Today I Learned (TIL)
TIL stands for today I learned. This is a collection of small, practical things I’ve learnt while writing software, which I thought were worth remembering and sharing with other people.
If you want to follow along, these posts have their own RSS feed.
You can filter by tag: applescript · aws · bash · buildkite · css · csv · curl · fish · flickr · github · github-actions · http · https · images · interesting-words · javascript · jekyll · jxa · liquid · live-text · macos · mastodon · naming-things · netlify · nginx · obsidian · photokit · podcasts · python · rsync · safari · shell-scripting · sparql · spreadsheets · sqlite · svg · swift · tumblr · unicode · wikimedia-commons · wordpress · youtube
These are the current filters.
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How to shuffle an array in a Jekyll template
If you want an array in random order, you can use the
samplefilter to get a random sample of the same size as the original array. -
Checking if a URL has changed when you fetch it over HTTP
When you make an HTTP request, you can use the
If-Modified-Sinceheader to get a 304 Not Modified if nothing has changed since your last request. -
The
opencommand can ask questionsIf you pass an argument that can’t be easily identified as a file or a URL,
openwill ask you what to do next. This may be a surprise if you were trying to use it in a script. -
Why is Pillow rotating my image when I save it?
Images can have orientation specified in their EXIF metadata, which isn’t preserved when you open and save an image with Pillow.
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How to change the name of an internal link in an Obsidian table
Escaping the pipe like
[[filename\|display text]]allows you to customise the of a link in a table. -
Getting a boto3 Session for an IAM role using Python
Why I use Sessions in boto3, and the Python function I use to create them.
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My config for running youtube-dl
The flags and arguments I find useful when I’m using youtube-dl.
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How much will Mastodon instances try to re-send messages?
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Get my Netlify bandwidth usage from the API
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How to restrict a page to specific IP addresses
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Use the
-n/-iflags to avoid overwriting files withcpandmv -
How to parse URLs in JXA
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Using
errexitand arithmetic expressions in bash -
How to check when an HTTPS certificate expires
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The COUNT(X) function only counts non-null values
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What happens when you replace a photo?
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Exclude files from Time Machine with
tmutil addexclusion -
You need to call
resp.close()to close the file opened bysend_file() -
Add the
-vflag to see whatrmis deleting -
Custom error pages in Flask
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Use the
{% raw %}tag to describe Liquid in LiquidIf you’re trying to write about using Liquid tags in a Liquid-based site, wrapping your tags in the
{% raw %}tag will prevent them being rendered. -
What characters are allowed in titles on Wikimedia Commons?
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Run a script on macOS on a schedule using a LaunchAgent
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Beware of using
test -nwith command expansion -
How to tally combinations of values across multiple columns
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How to move files when you need sudo on the remote server
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How to gracefully restart a gunicorn app
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How to find the longest common suffix in a list of strings in Python
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How to simulate shell pipes with the subprocess module
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Use the
{% capture %}tag to assign complex strings to variablesIf you want to get a string that’s semi-complicated to construct, you can put a “mini-template” in the
{% capture %}tag to build it over multiple lines. -
How to create a footer that’s always at the bottom of the page
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WordPress URLs that get hammered by spammers
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Manage MP3 metadata from iTunes with eyed3
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Sort a list of DOM elements by sorting and calling
appendChild() -
How to create flag emojis for countries in Python
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Use the IMAGE function to insert an image into a spreadsheet
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How to style a
<details>element differently depending on whether it’s open or closed -
Pausing the animation of <svg> elements can affect child <svg> elements differently in different browsers
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Create a directory before you
cpormva file to it -
Running the Netlify CLI in GitHub Actions
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Use shlex.split() to parse log files quickly
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Use the regex library to get Unicode property escapes in Python
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Get and manipulate the contents of a page in Safari with
"do JavaScript" -
SVGs are only rendered on GitHub if you use an
<img>that points to another file -
Animate an attribute of an element with <animate>
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Run a randomly selected subset of tests with pytest
By reading the code for the
pytest-random-orderplugin, I was able to write a new plugin that runs a random subset of tests. -
Getting a tally of SQLite values as a CSV
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Using sqlite-utils to convert a CSV into a SQLite database
You can use sqlite-utils on the command line to create a SQLite database from a CSV file.
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Python’s sqlite3 context manager doesn’t close connections
The
sqlite3.connect(…)context manager will hold connections open, so you need to remember to close it manually or write your own context manager. -
How to delete albums
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Live Text is aware of how hyphenation works (kinda)
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Go between M-IDs and filenames on Wikimedia Commons
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How to do resumable downloads with curl
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Find files that use a particular SDC field
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Why the term “snak” keeps appearing in the Wikidata API
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The acronym “woe” in the Flickr API stands for “Where On Earth”
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Use Unicode property escapes to detect emoji in JavaScript
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Use concurrency gates to prevent concurrent deployments
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How to profile Swift code
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Calley-ope (calliope) Syndrome is pronouncing a word wrong because you’ve only ever read it on the page
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How to set the clock on a Tricity Bendix SIE454 electric cooker
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How to set the clock on a Worcester 28CDi boiler
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Get an RSS feed of external audio posts on Tumblr
If you add
/podcastto a Tumblr site, you get a podcast-like RSS feed for all the external audio posts on that site.