lowesusannah/til

:memo: Today I Learned

TIL

Today I Learned

A collection of concise write-ups on small things I learn day to day across a variety of languages and technologies. These are things that don't really warrant a full blog post. These are mostly things I learn by pairing with smart people at Hashrocket.

For a steady stream of TILs from a variety of rocketeers, checkout til.hashrocket.com.

649 TILs and counting...

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Categories

• Ack
• Chrome
• Clojure
• CSS
• Devops
• Elixir
• Git
• Go
• Internet
• JavaScript
• Linux
• Mac
• MySQL
• Phoenix
• PostgreSQL
• Rails
• React
• ReasonML
• Ruby
• tmux
• Unix
• Vim
• VSCode
• Webpack
• Workflow

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Ack

• ack --bar
• Case-Insensitive Search
• List Available File Types

Chrome

• Access A Value Logged To The Console
• Easier Access To Network Throttling Controls
• Pretty Print Tabular Data
• Reference The Selected Node
• Selecting DOM Elements Faster Than Ever
• Simulating Various Connection Speeds
• Toggle Device Mode
• Toggle Open The Console Drawer

Clojure

• Aggregation Using merge-with
• Argument Requirements For A Function
• Combinations Of Items From A Sequence
• Define Something Only Once
• Evaluate One Liners With lein-exec
• Expanding Macros
• Get The Value Of An Environment Variable
• List Functions For A Namespace
• Load A File Into The REPL
• Mapping With An Index
• Open JavaDocs
• Pretty Print The Last Thing
• Quick Clojure Docs
• Reductions
• Set Max Heap Size
• Specify the Directory of a Shell Command
• Splitting On Whitespace
• Swap Two Items in a Vector
• Try A Clojure Project In The REPL
• Type of Anything
• When Overflow Is Desired

CSS

• Apply Styles To The Last Child Of A Specific Type
• Dry Up SCSS With Mixins
• Lighten And Darken With CSS Brightness Filter
• Lighten And Darken With SCSS
• Parameterized SCSS Mixins

Devops

• Aliasing An Ansible Host
• Check The Status of All Services
• Check The Syntax Of nginx Files
• Determine The IP Address Of A Domain
• Path Of The Packets
• Push Non-master Branch To Heroku
• Reload The nginx Configuration
• Running Out Of inode Space
• Wipe A Heroku Postgres Database

Elixir

• Append To A Keyword List
• Assert An Exception Is Raised
• Binary Representation Of A String
• Check For A Substring Match
• Compute md5 Digest Of A String
• Counting Records With Ecto
• Create A Date With The Date Sigil
• Create A List Of Atoms
• Creating A PID
• Creating Indexes With Ecto
• Defining Multiple Clauses In An Anonymous Function
• Determine The Latest Release Of A Hex Package
• Do You Have The Time?
• Do You Have The Time? - Part 2
• Documentation Lookup With Vim And Alchemist
• Dynamically Generating Atoms
• Execute Raw SQL In An Ecto Migration
• Expose Internal Representation
• Include Captures With String.split
• Inspecting The Process Message Queue
• List Functions For A Module
• Listing Files In IEx
• Pattern Matching In Anonymous Functions
• Quitting IEx
• Range Into List Using Comprehensions
• Referencing Values In IEx's History
• Remove One List From Another
• Replace Duplicates In A Keyword List
• Requiring Keys For Structs
• Reversing A List
• Reversing A List - Part 2
• Root Directory Of A Project
• Round Floats To Integers
• Run ExUnit Tests In A Deterministic Order
• Same Functions Should Be Grouped Together
• String Interpolation With Just About Anything
• Unique Indexes With Ecto
• Updating Values In A Map
• Virtual Fields With Ecto Schemas
• Word Lists For Atoms

