The appropriate part of POSIX is: The description of basic regular expression bracket expressions in the Base Definitions volume of IEEE Std 1003.1-2001, Section 9.3.5, RE Bracket Expression shall also apply to the pattern bracket expression, except that the exclamation mark character ( '!' ) shall replace the circumflex character ( '^' ) in its role in a "non-matching list" in the regular expression notation. A bracket expression starting with an unquoted circumflex character produces unspecified results.
http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_13_01 ** Changed in: dpkg (Ubuntu) Status: Unconfirmed => Confirmed -- Undeclared bashism in dpkg.postinst https://launchpad.net/bugs/89207 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
