Due to a rather embarrassing episode in #archlinux a couple of weeks ago, where I naively shared one of the first bash scripts I had written without first looking back over it¹, and had to subsequently endure what felt like the ritual code mocking, but was in fact some helpful pointers as to how I could make the script suck less (a lot less) I have been going through those older scripts and applying the little knowledge that I have picked up in the interim; reappraising the usefulness of the scripts as I go.

One that has proved to be of some utility for many years now is a simple wrapper script I wrote to help manage my finances. Like many useful scripts, it was written quickly and has been in constant use ever since; becoming almost transparent it is so ingrained in my workflow.

The script allows me to manage the lag between when a company emails me an invoice and when the payment is actually due. I find that companies will typically email their invoices to me some weeks in advance, whereupon I will make a mental note and then, unsurprisingly, promptly forget all about it, thereby opening myself up for penalties for late payment. It didn’t take me long (well, in my defence, a lot less time than it took for invoices to become digital) to realise that there was a better way™ - a script.

The at command is purpose built for running aperiodic commands at a later time (whereas cron is for periodic tasks). So, using at(1), once I receive an invoice, I can set a reminder closer to the final payment window, thereby avoiding both the late payment penalty—and the loss of interest were I to pay it on receipt. I just needed a script to make it painless to achieve.

The main function of the script is pretty self-explanatory:

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aread() {
  read -p "Time of message? [HH:MM] " attime
  read -p "Date of message? [DD.MM.YY] " atdate
  read -p "Message body? " message

  timexp='^[0-9]{2}:[0-9]{2}'
  datexp='^[0-9]{2}.[0-9]{2}.[0-9]{2}'

  if [[ $attime =~ $timexp && $atdate =~ $datexp ]]; then
     at "$attime" "$atdate" << EOF
     printf '%s\n' "$message" | mutt -s "REMINDER" jasonwryan@gmail.com
EOF
  else
     printf '%s\n' "Incorrectly formatted values, bailing..." && exit 1
  fi
}

Now, an invoice arrives, I open it and fire up a scratchpad, and follow the prompts. A couple of weeks later, the reminder email arrives and I login to my bank account and dispatch payment. You could, of course, have the script trigger some other form of notification, but an email works well for me.

The rest of the script is similarly basic; just some options for listing and reading any queued jobs and some more rudimentary checking. The full script is in my bitbucket repo².

Update 7/09/14

Not more than a couple of hours after posting this, Florian Pritz pinged me in #archlinux with some great suggestions for improving the script. I particularly liked relying on date(1) handling the input format for the time and date values. He also suggested a readline wrapper called (appropriately enough) rlwrap and a tmpfile to better manage input validation. You can see his full diff of changes. In the end, I adopted the date suggestion but passed on rlwrap. Thanks for the great pointers, Florian.

Notes

1. In the interests of full disclosure, the most egregious line was myterm=$(echo $TERM) which I would hope I copied blindly from somewhere else, but accept full responsibility for nonetheless.
2. Don’t poke around too much in there, I still have quite a lot of cleaning up to do…

Creative Commons image by Adelle and Justin on Flickr.