Fix interactive shell command keepalive task

These stopped working at some point because the $(...) commands were
getting evaluated immediately instead of within the for loop. Avoiding
the double shell wrapper for buildpacks fixes this.

app/app.go

@@ -30,8 +30,6 @@ var maxLifetime = 12 * 60 * 60
 var waitForConnect = 60
 
 var ShellBackgroundCommand = []string{
-	"/bin/sh",
-	"-c",
 	strings.Join([]string{
 		"STOP=$(($(date +%s)+" + fmt.Sprintf("%d", maxLifetime) + "))",
 		// Give user time to connect

cmd/db.go

@@ -79,7 +79,7 @@ var dbShellCmd = &cobra.Command{
 		checkErr(err)
 		family, exec, err := a.DBShellTaskInfo()
 		checkErr(err)
-		StartInteractiveShell(a, family, aws.String(fmt.Sprintf("entrypoint.sh %s", *exec)), &ecs.TaskOverride{})
+		StartInteractiveShell(a, family, aws.String(fmt.Sprintf("entrypoint.sh %s", *exec)), []string{"/bin/sh", "-c"}, &ecs.TaskOverride{})
 	},
 }
 

cmd/shell.go

@@ -58,10 +58,10 @@ func WaitForTaskRunning(a *app.App, task *ecs.Task) error {
 	return nil
 }
 
-func StartInteractiveShell(a *app.App, taskFamily, shellCmd *string, taskOverride *ecs.TaskOverride) {
+func StartInteractiveShell(a *app.App, taskFamily, shellCmd *string, taskCommandPrefix []string, taskOverride *ecs.TaskOverride) {
 	task, err := a.StartTask(
 		taskFamily,
-		app.ShellBackgroundCommand,
+		append(taskCommandPrefix, app.ShellBackgroundCommand...),
 		taskOverride,
 		false,
 	)
@@ -128,7 +128,7 @@ func interactiveCmd(a *app.App, cmd string) {
 	checkErr(a.ValidateECSTaskSize(*size))
 	isBuildpack := *buildSystem == "buildpacks" || *buildSystem == ""
 	exec := cmd
-	if isBuildpack && !shellRoot{
+	if isBuildpack && !shellRoot {
 		exec = fmt.Sprintf("su --preserve-environment --pty --command '/cnb/lifecycle/launcher %s' heroku", cmd)
 	} else if !isBuildpack && shellRoot {
 		checkErr(fmt.Errorf("--root is only supported on the buildpack build system"))
@@ -170,7 +170,12 @@ func interactiveCmd(a *app.App, cmd string) {
 		err = a.ConnectToEcsSession(ecsSession)
 		checkErr(err)
 	}
-	StartInteractiveShell(a, taskFamily, &exec, &ecs.TaskOverride{
+	var taskCommandPrefix []string
+	if !isBuildpack {
+		// buildpacks already wrap commands in `bash -c`
+		taskCommandPrefix = []string{"/bin/sh", "-c"}
+	}
+	StartInteractiveShell(a, taskFamily, &exec, taskCommandPrefix, &ecs.TaskOverride{
 		Cpu:    aws.String(fmt.Sprintf("%d", size.CPU)),
 		Memory: aws.String(fmt.Sprintf("%d", size.Memory)),
 	})