diff --git a/bin/sub.js b/bin/sub.js
index 02abeff..bf97af9 100644
--- a/bin/sub.js
+++ b/bin/sub.js
@@ -14,16 +14,17 @@ exports.main = async() => {
 
   const { isdir } = result;
 
-  if (isdir === 'd') {
-    const dirRes = await ifdir.getdir();
-    const { dirname } = dirRes;
-    create.createdir(dirname);
-    console.log(
-      chalk.blue('Directory created successfully') + chalk.red('!!!')
-    );
-    return 0;
-  }
-  if (isdir === 'f') {
+  // regex to check whether input string is file or directory
+  var isValid = (function(){
+    var rg1 = /^[^\\/:\*\?"<>\|]+$/; // forbidden characters \ / : * ? " < > |
+    var rg2 = /^\./; // cannot start with dot (.)
+    var rg3 = /^(nul|prn|con|lpt[0-9]|com[0-9])(\.|$)/i; // forbidden file names
+    return function isValid(fname){
+      return rg1.test(fname) && !rg2.test(fname) && !rg3.test(fname);
+    };
+  })();
+
+  if (isValid(isdir) === true){
     const input = await question.questions();
     // console.log(input);
     const { filename, extension } = input;
@@ -33,6 +34,35 @@ exports.main = async() => {
 
     return 0;
   }
+
+  if (isValid(isdir) === false){
+    const dirRes = await ifdir.getdir();
+    const { dirname } = dirRes;
+    create.createdir(dirname);
+    console.log(
+      chalk.blue('Directory created successfully') + chalk.red('!!!'),
+    );
+    return 0;
+  }
+  // if (isdir === 'd') {
+  //   const dirRes = await ifdir.getdir();
+  //   const { dirname } = dirRes;
+  //   create.createdir(dirname);
+  //   console.log(
+  //     chalk.blue('Directory created successfully') + chalk.red('!!!'),
+  //   );
+  //   return 0;
+  // } if (isdir === 'f') {
+  //   const input = await question.questions();
+  //   // console.log(input);
+  //   const { filename, extension } = input;
+  //   // console.log(filename);
+  //   create.create(filename, extension);
+  //   console.log(chalk.blue('File created successfully') + chalk.red('!!!'));
+
+  //   return 0;
+  // }
+
   if (isdir === 'dld') {
     func.deletedirec();
   } else if (isdir === 'df') {
diff --git a/tmp b/tmp
new file mode 100644
index 0000000..e69de29