How it works…

The Cmd structure of the os/exec package provides the functions to access the output/input of the process. There are a few approaches to read the output of the process.

One of the simplest ways to read the process output is to use the Output or CombinedOutput method of the Cmd structure (gets Stderr and Stdout). While calling this function, the program synchronously waits till the child process terminates and then returns the output to a byte buffer.

Besides the Output and OutputCombined methods, the Cmd structure provides the Stdout property, where the io.Writer could be assigned. The assigned writer then serves as a destination for the process output. It could be a file, byte buffer or any type implementing the io.Writer interface.

The last approach to read the process output is to get the io.Reader from the Cmd structure by calling the StdoutPipe method. The StdoutPipe method creates the pipe between the Stdout, where the process writes the output, and provides Reader which works as the interface for the program to read the process output. This way the output of the process is piped to the retrieved io.Reader . 

Writing to a process stdin works the same way. Of all the options, the one with io.Writer will be demonstrated.

As could be seen, there are a few ways to read and write from the child process. The use of stderr and stdin is almost the same as described in steps 6-7. Finally, the approach of how to access the input/output could be divided this way:

• Synchronous (wait until the process ends and get the bytes): The Output and CombinedOutput methods of Cmd are used.
• IO: The output or input are provided in the form of io.Writer/Reader. The XXXPipe and StdXXX properties are the right ones for this approach.

The IO type is more flexible and could also be used asynchronously.