Start a quick Javascript repl with underscore preloaded using nodejs. Requires nodejs and npm-installed underscore.

underscore-shell.js

var fs = require('fs');
var repl = require('repl');

var __ = require('underscore')._;

var files = {};
var jsonFiles = process.argv.slice(2);
jsonFiles.forEach(function(val) {
    files[val] = JSON.parse(fs.readFileSync(val));
});

var shell = repl.start({
    prompt: "underscore> ",
    input: process.stdin,
    output: process.stdout
});

shell.context.files = files;
shell.context.__ = __; // in Nodejs's repl, _ is a placeholder for "last result," so we need to use __ instead.