+# find_tool ENVVAR NAMES...
+# -------------------------
+# Search for a required program. Use the value of ENVVAR, if set,
+# otherwise find the first of the NAMES that can be run (i.e.,
+# supports --version). If found, set ENVVAR to the program name,
+# die otherwise.
+#
+# FIXME: code duplication, see also bootstrap.
+find_tool ()
+{
+ find_tool_envvar=$1
+ shift
+ find_tool_names=$@
+ eval "find_tool_res=\$$find_tool_envvar"
+ if test x"$find_tool_res" = x; then
+ for i
+ do
+ if ($i --version </dev/null) >/dev/null 2>&1; then
+ find_tool_res=$i
+ break
+ fi
+ done
+ else
+ find_tool_error_prefix="\$$find_tool_envvar: "
+ fi
+ test x"$find_tool_res" != x \
+ || die "one of these is required: $find_tool_names"
+ ($find_tool_res --version </dev/null) >/dev/null 2>&1 \
+ || die "${find_tool_error_prefix}cannot run $find_tool_res --version"
+ eval "$find_tool_envvar=\$find_tool_res"
+ eval "export $find_tool_envvar"
+}
+
+## ------ ##
+## Main. ##
+## ------ ##
+
+# Requirements: everything required to bootstrap your package, plus
+# these.
+find_tool CVS cvs
+find_tool GIT git
+find_tool RSYNC rsync
+find_tool XARGS gxargs xargs
+