treestonemedia · Sep 10, 2019 · Sep 10, 2019 · Sep 10, 2019
diff --git a/README.md b/README.md
@@ -257,6 +257,11 @@ One or more environment variables failed assertions: SESSION_STORE is not an
 allowed value
 ```
 
+It is also possible to define a regex that your environment variable should be.
+```php
+$dotenv->required('FOO')->allowedRegexValues('([[:lower:]]{3})');
+```
+
 ### Comments
 
 You can comment your `.env` file using the `#` character. E.g.

diff --git a/src/Validator.php b/src/Validator.php
@@ -138,6 +138,26 @@ function ($value) use ($choices) {
         );
     }
 
+    /**
+     * Assert that each variable matches the given regular expression
+     *
+     * @param string $regex
+     *
+     * @throws \Dotenv\Exception\ValidationException
+     *
+     * @return \Dotenv\Validator
+     */
+    public function allowedRegexValues($regex)
+    {
+        return $this->assertCallback(
+            function ($value) use ($regex)
+            {
+                return preg_match($regex, $value) == 1 ;
+            },
+            sprintf('does not match given regex %s' , $regex)
+        );
+    }
+
     /**
      * Assert that the callback returns true for each variable.
      *

diff --git a/tests/Dotenv/ValidatorTest.php b/tests/Dotenv/ValidatorTest.php
@@ -31,6 +31,14 @@ public function testDotenvAllowedValues()
         $this->assertTrue(true);
     }
 
+    public function testDotenvallowedRegexValues()
+    {
+        $dotenv = Dotenv::create($this->fixturesFolder);
+        $dotenv->load();
+        $dotenv->required('FOO')->allowedRegexValues('([[:lower:]]{3})');
+        $this->assertTrue(true);
+    }
+
     public function testDotenvAllowedValuesIfPresent()
     {
         $dotenv = Dotenv::create($this->fixturesFolder);