add filter option, fixes sindresorhus#63

index.d.ts

@@ -46,6 +46,22 @@ declare namespace cpy {
 		@default true
 		*/
 		readonly ignoreJunk?: boolean;
+
+		/**
+		Function to filter copied files. Return true to include, false to exclude. Can also return a Promise that resolves to true or false.
+
+		@example
+		```
+		import cpy = require('cpy');
+
+		(async () => {
+			await cpy('foo', 'destination', {
+				filter: name => !name.includes('NOCOPY')
+			});
+		})();
+		```
+		*/
+		readonly filter?: (basename: string) => (boolean | Promise<boolean>);
 	}
 
 	interface ProgressData {

index.js

@@ -8,6 +8,7 @@ const globby = require('globby');
 const hasGlob = require('has-glob');
 const cpFile = require('cp-file');
 const junk = require('junk');
+const pFilter = require('p-filter');
 const CpyError = require('./cpy-error');
 
 const defaultOptions = {
@@ -74,6 +75,20 @@ module.exports = (source, destination, {
 			throw new CpyError(`Cannot copy \`${source}\`: the file doesn't exist`);
 		}
 
+		if (options.filter !== undefined) {
+			const filteredFiles = await pFilter(files, options.filter, {concurrency: 1024});
+			files = filteredFiles;
+		}
+
+		if (files.length === 0) {
+			progressEmitter.emit('progress', {
+				totalFiles: 0,
+				percent: 1,
+				completedFiles: 0,
+				completedSize: 0
+			});
+		}
+
 		const fileProgressHandler = event => {
 			const fileStatus = copyStatus.get(event.src) || {written: 0, percent: 0};
 

index.test-d.ts

@@ -27,6 +27,12 @@ expectType<Promise<string[]> & ProgressEmitter>(
 	cpy('foo.js', 'destination', {concurrency: 2})
 );
 
+expectType<Promise<string[]> & ProgressEmitter>(
+	cpy('foo.js', 'destination', {filter: () => true})
+);
+expectType<Promise<string[]> & ProgressEmitter>(
+	cpy('foo.js', 'destination', {filter: async () => true})
+);
 
 expectType<Promise<string[]>>(
 	cpy('foo.js', 'destination').on('progress', progress => {

package.json

@@ -49,7 +49,8 @@
 		"has-glob": "^1.0.0",
 		"junk": "^3.1.0",
 		"nested-error-stacks": "^2.1.0",
-		"p-all": "^2.1.0"
+		"p-all": "^2.1.0",
+		"p-filter": "^2.1.0"
 	},
 	"devDependencies": {
 		"ava": "^2.1.0",

readme.md

@@ -106,6 +106,21 @@ Default: `true`
 
 Ignores [junk](https://github.com/sindresorhus/junk) files.
 
+#### filter
+
+Type: `string | Function`
+
+Function to filter copied files. Return true to include, false to exclude. Can also return a Promise that resolves to true or false.
+
+```js
+const cpy = require('cpy');
+
+(async () => {
+	await cpy('foo.js', 'destination', {
+		filter: name => !name.includes('NOCOPY')
+	});
+})();
+```
 ## Progress reporting
 
 ### cpy.on('progress', handler)

test.js

@@ -54,6 +54,20 @@ test('throws on invalid concurrency value', async t => {
 	await t.throwsAsync(cpy(['license', 'package.json'], t.context.tmp, {concurrency: 'foo'}));
 });
 
+test('copy array of files with filter', async t => {
+	await cpy(['license', 'package.json'], t.context.tmp, {filter: name => name !== 'license'});
+
+	t.false(fs.existsSync(path.join(t.context.tmp, 'license')));
+	t.is(read('package.json'), read(t.context.tmp, 'package.json'));
+});
+
+test('copy array of files with async filter', async t => {
+	await cpy(['license', 'package.json'], t.context.tmp, {filter: async name => name !== 'license'});
+
+	t.false(fs.existsSync(path.join(t.context.tmp, 'license')));
+	t.is(read('package.json'), read(t.context.tmp, 'package.json'));
+});
+
 test('cwd', async t => {
 	fs.mkdirSync(t.context.tmp);
 	fs.mkdirSync(path.join(t.context.tmp, 'cwd'));