24 Oct, 2019

Hacky scripts

The most fun way to learn to code

As a CS student, I see a lot of people around me doing courses online to learn to code. Don’t get me wrong—it probably works for some. Everyone learns differently. But that’s only going to get you so far. Great you know the syntax, you can solve some competitive programming problems, but that’s not quite enough, is it? The actual learning comes from applying it in solving actual problems—not made up ones. (inb4 some seething CP bro comes at me)

Now, what’s an actual problem? Some might define it as real world problems that people out there face, and solving it probably requires building a product. This is what you see in hackathons, generally.

If you ask me, however, I like to define it as problems that you yourself face. This could be anything. Heck, it might not even be a “problem”. It could just be an itch that you want to scratch. And this is where hacky scripts come in. Unclear? Let me illustrate with a few examples.

Now playing status in my bar

If you weren’t aware already—I rice my desktop. A lot. And a part of this cohesive experience I try to create involves a status bar up at the top of my screen, showing the time, date, volume and battery statuses etc.

So here’s the “problem”. I wanted to have my currently playing song (Spotify), show up on my bar. How did I approach this? A few ideas popped up in my head:

Send playerctl’s STDOUT into my bar
Write a Python script to query Spotify’s API
Write a Python/shell script to query Last.fm’s API

The first approach bombed instantly. playerctl didn’t recognize my Spotify client and whined about some dbus issues to top it off. I spent a while in that rabbit hole but eventually gave up.

My next avenue was the Spotify Web API. One look at the docs and I realize that I’ll have to make more than one request to fetch the artist and track details. Nope, I need this to work fast.

Last resort—Last.fm’s API. Spolier alert, this worked. Also, arguably the best choice, since it shows the track status regardless of where the music is being played. Here’s the script in its entirety:

#!/usr/bin/env bash
# now playing
# requires the last.fm API key

source ~/.lastfm    # `export API_KEY="<key>"`
fg="$(xres color15)"
light="$(xres color8)"

USER="icyphox"
URL="http://ws.audioscrobbler.com/2.0/?method=user.getrecenttracks"
URL+="&user=$USER&api_key=$API_KEY&format=json&limit=1&nowplaying=true"
NOTPLAYING=" "    # I like to have it show nothing
RES=$(curl -s $URL)
NOWPLAYING=$(jq '.recenttracks.track[0]."@attr".nowplaying' <<< "$RES" | tr -d '"')


if [[ "$NOWPLAYING" = "true" ]]
then
	TRACK=$(jq '.recenttracks.track[0].name' <<< "$RES" | tr -d '"')
	ARTIST=$(jq '.recenttracks.track[0].artist."#text"' <<< "$RES" | tr -d '"')
	echo -ne "%{F$light}$TRACK %{F$fg}by $ARTIST"
else
	echo -ne "$NOTPLAYING"
fi

The source command is used to fetch the API key which I store at ~/.lastfm. The fg and light variables can be ignored, they’re only for coloring output on my bar. The rest is fairly trivial and just involves JSON parsing with jq. That’s it! It’s so small, but I learnt a ton. For those curious, here’s what it looks like running:

Update latest post on the index page

This pertains to this very blog that you’re reading. I wanted a quick way to update the “latest post” section in the home page and the blog listing, with a link to the latest post. This would require editing the Markdown source of both pages.

This was a very interesting challenge to me, primarily because it requires in-place editing of the file, not just appending. Sure, I could’ve come up with some sed one-liner, but that didn’t seem very fun. Also I hate regexes. Did a lot of research (read: Googling) on in-place editing of files in Python, sorting lists of files by modification time etc. and this is what I ended up on, ultimately:

#!/usr/bin/env python3

from markdown2 import markdown_path
import os
import fileinput
import sys

# change our cwd
os.chdir("bin")

blog = "../pages/blog/"

# get the most recently created file
def getrecent(path):
    files = [path + f for f in os.listdir(blog) if f not in ["_index.md", "feed.xml"]]
    files.sort(key=os.path.getmtime, reverse=True)
    return files[0]

# adding an entry to the markdown table
def update_index(s):
    path = "../pages/_index.md"
    with open(path, "r") as f:
        md = f.readlines()
    ruler = md.index("|  --  | --: |\n")
    md[ruler + 1] = s + "\n"

    with open(path, "w") as f:
        f.writelines(md)

# editing the md source in-place
def update_blog(s):
    path = "../pages/blog/_index.md"
    s = s + "\n"
    for l in fileinput.FileInput(path, inplace=1):
        if "--:" in l:
            l = l.replace(l, l + s)
        print(l, end=""),


# fetch title and date
meta = markdown_path(getrecent(blog), extras=["metadata"]).metadata
fname = os.path.basename(os.path.splitext(getrecent(blog))[0])
url = "/blog/" + fname
line = f"| [{meta['title']}]({url}) | `{meta['date']}` |"

update_index(line)
update_blog(line)

I’m going to skip explaining this one out, but in essence, it’s one massive hack. And in the end, that’s my point exactly. It’s very hacky, but the sheer amount I learnt by writing this ~50 line script can’t be taught anywhere.

This was partially how vite was born. It was originally intended to be a script to build my site, but grew into a full-blown Python package. I could’ve just used an off-the-shelf static site generator given that there are so many of them, but I chose to write one myself.

And that just about sums up what I wanted to say. The best and most fun way to learn to code—write hacky scripts. You heard it here.

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