https://bugs.gentoo.org/775158
--- a/configure.ac
+++ b/configure.ac
@@ -11,7 +11,7 @@ AC_DEFINE_DIR(LOCALSTATEDIR, localstatedir)
 dnl Perl stuff
 AC_PATH_PROG([PERL], [perl])
 eval `$PERL -V:startperl`
-if test "${startperl:0:1}" = "#" ; then
+if test "$(printf %.1s "$startperl")" = "#" ; then
   startperl="\\$startperl"
 fi
 AC_SUBST(PERL_SHEBANG, $startperl)