options.modified added.

options.modified value is true, the target file exists, the file's modification date is compared. the target is smaller than the modified date of the file from the source file's modification date, the copy operation is performed. target file's modification date is set.

lib/ncp.js

@@ -1,5 +1,6 @@
 var fs = require('fs'),
-    path = require('path');
+    path = require('path'),
+    util = require('util');
 
 const modern = /^v0\.1\d\.\d+/.test(process.version);
 
@@ -21,6 +22,7 @@ function ncp (source, dest, options, callback) {
       rename = options.rename,
       transform = options.transform,
       clobber = options.clobber !== false,
+      modified = options.modified,
       dereference = options.dereference,
       errs = null,
       eventName = modern ? 'finish' : 'close',
@@ -68,6 +70,8 @@ function ncp (source, dest, options, callback) {
       // We need to get the mode from the stats object and preserve it.
       item.name = source;
       item.mode = stats.mode;
+      item.mtime = stats.mtime; //modified time
+      item.atime = stats.atime; //access time
 
       if (stats.isDirectory()) {
         return onDir(item);
@@ -95,7 +99,17 @@ function ncp (source, dest, options, callback) {
         rmFile(target, function () {
           copyFile(file, target);
         });
-      } else {
+      }
+      if (modified) {
+        var stat = dereference ? fs.stat : fs.lstat;
+        stat(target, function(err, stats) {
+            //if souce modified time greater to target modified time copy file
+            if (file.mtime.getTime()>stats.mtime.getTime())
+                copyFile(file, target);
+            else return cb();
+        });
+      }
+      else {
         return cb();
       }
     });
@@ -115,7 +129,14 @@ function ncp (source, dest, options, callback) {
         readStream.pipe(writeStream);
       });
     }
-    writeStream.once(eventName, cb);
+    writeStream.once(eventName, function() {
+        if (modified) {
+            //target file modified date sync.
+            fs.utimesSync(target, file.atime, file.mtime);
+            cb();
+        }
+        else cb();
+    });
   }
 
   function rmFile(file, done) {

test/modified-files/out/a

@@ -0,0 +1 @@
+test2

test/modified-files/src/a

@@ -0,0 +1 @@
+test3

test/ncp.js

@@ -5,9 +5,11 @@ var assert = require('assert'),
     path = require('path'),
     rimraf = require('rimraf'),
     readDirFiles = require('read-dir-files'),
+    util = require('util'),
     ncp = require('../').ncp;
 
 
+
 describe('ncp', function () {
   describe('regular files and directories', function () {
     var fixtures = path.join(__dirname, 'regular-fixtures'),
@@ -166,4 +168,30 @@ describe('ncp', function () {
       });
     });
   });
-});
+
+  describe('modified files copies', function () {
+      var fixtures = path.join(__dirname, 'modified-files'),
+          src = path.join(fixtures, 'src'),
+          out = path.join(fixtures, 'out');
+
+      it('if file not exists copy file to target', function(cb) {
+          rimraf(out, function() {
+              ncp(src, out, {modified: true, clobber: false}, function (err) {
+                  assert.equal(fs.existsSync(out), true);
+                  cb();
+              });
+          });
+      });
+
+      it('change source file mtime and copy', function(cb) {
+          fs.utimesSync(src+"/a", new Date().getTime()/1000, new Date('2015-01-01 00:00:00').getTime()/1000);
+          ncp(src, out, {modified: true, clobber: false}, function (err) {
+              fs.stat(out+"/a", function(err, stats) {
+                  assert.equal(stats.mtime.getTime(), new Date('2015-01-01 00:00:00').getTime());
+                  cb();
+              });
+          });
+      });
+
+  });
+});