read_from_stdin.md

Read From STDIN

Go is good for small command line utilities. In my process to learn Go I wanted to write some small command line utilities so I thought about what command line utilities I was missing...

I used to work with DNS so I decided that the process of opening a browser to find a punycode converter and convert a string to or from punycode, should be done on the command line. I had some Perl utilities, so I decided to port these to Go.

I found this snippet on Yourbasic.org/golang

scanner := bufio.NewScanner(os.Stdin)
for scanner.Scan() {
    fmt.Println(scanner.Text())
}

if err := scanner.Err(); err != nil {
    log.Println(err)
}

I implemented some utilities (punydecode and punyencode), but after some afterthought I boiled the two into one: punycode, since punycode is easy to identify due to the prefix: xn--, so you could do with a single utility.

Since I wanted my utility to both support a string argument and STDIN, I made the following construct:

    argsWithoutProg := os.Args[1:]

    var argString string

    if len(argsWithoutProg) <= 0 {
        scanner := bufio.NewScanner(os.Stdin)

        for scanner.Scan() {
            argString = scanner.Text()
        }

        if err := scanner.Err(); err != nil {
            log.Println(err)
            return 2
        }
    } else {
        argString = os.Args[1] // we only take a single parameter, the string to process
    }

An issue I have not been able to address it how you test reading from STDIN in a Go test suite, I could use Bats or similar, but that would not integrate as well as expected.

Resources and References

1. Yourbasic.org/golang: Read a file (stdin) line by line
2. Go standard library: os - Variables
3. GitHub: punydecode
4. GitHub: punyencode
5. GitHub: punycode
6. Bats