prefixedio (Golang package: prefixedio) is a package for Go
that takes an io.Reader and de-multiplexes line-oriented data based
on a line prefix to a set of readers.
Install using go get github.com/mitchellh/prefixedio.
Full documentation is available at http://godoc.org/github.com/mitchellh/prefixedio
Below is an example of its usage ignoring errors:
// Assume r is some set io.Reader. Perhaps a file, network, anything.
var r io.Reader
// Initialize the prefixed reader
pr, _ := prefixedio.NewReader(r)
// Grab readers for a couple prefixes
errR, _ := pr.Prefix("err: ")
outR, _ := pr.Prefix("out: ")
// Copy the data to different places based on the prefix
go io.Copy(os.Stderr, errR)
go io.Copy(os.Stdout, outR)