https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102664
--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> --- https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Limitations-of-Usual-Tools.html#index-g_t_0040command_007bexpr_007d-1813 The expr match regex should not start with ^ (that is implied anyway, and some versions of expr don't like it)
