This issue occurs due to your locale; you can override your locale's sort order using the LC_COLLATE variable.
$ locale | grep LC_COLLATE LC_COLLATE=C $ printf ".bb\ncc\n.dd\naa" | sort .bb .dd aa cc $ printf ".bb\ncc\n.dd\naa" | LC_COLLATE=en_US sort aa .bb cc .dd - Josh Triplett
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