioner/powershell/provisioner.go

@@ -113,7 +113,7 @@ func (p *Provisioner) Prepare(raws ...interface{}) error {
 	}
 
 	if p.config.EnvVarFormat == "" {
-		p.config.EnvVarFormat = `$env:%s=\"%s\"; `
+		p.config.EnvVarFormat = `$env:%s="%s"; `
 	}
 
 	if p.config.ElevatedEnvVarFormat == "" {
@@ -121,7 +121,7 @@ func (p *Provisioner) Prepare(raws ...interface{}) error {
 	}
 
 	if p.config.ExecuteCommand == "" {
-		p.config.ExecuteCommand = `powershell -executionpolicy bypass "& { if (Test-Path variable:global:ProgressPreference){$ProgressPreference='SilentlyContinue'};{{.Vars}}&'{{.Path}}';exit $LastExitCode }"`
+		p.config.ExecuteCommand = `powershell -executionpolicy bypass "& { if (Test-Path variable:global:ProgressPreference){$ProgressPreference='SilentlyContinue'};. {{.Vars}}; &'{{.Path}}';exit $LastExitCode }"`
 	}
 
 	if p.config.ElevatedExecuteCommand == "" {
@@ -331,6 +331,19 @@ func (p *Provisioner) retryable(f func() error) error {
 	}
 }
 
+// Enviroment variables required within the remote environment are uploaded within a PS script and
+// then enabled by 'dot sourcing' the script immediately prior to execution of the main command
+func (p *Provisioner) prepareEnvVars(elevated bool) (envVarPath string, err error) {
+	// Collate all required env vars into a plain string with required formatting applied
+	flattenedEnvVars := p.createFlattenedEnvVars(elevated)
+	// Create a powershell script on the target build fs containing the flattened env vars
+	envVarPath, err = p.uploadEnvVars(flattenedEnvVars)
+	if err != nil {
+		return "", err
+	}
+	return
+}
+
 func (p *Provisioner) createFlattenedEnvVars(elevated bool) (flattened string) {
 	flattened = ""
 	envVars := make(map[string]string)
@@ -367,6 +380,19 @@ func (p *Provisioner) createFlattenedEnvVars(elevated bool) (flattened string) {
 	return
 }
 
+func (p *Provisioner) uploadEnvVars(flattenedEnvVars string) (envVarPath string, err error) {
+	// Upload all env vars to a powershell script on the target build file system
+	envVarReader := strings.NewReader(flattenedEnvVars)
+	uuid := uuid.TimeOrderedUUID()
+	envVarPath = fmt.Sprintf(`${env:SYSTEMROOT}\Temp\packer-env-vars-%s.ps1`, uuid)
+	log.Printf("Uploading env vars to %s", envVarPath)
+	err = p.communicator.Upload(envVarPath, envVarReader, nil)
+	if err != nil {
+		return "", fmt.Errorf("Error uploading ps script containing env vars: %s", err)
+	}
+	return
+}
+
 func (p *Provisioner) createCommandText() (command string, err error) {
 	// Return the interpolated command
 	if p.config.ElevatedUser == "" {
@@ -377,12 +403,15 @@ func (p *Provisioner) createCommandText() (command string, err error) {
 }
 
 func (p *Provisioner) createCommandTextNonPrivileged() (command string, err error) {
-	// Create environment variables to set before executing the command
-	flattenedEnvVars := p.createFlattenedEnvVars(false)
+	// Prepare everything needed to enable the required env vars within the remote environment
+	envVarPath, err := p.prepareEnvVars(false)
+	if err != nil {
+		return "", err
+	}
 
 	p.config.ctx.Data = &ExecuteCommandTemplate{
-		Vars: flattenedEnvVars,
 		Path: p.config.RemotePath,
+		Vars: envVarPath,
 	}
 	command, err = interpolate.Render(p.config.ExecuteCommand, &p.config.ctx)
 
@@ -395,17 +424,10 @@ func (p *Provisioner) createCommandTextNonPrivileged() (command string, err erro
 }
 
 func (p *Provisioner) createCommandTextPrivileged() (command string, err error) {
-	// Can't double escape the env vars, lets create shiny new ones
-	flattenedEnvVars := p.createFlattenedEnvVars(true)
-	// Need to create a mini ps1 script containing all of the environment variables we want;
-	// we'll be dot-sourcing this later
-	envVarReader := strings.NewReader(flattenedEnvVars)
-	uuid := uuid.TimeOrderedUUID()
-	envVarPath := fmt.Sprintf(`${env:SYSTEMROOT}\Temp\packer-env-vars-%s.ps1`, uuid)
-	log.Printf("Uploading env vars to %s", envVarPath)
-	err = p.communicator.Upload(envVarPath, envVarReader, nil)
+	// Prepare everything needed to enable the required env vars within the remote environment
+	envVarPath, err := p.prepareEnvVars(true)
 	if err != nil {
-		return "", fmt.Errorf("Error preparing elevated powershell script: %s", err)
+		return "", err
 	}
 
 	p.config.ctx.Data = &ExecuteCommandTemplate{