Run shellcheck on Travis CI

.travis.yml

@@ -52,6 +52,9 @@ matrix:
       language: node_js
       python: null
       node_js: "lts/*"
+    - os: linux
+      env: TESTENV=shellcheck
+      services: docker
   fast_finish: true
 
 cache:

scripts/dev/ci/travis_run.sh

@@ -14,6 +14,16 @@ elif [[ $TESTENV == eslint ]]; then
     # travis env
     cd qutebrowser/javascript || exit 1
     eslint --color --report-unused-disable-directives .
+elif [[ $TESTENV == shellcheck ]]; then
+    dev_scripts=$( find scripts/dev/ -name '*.sh' -print0 | xargs -0 )
+    # false positive: we are using 'find -exec +'
+    # shellcheck disable=SC2038
+    userscripts=$( find misc/userscripts/ -type f -exec grep -lE '[/ ][bd]ash$|[/ ]sh$|[/ ]ksh$' {} + | xargs )
+    IFS=" " read -r -a scripts <<< "$dev_scripts $userscripts"
+    docker run \
+           -v "$PWD:/outside" \
+	   -w /outside \
+           koalaman/shellcheck:stable "${scripts[@]}"
 else
     args=()
     [[ $TRAVIS_OS_NAME == osx ]] && args=('--qute-bdd-webengine' '--no-xvfb')