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$? contains the return status for subshells, commands, pipelines, functions, etc. From the man page, under Special Parameters :

  ?     Expands to the exit status of the most recently executed foreground pipeline.

  $ foo="$(echo foobar ; exit 3)" ; ret=$? ; echo "output: $foo" ; echo "return status: $ret"
  output: foobar
  return status: 3

Also, PIPESTATUS is an array with the return status from each command in a pipeline.