Alternatives for clang

October 21st, 2016 No comments

In Ubuntu, installing clang-3.6 doesn’t provide you with clang or clang++ links to the clang-3.6 or clang++-3.6 executables, or a way of easily selecting the active clang version when you have multiple versions installed.

This command/script creates a clang group using update-alternatives so you can easily execute clang (without the version number) and switch between different clang versions.

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Import Tellico books into Calibre

April 23rd, 2016 No comments

I used to maintain my dead-tree book collection in Alexandria. When that stopped being developed I switched to Tellico. Tellico however doesn’t have a simple way of retrieving cover images, so recently I switched to using Calibre.

The following python script automates the process of converting from Tellico to Calibre so you don’t have to re-enter all the books by hand.

Install requirements (BeautifulSoup v4 is used to parse the XML):

sudo apt-get install python-bs4

Extract the Tellico data (the Tellico file (*.tc) is just a zip file with the XML data and cover images):

mkdir /tmp/tellico
cd /tmp/tellico
unzip [/path/to/tellico/file/]

Now run the import/conversion script. The only argument it needs is the path to the tellico.xml file that you just unzipped:

python tellico.xml

All the books are tagged with “Print”, and if they’re marked as loaned out in Tellico they also get the “Loaned” tag. The following data is imported:

  • Title
  • Authors
  • ISBN
  • Cover image
  • Publisher
  • Published date
  • Comments
  • Rating

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Monitoring files with vim

November 17th, 2015 No comments

It turns out that monitoring a file with vim is harder than it should be. Scripts such as Tail-Bundle and WatchForChanges rely on vim’s CursorHold events which only trigger once. Unlike tail -f, they only work if you’re active in that vim session and pressing keys to cause CursorHold to re-arm.

tail -f works well, but lacks the syntax highlighting and other features from vim.

Some other options require 2 terminals, or 2 separate scripts.

The solution below is very similar to tail -f. The primary difference is that it only monitors a single file at a time.

Get the latest version from:


# Usage: <filename>
# This script turns vim into a `tail -f` equivalent, but with syntax
# highlighting and all the other goodies.
# A version of vim compiled with +clientserver is required.
# On Ubuntu 14.04, vim.tiny, vim.basic and vim.nox won't work.
# vim.gtk is compiled with +clientserver, so `apt-get install vim-gtk`
# Author: Gabriel Burca <gburca dash github at ebixio dot com>

# Pick one of: vim|view|gvim|gview, etc...

# A unique name for the server, in case we monitor multiple files.

doForever() {
    # Give the vim server a chance to start
    sleep 2

    # Move to the end of the file
    $VI --servername $NAME --remote-send '<C-\><C-N>:edit!<CR>G' > /dev/null 2>&1 || exit

    while true; do
        # This blocks until the file changes, or the timeout expires
        inotifywait --quiet --quiet --timeout 10 --event modify "$1"
        # 0 = the file was modified
        # 2 = the timeout expired
        if (( $? == 0 || $? == 2 )); then
            $VI --servername $NAME --remote-send '<C-\><C-N>:edit!<CR>G' > /dev/null 2>&1 || exit
            exit 1

        # It's possible for the file to be modified before we loop back to
        # `inotifywait`, but we'll pick it up on the next round.

# Kick off the vim client script in the background
coproc doForever "$1"

# Now start the server
$VI --servername $NAME --remote-silent "$1"
# Nothing below here executes until the `tail` server exits.

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DigiKam 4.10 on Ubuntu 14.04

May 30th, 2015 No comments

These are the steps I found are required to install DigiKam v4.10 on Ubuntu. In my case I ran into problems with libavcodec (ffmpeg/libav) and issues stemming from the ffmpeg project fork. YMMV.

First install digikam:

add-apt-repository ppa:philip5/extra
apt-get update
apt-get install digikam

At this point everything should have worked nicely. Unfortunately digikam (version: 4:4.10.0-trusty~ppa3) wouldn’t start up. Running it from the command line showed that I was missing To confirm:

ldd /usr/bin/digikam | grep libavcodec

The normal solution to this would have been:

apt-get install libavcodec-extra-53

But life is not that simple. Ubuntu deprecated and removed libavcodec-extra-53 and claims libav-tools should be used instead. libav-tools however doesn’t include a file, so after a bit of hunting around, I decided to just build it from source. Here are the steps:

git clone git://
cd ffmpeg
git checkout -b ver53 dd453f
./configure --prefix=/usr/local --disable-ffmpeg --disable-ffplay --disable-ffprobe --disable-ffserver --disable-avdevice --disable-swresample --disable-swscale --disable-postproc --disable-avfilter --enable-shared --disable-debug --enable-gpl --enable-x11grab
sudo su -

After this, digikam started up properly.


gitk --all libavcodec/version.h shows that after the dd453f commit the libavcodec version changes to 54, so that’s why that commit was used.

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Temperature sensor: TMP36, DHT22, and 10K Thermistor

January 30th, 2014 No comments

Here’s a quick comparison of 3 different “low cost” temperature sensors:

This is how accurate they each claim to be:

Model Accuracy in °C Accuracy in °F
TMP36 ±2.00°C ±3.6°F
Thermistor ±0.45°C ±0.8°F
DHT22 ±0.50°C ±0.9°F

All the data below was collected with a BeagleBone Black which has a 12-bit ADC. The 10K thermistor was hooked up in a voltage divider configuration with a 1% 10K resistor. The DHT22 uses a thermistor inside as well, but has a digital output. Readings were taken every 3s over a 2 hour period.

The sensors are all positioned within 1/4″ of each other. The slow temperature drifts are from the house cooling and the furnace heating it back up.



I used a running average filter with a window of 10 samples to clean up the noise a bit and these are the results.

Temperature - 30s running average

Temperature – 30s running average

Finally, taking the 10K thermistor as ground truth, these are the differences observed. The TMP36 is consistently about 2°F lower than the thermistor, and the DHT22 is roughly 1°F higher even though it’s also using a thermistor inside. I don’t know how accurate the ADC inside the DHT22 is, so that might explain some of the difference.

Deltas between different temperature sensors.

Deltas between different temperature sensors.

In conclusion, when you hear someone say “I keep my thermostat at 67°F” and another guy responds “My wife would kill me if I did that. I keep mine at 73°F” they might both be keeping their temperature at 70°F. It just depends on what temperature sensor their thermostat is using, and how well it was calibrated.

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