Solve "make check-per" failed on Lubuntu
diff --git a/examples/sample.makefile.regen b/examples/sample.makefile.regen
index 50551b2..66bec0a 100755
--- a/examples/sample.makefile.regen
+++ b/examples/sample.makefile.regen
@@ -113,7 +113,7 @@
echo ' done; done; fi'
echo " @if test -f sample-${ASN1PDU}-1.per ; then \\"
echo " for f in sample-*-[1-9].per; do \\"
- echo ' pdu=`echo $$f | sed -E -e "s/sample-([A-Za-z-]+)-[0-9].*/\1/"`; \'
+ echo ' pdu=`echo $$f | sed -E -e "s/sample-([A-Za-z-]+)-[0-9].*/\\1/"`; \'
echo ' for b in 1 17 33 980 8192; do \'
echo ' echo "Recoding $$f into DER into XER and back ($$b)..."; \'
echo ' ./${TARGET} -b $$b -p $$pdu -iper -oder $$f > ./.tmp.1.$$$$ || exit 3; \'