show git diff only for interactive session

bin/rpmbph

@@ -373,7 +373,7 @@ if [ "$VENDOR" = "alt" ] && is_gear $SPECDIR ; then
 	git merge $CURBRANCH
 	mv -f $BPSPEC $SPEC
 	# FIXME: Ctrl-\ and q will cancelled less with return error code
-	if ! ( echo "etersoft-build-utils INFO: Please check diff for backported spec:" ; echo "# etersoft-build-utils NOTE: You can press Ctrl-\ before quit for cancel process."; echo ; git diff $USEBRANCH ) | less; then
+	if tty -s && ! ( echo "etersoft-build-utils INFO: Please check diff for backported spec:" ; echo "# etersoft-build-utils NOTE: You can press Ctrl-\ before quit for cancel process."; echo ; git diff $USEBRANCH ) | less; then
 		#git checkout $SPEC $MDISTR
 		#git checkout $CURBRANCH
 		fatal "User cancelled. You are still in $USEBRANCH branch with modified spec"