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  • Is it sufficient for the first command to have no process? What about ls | ( /bin/echo hi; /bin/cat ) which runs echo and cat as separate processes, but cat still reads stdin from ls instead of /bin/echo? Commented Aug 17, 2012 at 13:31
  • If the first command is not a builtin, the shell will have to do an extra fork. But that doesn't matter, because children inherit their parents' file descriptors. Commented Aug 17, 2012 at 13:35
  • Thanks! To elaborate on your answer even further: I checked the cd's definition in IEEE Std 1003.1-2008. In the "STDIN" and "STDOUT" sections it says both streams are (almost always) not used by cd. Commented Aug 17, 2012 at 13:42