#+title: A simple shell script to get Australian weather forecast from BoM

#+date: <2022-01-13>

In this micropost I'll show how to write your own android weather app
("app" in a liberal sense) to retrieve weather for an Australian town,
using Melbourne as an example.

The short form (précis) 7-day forecasts, containing min / max
temperature, humidity level and chances of precipitation are available
as xml files [[http://www.bom.gov.au/catalogue/data-feeds.shtml][provided by the BoM]] - simply go there and get the link
for the state you are interested in.  For Victoria it is
<ftp://ftp.bom.gov.au/anon/gen/fwo/IDV10753.xml>.

So the first step is to download the xml to a temp directory, which
can be done with wget:

#+begin_src sh
cd $PREFIX/tmp
rm IDV10753.xml || true
wget ftp://ftp.bom.gov.au/anon/gen/fwo/IDV10753.xml
#+end_src

Next one needs to query the xml file for the relevant data.  Locate
the city name, date, temperatures and chance of pricipitation using
the nice [[https://en.wikipedia.org/wiki/XMLStarlet][xmlstarlet]] tool and format them nicely.

#+begin_src sh
result=`xml sel -t -m '//area[@description="Melbourne"]/forecast-period'\
 -v "substring-before(@start-time-local, 'T')" \
 -o " - min: " -v "element[@type='air_temperature_minimum']" \
 -o " - max: " -v "element[@type='air_temperature_maximum']" \
 -o " - " -v "text[@type='precis']" \
 -o " - chance of precipitation: " -v "text[@type='probability_of_precipitation']" \
 -n IDV10753.xml`
#+end_src

And finally, send the forecast to yourself using [[https://f-droid.org/en/packages/com.termux.api][Termux:API]].

#+begin_src sh
echo -e "7-day weather forecast in Melbourne:\n${result}" | \
    termux-sms-send -n 044444444 # replace 044444444 with your phone number
#+end_src

To use it in termux, it doesn't hurt to specify the location of the
shell in a shebang:

#+begin_src sh
#!/data/data/com.termux/files/usr/bin/bash
#+end_src

Finally, to make the script a bit more convenient to invoke, use
[[https://f-droid.org/en/packages/com.termux.widget/][Termux:Widget]], and copy the script to =~/.shortcut=, and you can make
it appear as a button in a desktop widget.

Enjoy the Melbourne weather!