diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..1d52e07
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,19 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    name: Test verify-changed-files
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: shellcheck
+        uses: reviewdog/action-shellcheck@v1
diff --git a/action.yml b/action.yml
index edc4b80..ee0ddc6 100644
--- a/action.yml
+++ b/action.yml
@@ -7,9 +7,8 @@ inputs:
     required: true
     default: ${{ github.token }}
   files:
-    description: Comma separated list of files to check for changes.
-    required: false
-    default: ''
+    description: List of files to check for changes.
+    required: true
 runs:
   using: 'docker'
   image: 'Dockerfile'
diff --git a/entrypoint.sh b/entrypoint.sh
index a299a67..e7635f4 100755
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -2,14 +2,18 @@
 
 set -e
 
-GITHUB_TOKEN=$1
 FILES=$2
 
-echo "Formatting filenames..."
-EXPECTED_FILES="$(printf $(echo ${FILES} | sed 's| ||g' | sed 's/,/|/g'))"
+CHANGED_FILES=() 
 
-echo "Checking changes for \"${EXPECTED_FILES}\"... "
-CHANGED_FILES=$(git diff --diff-filter=ACM --name-only | grep -E "(${EXPECTED_FILES})" || true)
+for path in ${FILES}
+do
+   echo "Checking for file changes: \"${path}\"..."
+   MODIFIED_FILE=$(git diff --diff-filter=ACM --name-only | grep -E "(${path})" || true)
+   if [[ -n ${MODIFIED_FILE} ]]; then
+     CHANGED_FILES+=("${path}")
+   fi
+done
 
 if [[ -z ${CHANGED_FILES} ]]; then
   echo "::set-output name=files_changed::false"