gulp-php.js

var through = require("through2");
var exec    = require("child_process").exec;

// through2 docs: https://github.com/rvagg/through2

module.exports = function (options) {
  
  // Not necessary to accept options but nice in case you add them later
  options = options || {};
  
  // through2.obj(fn) is a convenience wrapper around through2({ objectMode: true }, fn)
  return through.obj(function (file, enc, cb) {
    
    // Always error if file is a stream since gulp doesn't support a stream of streams
    if (file.isStream()) {
      this.emit('error', new Error('Streaming not supported in gulp-php lib'));
      return cb();
    }
  
    // Handle the file, process it somehow
    exec("php " + file.path, function (error, stdout, stderr) {
      
      // If there's an error, this stops gulp but it's not great, needs work
      if (error) {
        this.emit('error', error);
        return cb(error);
      }
      
      // Change the contents of the file, if necessary (must be a Buffer)
      file.contents = new Buffer(stdout, "utf8");
      
      // Push the file back onto the stream queue (this was this.queue in through lib)
      this.push(file);
  
      // Call the passed cb so the stream continues on
      cb();
    
    // Bind here or else save off var that = this earlier
    }.bind(this));

  });

};

Original comment from the author: If you don't need to modify the file, obviously you can make it even simpler by doing whatever you want with file.contents, then just this.push(file) and cb() when you're done.