diff --git a/tools/binarchs.sh b/tools/binarchs.sh
new file mode 100755
index 0000000000000000000000000000000000000000..20d8c31a3b2ad7adac1c6f92aba5d6cfc4af41fd
--- /dev/null
+++ b/tools/binarchs.sh
@@ -0,0 +1,11 @@
+#! /bin/bash
+
+# Get architectures for system programs.
+# NOTE: Currently needed to build 'which' on 10.4.
+
+REFPROG="${1:-/usr/bin/true}"
+
+ARCHS="$(file $REFPROG | grep ' executable ' | sed 's|.* executable ||')"
+ARCHFLAGS="$(for a in $ARCHS; do echo -n ' -arch' $a; done)"
+
+echo $ARCHFLAGS