+## Our test case should use the $(...) POSIX form for command substitution,
+## rather than the older `...` form.
+## The point of ignoring text on here-documents is that we want to exempt
+## Makefile.am rules, configure.ac code and helper shell script created and
+## used by out shell scripts, because Autoconf (as of version 2.69) does not
+## yet ensure that $CONFIG_SHELL will be set to a proper POSIX shell.
+sc_tests_command_subst:
+ @found=false; \
+ scan () { \
+ sed -n -e '/^#/d' \
+ -e '/<<.*END/,/^END/b' -e '/<<.*EOF/,/^EOF/b' \
+ -e 's/\\`/\\{backtick}/' \
+ -e "s/[^\\]'\([^']*\`[^']*\)*'/'{quoted-text}'/g" \
+ -e '/`/p' $$*; \
+ }; \
+ for file in $(xtests); do \
+ res=`scan $$file`; \
+ if test -n "$$res"; then \
+ echo "$$file:$$res"; \
+ found=true; \
+ fi; \
+ done; \
+ if $$found; then \
+ echo 'Use $$(...), not `...`, for command substitutions.' >&2; \
+ exit 1; \
+ fi
+