line_count.js

#!/usr/bin/env node
var argv = require('optimist')
    .usage('Count the lines in a file.\nUsage: $0')
    .demand('f')
    .alias('f', 'file')
    .describe('f', 'Load a file')
    .argv
;

var fs = require('fs');
var s = fs.createReadStream(argv.file);

var lines = 0;
s.on('data', function (buf) {
    lines += buf.toString().match(/\n/g).length;
});

s.on('end', function () {
    console.log(lines);
});