Add option to cp to only copy contents of directory (#788)

* Add option to not copy source directory

* Cleanup

* Update condition to be consistent

__tests__/io.test.ts

@@ -90,6 +90,29 @@ describe('cp', () => {
     )
   })
 
+  it('copies directory into existing destination with -r without copying source directory', async () => {
+    const root: string = path.join(
+      getTestTemp(),
+      'cp_with_-r_existing_dest_no_source_dir'
+    )
+    const sourceFolder: string = path.join(root, 'cp_source')
+    const sourceFile: string = path.join(sourceFolder, 'cp_source_file')
+
+    const targetFolder: string = path.join(root, 'cp_target')
+    const targetFile: string = path.join(targetFolder, 'cp_source_file')
+    await io.mkdirP(sourceFolder)
+    await fs.writeFile(sourceFile, 'test file content', {encoding: 'utf8'})
+    await io.mkdirP(targetFolder)
+    await io.cp(sourceFolder, targetFolder, {
+      recursive: true,
+      copySourceDirectory: false
+    })
+
+    expect(await fs.readFile(targetFile, {encoding: 'utf8'})).toBe(
+      'test file content'
+    )
+  })
+
   it('copies directory into non-existing destination with -r', async () => {
     const root: string = path.join(getTestTemp(), 'cp_with_-r_nonexistent_dest')
     const sourceFolder: string = path.join(root, 'cp_source')