Today I Learned

This repository tracks the snippets, notes, and ephemera that don't warrant a blog post but may prove useful later. Inspired by Josh Branchaud and Chuck Grimmet.

147 notes and counting...

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Categories

• Awk
• AWS
• Bash
• CSS
• Data Structures
• Docker
• Drupal
• ElasticSearch
• Git
• HTML
• JavaScript
• Jest
• Laravel
• Mac OS
• MongoDB
• MySQL
• Networking
• Node
• Numpy
• PHP
• PHPUnit
• Python
• React
• Rust
• SQLite
• SQL Server
• Theory
• Tmux
• TypeScript
• Unix
• Vagrant
• Video
• Vim

Awk

• Get index of character in string
• Set separator between print statements

AWS

• Query CloudFormation Stacks by tag
• Validate CloudFormation template

Bash

• Extract substrings from variables
• Get PID of shell running script
• Make an array of files from glob pattern
• Mark variables as readonly
• Use arrays in Bash

CSS

• Add unit at end of calc expression
• Load animation css separately based on user preference
• Target dark mode with media query
• Typeset numbers for tables with font-feature-settings
• Use font-display: swap; to render text in fallback font until @font-face font loads
• Use clamp to control values over a range

Data Structures

• Deque (double-ended queue)

Docker

• Prune unused images and volumes
• Start Bash inside container

Drupal

• Add an unlinked item to the breadcrumb in Drupal 8
• Dump all Twig variable names in the current context
• Import updated configuration without uninstalling module
• List all registered plugin IDs for blocks with Drush
• Get URL of current page in Drupal Twig
• Use optional configuration with modules

ElasticSearch

• List indices on an ElasticSearch cluster

Git

• Ammend previous commit message
• Create patches
• Discard untracked changes
• Do not paginate output of commands
• Get path to root of repository
• Hide untracked files in git status
• List branches merged (or not) with current branch
• Make new branch from stash
• Mark releases with tags
• Remove stale remote tracking branches
• Revert file to some previous commit
• Search across historical commit diffs
• See diff between current and last commit
• Sign commits with GPG
• Show only filenames in git log output
• Stash and unstash changes

HTML

• Semantically represent program output
• Set start number of ol tag

Jest

• Define window.location.href for an individual test
• Filter tests run by title

JavaScript

• Check if number type is a safe integer
• Convert an integer to hex, octal, or binary
• Detect Invalid Date objects
• Get color depth of screen
• Get epsilon value in Javascript
• ISO date strings without timezones are handled differently across browsers
• Make an enum-like structure with Object.freeze
• Maps keep key insertion order and are iterable
• Pad string with padStart
• Rename destructured variables
• Send message to parent window from iframe or popup
• Use postMessage API to send messages to Service Worker

Laravel

• Append computed Eloquent model properties to JSON responses
• Append query parameters to pagination links
• Create model, controller, and migration with one artisan command
• Run test without firing events
• Turn off exception handling in tests

Mac OS

• List available devices and runtimes in the Simulator App
• Show Hidden Files/Folders in Finder CMD + Shift + .

MongoDB

• Clear shell with cls command
• Dump database to archive

MySQL

• Dump database without locking
• Use group_concat to concatenate group results into a single string
• Perform case-sensitive string comparison with BINARY keyword
• Return first non-null value from set with COALESCE function
• See system configuration values
• See the schema of a table
• Show privileges for user
• Show currently running operations

Networking

• Filter Wireshark traffic by an IP address source
• Ping over a specific network interface with -I
• Set DNS server for dig command
• Use dig to query DNS information
• Query for types of DNS records with dig

Node

• Handle POSIX signals with callback
• Inspect large objects
• List all globally installed NPM packages
• List outdated packages with NPM outdated
• Pass data to all views in Express with res.locals object

Numpy

• Transpose a numpy array (matrix) with .T

PHP

• Assign many variables from an array with list
• Build http query string from an array with http_build_query
• Call function on script exit with register_shutdown_function
• Compact variables into an array
• Declare nullable types
• Desctructure named array values
• Format debug_backtrace as JSON
• Open REPL with -a option

PHPUnit

• Set a default test suite
• Set constants in config file
• Use data providers to provide variations on input

Python

• Extend behavior of functions with decorators
• Filter a list with list comprehension
• Profile program with cProfile
• Unpack sequences and collections with star operator
• Use union type hints

React

• Use class properties to simplify handler functions
• Run cleanup function with useEffect

Rust

• Format string output
• Use rustup to manage installed versions of Rust
• Run clippy (linter)

SQLite

• List tables and show schema from cli

SQL Server

• Hash values in SQL Server
• Parse string to date

Theory

• Use CAP Theorem to guide database choices
• Distinguish Nominal vs Structural subtypes

Tmux

• Send copied text to OS clipboard
• Zoom a panel to full terminal size

TypeScript

• Mimic nominal types with tags

Unix

• Add a user to a group
• Base64 encode/decode data with base64
• Check disk usage with du
• Check file mime type with file command
• Compress a directory with tar
• Convert text files from one character set to another with iconv
• Execute multiple commands with xargs
• Forward SSH Agent with connection with -A flag
• Get fingerpint of ssh key
• Peek at just headers of CSV file
• Print sorted disk usage across device
• Schedule a cron job to run every X minutes
• See differences between files with diff
• See list of files opened by processes with lsof
• See memory usage with free
• Send cookies with curl -b
• Test headers with curl

Vagrant

• Show list of environments

Video

• Convert an mp4 to a gif with ffmpeg
• Cut a clip from a video with ffmpeg
• Remove audio from video with ffmpeg -an

Vim

• Edit file in new tab
• Delete without overwriting yanked text
• Find current word forward or back
• Increment and decrement numbers
• Lowercase a series of words
• Open a file from filename or path in source code
• Open a file from netrw in new tab
• Open fzf result in new tab
• See list of suggested completions for current word
• Set the color scheme