Get lsof information about a file (list of processes that are accessing that file)

lsof.js

var exec = require('child_process').exec,
	util = require('util');

var target = process.argv[2];
if (!target) {
	return usage(1);
}

var FIELDS = ['pid', 'command', 'uid', 'lock'];
var FIELD_OPTIONS = {
	pid: { fn: Number },
	command : {},
	uid: { fn: Number },
	lock: {}
};

lsofFile(target, function (err, results) {
	if (err) {
		console.error(err);
	} else {
		console.log(results);
	}
});


function usage(exitCode) {
	console.log(util.format('Usage: %s %s <target>', process.argv[0], process.argv[1]));
	process.exit(exitCode >= 0 ? exitCode : 0);
}

function lsofFile(path, callback) {
	exec('/usr/bin/lsof -F pucl -f -- ' + target, function (err, stdout, stderr) {
		stderr = stderr ? stderr.toString() : '';
		if (stderr && stderr.indexOf("No such file or directory") >= 0) {
			err = new Error('File not found');
			err.code = 'ENOENT';
			err.errno = -2;
			return callback(err);
		}

		if (err && err.code !== 1) {
			return callback(new Error(stderr));
		}

		var results = [],
			entryIndex = 0,
			fieldIndex = 0;

		stdout.split('\n').forEach(function (line) {
			if (!line) {
				return;
			}
			
			var field = FIELDS[fieldIndex];
			var value = line.slice(1).trim();
			if (FIELD_OPTIONS[field].fn) {
				value = FIELD_OPTIONS[field].fn(value);
			}

			var entry = results[entryIndex] || (results[entryIndex] = {});
			entry[field] = value;
			
			fieldIndex++;
			if (fieldIndex >= FIELDS.length) {
				fieldIndex = 0;
				entryIndex++;
			}
		});

		return callback(null, results);
	});
}