knit_lessons.sh: require 2 inputs exactly

diff --git a/bin/knit_lessons.sh b/bin/knit_lessons.sh
index 194f12421a6d1fd64a7ee2b367bbcf776953da05..141c136adce04042732d19eb416bc915e57e2717 100755 (executable)
--- a/bin/knit_lessons.sh
+++ b/bin/knit_lessons.sh
@@ -3,6 +3,6 @@
 # Only try running R to translate files if there are some files present.
 # The Makefile passes in the names of files.
 
-if [ $# -ne 0 ] ; then
+if [ $# -eq 2 ] ; then
     Rscript -e "source('bin/generate_md_episodes.R')" "$@"
 fi