Support nested variable regex (#250)

Author: C0DE8

src/Loader.php

@@ -272,7 +272,7 @@ protected function resolveNestedVariables($value)
         if (strpos($value, '$') !== false) {
             $loader = $this;
             $value = preg_replace_callback(
-                '/\${([a-zA-Z0-9_]+)}/',
+                '/\${([a-zA-Z0-9_.]+)}/',
                 function ($matchedPatterns) use ($loader) {
                     $nestedVariable = $loader->getEnvironmentVariable($matchedPatterns[1]);
                     if ($nestedVariable === null) {

tests/Dotenv/DotenvTest.php

@@ -139,6 +139,8 @@ public function testDotenvNestedEnvironmentVars()
         $this->assertSame('{$NVAR1} {$NVAR2}', $_ENV['NVAR3']); // not resolved
         $this->assertSame('Hello World!', $_ENV['NVAR4']);
         $this->assertSame('$NVAR1 {NVAR2}', $_ENV['NVAR5']); // not resolved
+        $this->assertSame('Special Value', $_ENV['N.VAR6']); // new '.' (dot) in var name
+        $this->assertSame('Special Value', $_ENV['NVAR7']);  // nested '.' (dot) variable
     }
 
     /**

tests/fixtures/env/nested.env

@@ -3,3 +3,5 @@ NVAR2="World!"
 NVAR3="{$NVAR1} {$NVAR2}"
 NVAR4="${NVAR1} ${NVAR2}"
 NVAR5="$NVAR1 {NVAR2}"
+N.VAR6="Special Value"
+NVAR7="${N.VAR6}"