без каталога нельзя
var map = require('map-stream');
var fs = require('vinyl-fs');
var converter = require('sass-convert');
var log = function(file, cb) {
console.log(file.path);
cb(null, file);
};
fs.src(['./app/sass/**/*.sass'])
.pipe(map(log))
.pipe(converter({
from: 'sass',
to: 'scss',
}))
.pipe(fs.dest('./output'));