diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
new file mode 100644
index 0000000..10d2580
--- /dev/null
+++ b/.github/workflows/CI.yml
@@ -0,0 +1,33 @@
+name: CI
+
+on: [push, pull_request, workflow_dispatch]
+
+jobs:
+  run-tests:
+    if: github.repository_owner == 'olemorud'
+
+    permissions:
+      contents: read
+    
+    runs-on: ubuntu-latest
+    
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: npm install
+        run: npm ci
+
+      - name: Run unit tests
+        run: npm run test
+
+      - name: Apply problem matcher
+        uses: ./
+        with:
+          build-directory: build/
+      
+      - name: Test problem matcher
+        run: |
+          ls
+          cat dist/gcc_matcher.json
+          cp -r test build
+          gcc -Wall -Wextra -O0 build/generate_warnings.c
\ No newline at end of file
diff --git a/action.yml b/action.yml
index a96d57e..4a0261a 100644
--- a/action.yml
+++ b/action.yml
@@ -9,10 +9,9 @@ branding:
   color: yellow
 
 inputs:
-  root:
+  build-directory:
     description: 'base directory for build, e.g. /workdir/build'
-    required: false
-    default: ''
+    required: true
 
 runs:
   using: 'node16'
diff --git a/dist/gcc_matcher.jsontemplate b/dist/gcc_matcher.jsontemplate
index 0c338d9..d157a38 100644
--- a/dist/gcc_matcher.jsontemplate
+++ b/dist/gcc_matcher.jsontemplate
@@ -4,7 +4,7 @@
             "owner": "gcc-problem-matcher",
             "pattern": [
                 {
-                    "regexp": "^${{ BASE }}\/?(.*?):(\\d+):(\\d*):?\\s+(?:fatal\\s+)?(warning|error):\\s+(.*)$",
+                    "regexp": "^.*?${{ BASE }}\/?(.*?):(\\d+):(\\d*):?\\s+(?:fatal\\s+)?(warning|error):\\s+(.*)$",
                     "file": 1,
                     "line": 2,
                     "column": 3,
diff --git a/dist/index.js b/dist/index.js
index b6ef0f0..18b78d9 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -2845,32 +2845,50 @@ const path = __nccwpck_require__(17);
 const fs = __nccwpck_require__(561);
 const core = __nccwpck_require__(127);
 
-// C:\Users\ => C\:\\Users\\
+// escapeRegExp :: string => string
+// escape all characters with special meanings in regexp
 const escapeRegExp = (s) =>
-	s.replace(/[:.*+?^${}()|\/[\]\\]/g, "\\$&");
+	s.replace(/[/\-^$*+?.()|[\]{}]/g, "\\$&");
 
-
-// ${{ key }}, ${{var}}, ${{ aggqq43g3qg4 }}
+// variable :: string => RegExp
+// create regex to match ${{ key }}
 const variable = (key) =>
 	new RegExp("\\${{\\s*?" + key + "\\s*?}}", "g");
 
-
-// default value set in /action.yml
-const root = core.getInput('root', { required: false });
-
+// templatePath :: string
 const templatePath = __nccwpck_require__.ab + "gcc_matcher.jsontemplate";
 
-const parsed = 
-	fs.readFileSync(__nccwpck_require__.ab + "gcc_matcher.jsontemplate", "ascii")
-		.replace(variable("BASE"), escapeRegExp(root));
-
+// matcherPath :: string
 const matcherPath = __nccwpck_require__.ab + "gcc_matcher.json";
 
-fs.writeFileSync(__nccwpck_require__.ab + "gcc_matcher.json", parsed);
+// rootdir :: string
+const rootdir = () =>
+	core.getInput('build-directory', {required: false}) || "/build";
 
-console.log('::add-matcher::' + matcherPath);
+// parse :: IO() => IO() => Error | null
+const parse = (templatePath) => (matcherPath) => {
+	const r = rootdir();
 