Git

• Accessing a Lost Commit
• Amend Author Of Previous Commit
• Caching Credentials
• Checking Commit Ancestry
• Checkout Old Version Of A File
• Checkout Previous Branch
• Cherry Pick A Range Of Commits
• Clean Out All Local Branches
• Clean Up Old Remote Tracking References
• Clone A Repo Locally From .git
• Delete All Untracked Files
• Determine The Hash Id For A Blob
• Diffing With Patience
• Dry Runs in Git
• Excluding Files Locally
• Find The Initial Commit
• Get The Short Version Of The Latest Commit
• Grab A Single File From A Stash
• Grep For A Pattern On Another Branch
• Grep Over Commit Messages
• Ignore Changes To A Tracked File
• Include Some Stats In Your Git Log
• Intent To Add
• Interactively Unstage Changes
• Last Commit A File Appeared In
• List All Files Changed Between Two Branches
• List Different Commits Between Two Branches
• List Filenames Without The Diffs
• List Most Git Commands
• List Untracked Files
• Move The Latest Commit To A New Branch
• Rebase Commits With An Arbitrary Command
• Reference A Commit Via Commit Message Pattern Matching
• Rename A Remote
• Renaming A Branch
• Resetting A Reset
• Show All Commits For A File Beyond Renaming
• Show File Diffs When Viewing Git Log
• Show List Of Most Recently Committed Branches
• Show The diffstat Summary Of A Commit
• Show The Good And The Bad With Git Bisect
• Single Key Presses in Interactive Mode
• Staging Changes Within Vim
• Staging Stashes Interactively
• Stashing Only Unstaged Changes
• Stashing Untracked Files
• Untrack A Directory Of Files Without Deleting
• Untrack A File Without Deleting It
• Update The URL Of A Remote
• Verbose Commit Message
• Viewing A File On Another Branch
• What Changed?
• What Is The Current Branch?
• Whitespace Warnings

Go

• Access Go Docs Offline
• Build For A Specific OS And Architecture
• Not So Random
• Replace The Current Process With An External Command
• Sleep For A Duration
• Upgrading From An Older Version On Mac

Internet

• Add Emoji To GitHub Repository Description
• Exclude Whitespace Changes From GitHub Diffs
• Focus The URL Bar
• Search Tweets By Author
• Show All Pivotal Stories With Blockers

JavaScript

• Accessing Arguments To A Function
• Character Codes from Keyboard Listeners
• Computed Property Names In ES6
• Create An Array Containing 1 To N
• Create Bootstrapped Apps With Yarn
• Custom Type Checking Error Messages With Yup
• Default And Named Exports From The Same Module
• Destructuring The Rest Of An Array
• Enable ES7 Transforms With react-rails
• Expand Emojis With The Spread Operator
• Fill An Input With A Ton Of Text
• Freeze An Object, Sorta
• Get The Location And Size Of An Element
• Globally Install A Package With Yarn
• Immutable Remove With The Spread Operator
• Initialize A New JavaScript Project With Yarn
• Install The Latest Version Of Node With Nvm
• ISO-8601 Formatted Dates Are Interpreted As UTC
• Link A JavaScript Package Locally
• List Top-Level NPM Dependencies
• Matching Multiple Values In A Switch Statement
• New Dates Can Take Out Of Bounds Values
• Numbers Are Empty
• Object Initialization With Shorthand Property Names
• Random Cannot Be Seeded
• Render An Array Of Elements With React 16
• Running ES6 Specs With Mocha
• Scoping Variables With A Block Statement
• Splat Arguments To A Function
• Spread The Rest With ES6
• String Interpolation With Template Literals
• Throttling A Function Call
• Timing Processes
• Transforming ES6 and JSX With Babel 6
• Truthiness of Integer Arrays
• Waiting On Multiple Promises
• Who Am I: NPM Edition
• Yarn Commands Without The Emojis
• Yup Schemas Are Validated Asynchronously

Linux

• Check Ubuntu Version
• Configure Your Server Timezone
• List The Statuses Of All Upstart Jobs
• Upgrading Ubuntu

Mac

• Clean Up Old Homebrew Files
• Default Screenshot Location
• Display A Message With Alfred
• Insert A Non-Breaking Space Character
• List All The Say Voices
• Require Additional JS Libraries In Postman
• Resizing Both Corners Of A Window
• Run A Hardware Check

MySQL

• Display Output In A Vertical Format
• Dump A Database To A File
• List Databases And Tables
• Show Create Statement For A Table
• Show Tables That Match A Pattern
• Show Indexes For A Table

Phoenix

• Bypass Template Rendering
• Check The Installed Version
• Generate New App Without Brunch
• Render A Template To A String
• Serve Static Assets From Custom Directory
• Specifying The Digest Directory
• Specifying The Server Port

