Fix shellcheck warnings and errors (#47)

* Add CI

* Fix all warnings and errors from shellcheck

Author: guillaumealgis

.github/workflows/main.yml

@@ -0,0 +1,15 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: shellcheck
+      uses: azohra/[email protected]