Use dedicated exceptions if unlinking failed for reasons other than the

file not existing

exceptions/MDFailedToDeleteFile.php

@@ -0,0 +1,18 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Reports a failure to create a new directory.
+ */
+final class MDFailedToDeleteFile extends Exception {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'Failed to delete file';
+
+    }
+}

exceptions/MDFilePermissionsException.php

@@ -0,0 +1,18 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Reports a failure due to insufficient permissions in the file system.
+ */
+final class MDFilePermissionsException extends Exception {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'Insufficient file system permissions';
+
+    }
+}

src/MD_STD.php

@@ -110,7 +110,15 @@ public static function mkdir(string $pathname, int $mode = 0775, bool $recursive
     public static function unlink(string $filename):void {
 
         if (\unlink($filename) === false) {
-            throw new MDFileDoesNotExist("Failed to delete: $filename");
+            if (!\is_file($filename)) {
+                throw new MDFileDoesNotExist("Failed to delete $filename, it did not exist");
+            }
+            else if (!\is_writable(dirname($filename))) {
+                throw new MDFilePermissionsException("Failed to delete $filename");
+            }
+            else {
+                throw new MDFailedToDeleteFile("Failed to delete $filename");
+            }
         }
 
     }