diff --git a/Makefile b/Makefile
index 0f05c93..4c54203 100644
--- a/Makefile
+++ b/Makefile
@@ -14,9 +14,7 @@ default: lvspec.pdf
 # outputs a version string to uniquely identify the document revision
 # TODO: use tag name if matches current commit
 verstr.tex:
-	git log -n1 --format=%h | tr -d '\n' > verstr.tex
-	test -z "$$( git status -s | grep -v '^?? ' )" \
-		|| echo -n '-dirty' >> verstr.tex
+	verstr >$@
 
 clean:
 	rm -f *.pdf
diff --git a/verstr b/verstr
new file mode 100755
index 0000000..08e6a02
--- /dev/null
+++ b/verstr
@@ -0,0 +1,10 @@
+#!/bin/sh
+#
+# Generates version string
+
+# output current shortref
+git log -n1 --format=%h | tr -d '\n'
+
+# if we have uncommitted changes, then append with -dirty
+test -z "$$( git status -s | grep -v '^?? ' )" \
+  || echo -n '-dirty'