gunrt-contrib-copy renaming file extensions

i have a directory and a number of sub directories so when i look for my files i use a globbing pattern like

'src/**/*.js'

the trouble is i want to rename extension to .old.js

the snag is i need the .old.js file to be renamed and stay in the directory it was found but it is not clear to me how this is achieved.

I have tried a variety of things and so far the only thing that has worked is to look at each directory seperately in a seperate copy task which is not really what i want to do.

Anyone have any other approach?

Initial directory structure

Consider the following fictitious directory structure:

src
├── 1.js
├── 2.js
└── a
    ├── 3.js
    ├── 4.js
    └── b
        ├── 5.js
        ├── 6.js
        └── c
            ├── 7.js
            └── 8.js

---

Example One

Gruntfile.js

You can configure your grunt-contrib-copy Task as follows:

module.exports = function(grunt) {

    grunt.initConfig({

        copy: {
            js: {
                files: [{
                    expand: true,
                    dot: true,
                    cwd: 'src',
                    dest: 'src/',
                    src: [
                        '**/*.js'
                    ],
                    rename: function(dest, src) {
                        return dest + src.replace('.js', '.old.js');
                    }
                }]
            }
        }

    });

    grunt.loadNpmTasks('grunt-contrib-copy');

    grunt.registerTask('default', [
        'copy:js'
    ]);

};

Resultant directory structure (Example One)

After running $ grunt via the CLI using the Gruntfile.js configured as shown above will result in the following:

(Note: each original .js file has been duplicated to the same folder location and the .old.js extension added):

src
├── 1.js
├── 1.old.js
├── 2.js
├── 2.old.js
└── a
    ├── 3.js
    ├── 3.old.js
    ├── 4.js
    ├── 4.old.js
    └── b
        ├── 5.js
        ├── 5.old.js
        ├── 6.js
        ├── 6.old.js
        └── c
            ├── 7.js
            ├── 7.old.js
            ├── 8.js
            └── 8.old.js

---

Example 2

If you don't want to keep the original .js file then you'll also need to use grunt-contrib-clean to delete the originals.

Gruntfile.js

module.exports = function(grunt) {

    grunt.initConfig({

        copy: {
            js: {
                files: [{
                    expand: true,
                    dot: true,
                    cwd: 'src',
                    dest: 'src/',
                    src: [
                        '**/*.js'
                    ],
                    rename: function(dest, src) {
                        return dest + src.replace('.js', '.old.js');
                    }
                }]
            }
        },

        clean: {
            originaljs: [
                'src/**/*.js',
                '!src/**/*.old.js'
            ]
        }

    });

    grunt.loadNpmTasks('grunt-contrib-copy');
    grunt.loadNpmTasks('grunt-contrib-clean');

    grunt.registerTask('default', [
        'copy:js',
        'clean:originaljs'
    ]);

};

Resultant directory structure (Example Two)

This time after running $ grunt using the revised Gruntfile.js will result in the following:

(Note: each original .js has been deleted and only the .old.js extension exist.)

src
├── 1.old.js
├── 2.old.js
└── a
    ├── 3.old.js
    ├── 4.old.js
    └── b
        ├── 5.old.js
        ├── 6.old.js
        └── c
            ├── 7.old.js
            └── 8.old.js