Add input file and os.Stdin support

[pantsing]

now it can be used as $cat name card.vcf | qrcode -o name card.png

[skip2]

I suggest prioritising the -i flag, then command line arguments, then reading from STDIN last, like:

content := ""
argsContent := strings.Join(flag.Args(), " ")

if *inFile != "" {
	b, err := ioutil.ReadFile(*inFile)
	if err != nil {
		checkError(err)
	}
	content = string(b)
} else if argsContent != "" {
	content = argsContent
} else {
	b, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		checkError(err)
	}
	content = string(b)
}

[skip2]

Hey,

I think reading content from STDIN/a file is a nice addition :)

After this pull request there are three ways to specify content:

• String from input file:

$ qrcode -i input_filename | display

• String on command line:

$ qrcode hello | display

• String on STDIN:

$ echo -n hello | qrcode | display

• No arguments: (same as string on STDIN, only you type into the terminal and then press Ctrl+D)

$ qrcode | display

If you try the "qrcode hello | display" method, it now hangs and waits for something on STDIN.

I suggest taking content from one source only (first the -i flag, then command line arguments, or lastly STDIN), so the usage is more obvious and easier to explain. This would work well.

thanks,

Tom

[pantsing]

Thanks Tom, you are right.