Grunt imagemin - watch multiple files/folders optimise single file?

Question

Is it possible to watch multiple files/folders but optimise only a single file using grunt-contrib-imagemine and grunt-contrib-watch?

I tried like this: (part of gruntfile)

imagemin: {
  dist: {
    cwd: 'images/modules',
    files: ['images/modules/**/*.{png,jpg,gif}'],
    dest: 'images/modules'
  }
},

watch: {
   images: {
      files: ['images/modules/**/*.{png,jpg,gif}'],
      tasks: ['imagemin'],
      options: {
      spawn: false,
      }
    }
}

grunt.event.on('watch', function(action, filepath, target) {
  if (grunt.file.isMatch(grunt.config('watch.images.files'), filepath)) {
      grunt.config('imagemin.dist.src', [filepath]);
   }
});

But it doesn't work. It returns:

Running "imagemin:dist" (imagemin) task
Verifying property imagemin.dist exists in config...OK
Files: [no src] -> images/modules
Options: optimizationLevel=7, progressive, pngquant=false
Options: optimizationLevel=7, progressive, pngquant=false
Warning: path must be a string

Any ideas? Thank you.

Answer 1

Based on the grunt-contrib-imagemin docs the file attribute takes an object of src/dest (key/value) pairs.

files: {                         // Dictionary of files
    'dist/img.png': 'src/img.png', // 'destination': 'source'
    'dist/img.jpg': 'src/img.jpg',
    'dist/img.gif': 'src/img.gif'
  }

I believe that is why you are getting the error.

To do what you want, at least what i think you want i would add another subtask to imagemin like below.

imagemin: {
  dist: {
    files: [{
    expand: true,                              // Enable dynamic expansion
    cwd: 'images/modules',                     // Src matches are relative to this path
    src: ['images/modules/**/*.{png,jpg,gif}'],// Actual patterns to match
    dest:'images/modules'                      // Destination path prefix
    }]
  },
  single: {
    cwd: 'images/modules',
    files: 'images/modules/img.png': 'images/modules/img.png', 
    dest: 'images/modules'
  }

},
watch: {
    images: {
      files: ['images/modules/**/*.{png,jpg,gif}'],
      tasks: ['imagemin:single'],
      options: {
      spawn: false,
      }
    }
}

so the above watch command will watch all files that match the files regex and will carry out the single subtask of the watch main task.

Again i think this is what you want to do but if not could you explain it more?