Log grunt output into file. Intercepts grunt.log.write to do its job.

grunt-log-to-file.js

function gruntLogToFile(grunt, logFilePath) {
    logFilePath = logFilePath || grunt.option('log-file');
    if (!logFilePath) {
        throw new Error('No log file path specified');
        return null;
    }

    var namespace = '_gruntLogToFile_' + logFilePath;
    var origLogFunc = grunt.log.write;

    // Check if stream/hook has already been created
    while(origLogFunc && !origLogFunc[namespace]) {
        origLogFunc = grunt.util.hooker.orig(grunt.log, 'write');
    }
    if (origLogFunc && origLogFunc[namespace]) {
        // Return stream if it has already been created
        return origLogFunc[namespace];
    }

    var logFileStream = fs.createWriteStream(logFilePath, {flags: 'a'});
    if (logFileStream.writable) {
        grunt.util.hooker.hook(grunt.log, 'write', function writeAndLog() {
            if (logFileStream.writable) {
                logFileStream.write(arguments[0].stripColors);
            }
        });
        grunt.util.hooker.hook(grunt.util, 'exit', function drainLogBefExit(exitCode) {
            if (logFileStream._queue.length) {
                logFileStream.once('drain', function () {
                    grunt.util.exit(exitCode);
                })
                return grunt.util.hooker.preempt();
            }
        });
        grunt.log.write[namespace] = logFileStream;
    }
    return logFileStream;
}