How to run a script task from a bamboo plugin?

I have a task that runs in a bamboo plugin as a external process. I cannot run any commands like 'echo $PATH' , as it throws the error 'executable not found'. I need to run a script task with the external process to do the above. The requirement is to run a script command from a bamboo plugin in a custom task type plugin.

public ExternalProcess Exec(List<String> pLArg, List<String> pLOpt, String sPwd,
           String projectUserId, Map<String, String> variables)
{
   TaskContext pContext = GetContext();
   List<String> pLCmd = new LinkedList<String>();

   pLCmd.add("echo $PATH ");
   return Exec(pLCmd, sPwd);
}