Last Updated: February 25, 2016
· ryepdx

Display an image from stdout [ubuntu]

To send bitcoin from my mobile phone to a plaintext address on my laptop, I like to use QR codes. At first I used websites like qrstuff.com to generate the QR codes, but leaving the command line just to generate and display an image felt like too much of a hassle to me. Then I started using the feh and qrencode utilities in Ubuntu's package repositories, but that involved creating an image file on my hard drive and then deleting it afterward, which felt messy. So I found a quick and easy way to generate and display a QR code from the command line without creating an intermediate file.

The setup:

sudo apt-get install qrencode
sudo apt-get install giblib-dev libimlib2 libcurl4-openssl-dev libpng-dev libX11-dev libXinerama-dev
git clone https://github.com/derf/feh.git
cd feh
sudo make install

And to use the new qrencode and feh combo to, for example, display the QR code for Andreas Antonopoulos' Dorian Nakamoto assistance fund:

qrencode 1Dorian4RoXcnBv9hnQ4Y2C1an6NJ4UrjX -o - | feh -

Note that though there is a copy of feh already in the Ubuntu package repositories, it's an older version that does not support reading images from stdin. Thus it is necessary to compile our own copy from the git repository.

In the example above, the -o option on qrencode specifies where the generated image should be output, and passing - to that option specifies that it should be sent to stdout. Likewise, the - passed to feh specifies that feh should read the image from stdin.

Finally, because I am extraordinarily lazy, I created a function in my ~/.bashrc file to save my future self a few extra keystrokes:

function qrcode () {
    qrencode $@ -o - | feh -;

Which turns the previous example into the slightly more succinct:

qrcode 1Dorian4RoXcnBv9hnQ4Y2C1an6NJ4UrjX
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