Change other file inside EventStream of other gulp - gulp

Question

I have one interesting question. Is it possible to change some file inside open stream (EventStream) inside gulp?
I have that stuff. I want to read some file inside opened stream and write that stuff to other file. How I can do it? Thanks.
gulp.task('handleGlobalStorage', function () {
return gulp.src('./global_storage.js')
.pipe(setEnvHostAndProxy())
.pipe(gulp.dest('./built'));
});
function setEnvHostAndProxy() {
return es.map(function(file, cb) {
var fileContent = file.contents.toString();
//some changes inside content
// if (!gutil.env.dev) return;
/* I have stuff that fetched from file and I modify it that I send it
down to pipe. But also I want to insert this stuff inside other
file. How I can do it? Should I create WritableStream of that file
and merge it ?*/
file.contents = new Buffer(fileContent);
// send the updated file down the pipe
cb(null, file);
});
}

Answer 1

I resolved that issue, here is solution (I will not show all code, only general). The main concept is - open file and write new stuff inside pipe :) that's all.
function setEnvHostAndProxy() {
var bsConfigFileContent = fs.readFileSync('./bs-config.js', 'utf8'),
bsConfigProxyPattern = /(proxyUrl\s?=\s?)["|'](.*)["|']/;
return es.map(function (file, cb) {
var fileContent = file.contents.toString(),
prodHost = fileContent.match(generateRegExpForHosts('prodHost'))[1],
prodProxy = fileContent.match(generateRegExpForHosts('prodProxy'))[1],
devProxy = fileContent.match(generateRegExpForHosts('devProxy'))[1],
devHost = fileContent.match(generateRegExpForHosts('devHost'))[1],
changedBsConfigFileStream,
res;
if (!gutil.env.dev) {
res = prodHandler();
changedBsConfigFileStream = bsConfigHandler(prodHost);
} else {
res = devHandler();
changedBsConfigFileStream = bsConfigHandler(devProxy);
}
fs.writeFile('./bs-config.js', changedBsConfigFileStream, 'utf8', function (err) {
if (err) throw (err);
});
file.contents = new Buffer(res);
cb(null, file);
} });