moved the logic to provision method

provisioner/shell/provisioner.go

@@ -66,6 +66,9 @@ type Config struct {
 	// name of the tmp environment variable file, if UseEnvVarFile is true
 	envVarFile string
 
+	// If user provided a shebang for inline scripts
+	inlineShebangDefined bool
+
 	ctx interpolate.Context
 }
 
@@ -112,16 +115,9 @@ func (p *Provisioner) Prepare(raws ...interface{}) error {
 	}
 
 	if p.config.InlineShebang == "" {
-		if p.config.Inline != nil && len(p.config.Inline) > 0 && strings.HasPrefix(p.config.Inline[0], "#!") {
-			newLineIndex := strings.Index(p.config.Inline[0], "\n")
-			if newLineIndex == -1 {
-				newLineIndex = len(p.config.Inline[0])
-			}
-			firstLine := strings.TrimRight(p.config.Inline[0][:newLineIndex], "\r")
-			p.config.InlineShebang = strings.TrimPrefix(firstLine, "#!")
-		} else {
-			p.config.InlineShebang = "/bin/sh -e"
-		}
+		p.config.InlineShebang = "/bin/sh -e"
+	} else {
+		p.config.inlineShebangDefined = true
 	}
 
 	if p.config.StartRetryTimeout == 0 {
@@ -212,13 +208,22 @@ func (p *Provisioner) Provision(ctx context.Context, ui packersdk.Ui, comm packe
 
 		// Write our contents to it
 		writer := bufio.NewWriter(tf)
-		_, _ = writer.WriteString(fmt.Sprintf("#!%s\n", p.config.InlineShebang))
+		var shebangWritten bool
 		for _, command := range p.config.Inline {
 			p.config.ctx.Data = generatedData
 			command, err := interpolate.Render(command, &p.config.ctx)
 			if err != nil {
 				return fmt.Errorf("Error interpolating Inline: %s", err)
 			}
+			if !shebangWritten {
+				// If the user has defined an inline shebang, use that.
+				// Or If command does not start with a shebang, use the default shebang.
+				// else command already has a shebang, so do not write it.
+				if p.config.inlineShebangDefined || !strings.HasPrefix(command, "#!") {
+					_, _ = writer.WriteString(fmt.Sprintf("#!%s\n", p.config.InlineShebang))
+				}
+				shebangWritten = true
+			}
 			if _, err := writer.WriteString(command + "\n"); err != nil {
 				return fmt.Errorf("Error preparing shell script: %s", err)
 			}