Run shellcheck in addition to the tests

.travis.yml

@@ -1,7 +1,15 @@
 language: sh
+
 script: |
     PATH=$PATH:$TRAVIS_BUILD_DIR make test
+
 addons:
   apt:
+    sources:
+    - debian-sid    # Grab shellcheck from the Debian repo (o_O)
     packages:
     - socat
+    - shellcheck
+
+notifications:
+  email: false

Makefile

@@ -10,6 +10,9 @@ install : $(PROGRAM)
 test:
 	make -C tests all
 
+shellcheck:
+	make -C tests shellcheck
+
 readme:
 	@ printf '<!---\nThis README file is generated. Changes will be overwritten.\n-->\n' > README.md
 	@ printf '[![Build Status](https://travis-ci.org/whiteinge/ok.sh.svg?branch=master)](https://travis-ci.org/whiteinge/ok.sh)\n' >> README.md

tests/Makefile

@@ -1,4 +1,7 @@
-all: test
+all: test shellcheck
 
 test:
 	./run_tests.sh
+
+shellcheck:
+	shellcheck -e SC2155 ../ok.sh