Bash scripts for working with qr codes

decodeqr

#!/bin/bash

DECODEQR_TMPDIR=$(mktemp --tmpdir=$TMPDIR -d)
if [ $? -eq 0 -a ! -z "$DECODEQR_TMPDIR" ]; then
  #mkfifo $DECODEQR_TMPDIR/tmp.png
  gnome-screenshot -f $DECODEQR_TMPDIR/tmp.png
  zbarimg --quiet $DECODEQR_TMPDIR/tmp.png
  rm -rf $DECODEQR_TMPDIR
fi

encodeqr

#!/bin/bash

ENCODEQR_TEMPDIR=$(mktemp --tmpdir=$TMPDIR -d)
if [ $? -eq 0 -a ! -z $ENCODEQR_TEMPDIR ]; then
  if [ $# -eq 0 ]; then
    qrencode -o $ENCODEQR_TEMPDIR/tmpqrcode.png < /dev/stdin
  else
    qrencode -o $ENCODEQR_TEMPDIR/tmpqrcode.png "$*" < /dev/stdin
  fi
  eog -n $ENCODEQR_TEMPDIR/tmpqrcode.png
  rm -rf $ENCODEQR_TEMPDIR
fi

decodeqr decodes any qr codes currently displayed on the screen, writing the result(s) to stdout. If nothing is found, then nothing is written to stdout. This depends on gnome-screenshot and the zbar-tools packages on Ubuntu.

encodeqr generates a qr code and displays it, temporarily. The content of the qr code can be specified either via command line arguments or via stdin; see the documentation for qrencode for more info. This depends on the qrencode and eog packages on Ubuntu.

For security reasons, ideally TMPDIR would be on a memory-only filesystem such as tmpfs. Note that at least on linux, if the TMPDIR environment variable is empty then mktemp will default to creating a temporary directory inside /tmp.

One could avoid writing the screen captures or temporary images to a file by using a fifo, not sure why uncommenting the mkfifo line (and starting gnome-screenshot in the background using &) doesn't work. Assuming you could find a way to get gnome-screenshot and zbarimg to agree on the file type, one could avoid named fifo's altogether via pipe(2) and /dev/fd, but I'm not sure how to accomplish that with my limited bash scripting skills.