-/* for testing */ 
+	console.log(r);
+
+	const content = fs.readFileSync(templatePath, 'utf-8');
+
+	const parsed = content.replace(variable("BASE"), escapeRegExp(rootdir()));
+
+	fs.writeFileSync(matcherPath, parsed);
+
+	console.log('::add-matcher::' + matcherPath);
+}
+
+// main:
+try {
+	parse(__nccwpck_require__.ab + "gcc_matcher.jsontemplate")(__nccwpck_require__.ab + "gcc_matcher.json");
+} catch (err) {
+	core.setFailed(`Action failed with error ${err}`)
+}
+
+
+// for testing
 exports.escapeRegExp = escapeRegExp
 exports.variable = variable;
 })();
diff --git a/src/gcc_matcher.jsontemplate b/src/gcc_matcher.jsontemplate
index 0c338d9..d157a38 100644
--- a/src/gcc_matcher.jsontemplate
+++ b/src/gcc_matcher.jsontemplate
@@ -4,7 +4,7 @@
             "owner": "gcc-problem-matcher",
             "pattern": [
                 {
-                    "regexp": "^${{ BASE }}\/?(.*?):(\\d+):(\\d*):?\\s+(?:fatal\\s+)?(warning|error):\\s+(.*)$",
+                    "regexp": "^.*?${{ BASE }}\/?(.*?):(\\d+):(\\d*):?\\s+(?:fatal\\s+)?(warning|error):\\s+(.*)$",
                     "file": 1,
                     "line": 2,
                     "column": 3,
diff --git a/src/index.js b/src/index.js
index 04c6728..bae4398 100644
--- a/src/index.js
+++ b/src/index.js
@@ -5,7 +5,7 @@ const core = require('@actions/core');
 // escapeRegExp :: string => string
 // escape all characters with special meanings in regexp
 const escapeRegExp = (s) =>
-	s.replace(/[:.*+?^${}()|\/[\]\\]/g, "\\$&");
+	s.replace(/[/\-^$*+?.()|[\]{}]/g, "\\$&");
 
 // variable :: string => RegExp
 // create regex to match ${{ key }}
@@ -18,25 +18,31 @@ const templatePath = path.join(__dirname, "gcc_matcher.jsontemplate");
 // matcherPath :: string
 const matcherPath = path.join(__dirname, "gcc_matcher.json");
 
-// parse :: IO => IO => Error | null
+// rootdir :: string
+const rootdir = () =>
+	core.getInput('build-directory', {required: false});
+
+// parse :: IO() => IO() => Error | null
 const parse = (templatePath) => (matcherPath) => {
-	fs.readFile(templatePath, 'utf-8', (err, content) => {
-		if (err) throw err;
+	const r = rootdir();
 
-		const root = core.getInput('root', { required: false });
+	console.log(r);
 
-		const parsed = content.replace(variable("BASE"), escapeRegExp(root));
+	const content = fs.readFileSync(templatePath, 'utf-8');
 
-		fs.writeFile(matcherPath, parsed, (err) => {
-			if (err) throw err;
+	const parsed = content.replace(variable("BASE"), escapeRegExp(rootdir()));
 
-			console.log('::add-matcher::' + matcherPath);
-		});
-	});
+	fs.writeFileSync(matcherPath, parsed);
+
+	console.log('::add-matcher::' + matcherPath);
 }
 
 // main:
-parse(templatePath)(matcherPath);
+try {
+	parse(templatePath)(matcherPath);
+} catch (err) {
+	core.setFailed(`Action failed with error ${err}`)
+}
 
 
 // for testing
diff --git a/test/generate_warnings.c b/test/generate_warnings.c
new file mode 100644
index 0000000..10a55cb
--- /dev/null
+++ b/test/generate_warnings.c
@@ -0,0 +1,20 @@
+#include <limits.h>
+
+int bad_code(float n) {
+
+    int small[3];
+
+    char index = 10;
+
+    int x = small[index];
+
+    double promoted = 3.14159 * n * n;
+
+    return bad_code(x);
+}
+
+
+int main() {
+
+    printf("%s %s", bad_code(1.0f));
+}
\ No newline at end of file