Log command's stderr output

main.go

@@ -47,7 +47,7 @@ func validateArgs(args []string) {
 		dieUsage(fmt.Sprintf("Invalid version specified: %v  Supported version: %v", *protocolVersionFlag, ProtocolVersion))
 	}
 
-	logger.Printf("Flag values:\n  dir: %v\n  log: %v\n  protocol_version: %v\n  Args: %v\n", *cdFlag, *logFlag, *protocolVersionFlag, args)
+	logger.Printf("dir:%v, log:%v, protocol_version:%v, args:%v\n", *cdFlag, *logFlag, *protocolVersionFlag, args)
 }
 
 func notFifo(path string) bool {

process.go

@@ -13,14 +13,16 @@ func startCommandPipeline(proc *exec.Cmd, input <-chan Packet, inputDemand chan<
 	cmdOutput, err := proc.StdoutPipe()
 	fatalIf(err)
 
-	// cmdError, err := proc.StderrPipe()
-	// fatalIf(err)
+	cmdError, err := proc.StderrPipe()
+	fatalIf(err)
 
 	execErr := proc.Start()
 	fatalIf(execErr)
 
 	go writeToCommandStdin(cmdInput, input, inputDemand)
 
+	go printStderr(cmdError)
+
 	output := make(chan Packet)
 	go readCommandStdout(cmdOutput, outputDemand, output)
 
@@ -94,3 +96,22 @@ func readCommandStdout(cmdOutput io.ReadCloser, outputDemand <-chan Packet, outp
 		}
 	}
 }
+
+func printStderr(cmdError io.ReadCloser) {
+	var buf [BufferSize]byte
+
+	defer func() {
+		cmdError.Close()
+	}()
+
+	for {
+		bytesRead, readErr := cmdError.Read(buf[:])
+		if bytesRead > 0 {
+			logger.Printf(string(buf[:bytesRead]))
+		} else if readErr == io.EOF || bytesRead == 0 {
+			return
+		} else {
+			fatal(readErr)
+		}
+	}
+}