PostgreSQL

• A Better Null Display Character
• Add ON DELETE CASCADE To Foreign Key Constraint
• Adding Composite Uniqueness Constraints
• Aggregate A Column Into An Array
• Assumed Radius Of The Earth
• Auto Expanded Display
• Between Symmetric
• Capitalize All The Words
• Change The Current Directory For psql
• Checking Inequality
• Checking The Type Of A Value
• Clear The Screen In psql
• Clear The Screen In psql (2)
• Compute Hashes With pgcrypto
• Compute The md5 Hash Of A String
• Configure The Timezone
• Constructing A Range Of Dates
• Count Records By Type
• Create A Composite Primary Key
• Create hstore From Two Arrays
• Create Table Adds A Data Type
• Creating Conditional Constraints
• Creating Custom Types
• Day Of Week By Name For A Date
• Day Of Week For A Date
• Default Schema
• Defining Arrays
• Determining The Age Of Things
• Dump And Restore A Database
• Edit Existing Functions
• Escaping A Quote In A String
• Escaping String Literals With Dollar Quoting
• Export Query Results To A CSV
• Extracting Nested JSON Data
• Find The Data Directory
• Find The Location Of Postgres Config Files
• Fizzbuzz With Common Table Expressions
• Generate A UUID
• Generate Series Of Numbers
• Generating UUIDs With pgcrypto
• Get The Size Of A Database
• Get The Size Of A Table
• Get The Size Of An Index
• Getting A Slice Of An Array
• Insert Just The Defaults
• Integers In Postgres
• Intervals Of Time By Week
• Is It Null Or Not Null?
• Limit Execution Time Of Statements
• List All Columns Of A Specific Type
• List All Rows In A Table
• List All The Databases
• List All Versions Of A Function
• List Available Schemas
• List Connections To A Database
• List Database Objects With Disk Usage
• List Database Users
• List Various Kinds Of Objects
• Lower Is Faster Than ilike
• Max Identifier Length Is 63 Bytes
• pg Prefix Is Reserved For System Schemas
• Prepare, Execute, And Deallocate Statements
• Pretty Print Data Sizes
• Pretty Printing JSONB Rows
• Print The Query Buffer In psql
• Renaming A Sequence
• Renaming A Table
• Restart A Sequence
• Restarting Sequences When Truncating Tables
• Salt And Hash A Password With pgcrypto
• Send A Command To psql
• Set Inclusion With hstore
• Set A Seed For The Random Number Generator
• Sets With The Values Command
• Show All Versions Of An Operator
• Sleeping
• Special Math Operators
• Storing Emails With citext
• String Contains Another String
• Temporarily Disable Triggers
• Temporary Tables
• Terminating A Connection
• Timestamp Functions
• Toggling The Pager In PSQL
• Truncate All Rows
• Truncate Tables With Dependents
• Turning Timing On
• Two Ways To Compute Factorial
• Types By Category
• Use A psqlrc File For Common Settings
• Use Argument Indexes
• Use Not Valid To Immediately Enforce A Constraint
• Using Expressions In Indexes
• Using Intervals To Offset Time
• Who Is The Current User
• Word Count for a Column
• Write A Query Result To File

Rails

• Add React With Webpacker To A New Rails App
• Advance The Date
• All or Nothing Database Transactions
• Attach A File With Capybara
• Attribute Getter without the Recursion
• Attribute Was
• Autosave False On ActiveRecord Associations
• Capybara Page Status Code
• Change The Nullability Of A Column
• Code Statistics For An Application
• Conditional Class Selectors in Haml
• Convert A Symbol To A Constant
• Creating Records of Has_One Associations
• Custom Validation Message
• Demodulize A Class Name
• Generating And Executing SQL
• Hash Slicing
• Ignore Poltergeist JavaScript Errors
• List The Enqueued Jobs
• Mark For Destruction
• Migrating Up Down Up
• Params Includes Submission Button Info
• Perform SQL Explain With ActiveRecord
• Polymorphic Path Helpers
• Pretend Generations
• Read-Only Models
• Remove The Default Value On A Column
• Rescue From
• Retrieve An Object If It Exists
• Select A Select By Selector
• Select Value For SQL Counts
• Set Schema Search Path
• Show Pending Migrations
• Show Rails Models With Pry
• Show Rails Routes With Pry
• Truncate Almost All Tables
• Where Am I In The Partial Iteration?

React

• A Component Is Just A Bag Of Data
• Accessing Env Vars In create-react-app
• Alter The Display Name Of A Component
• create-react-app Comes With Lodash
• Defining State In A Simple Class Component
• Destructure Variables As Props To A Component
• Dispatch Anywhere With Redux
• Dynamically Add Props To A Child Component
• Force A Component To Only Have One Child
• Inactive And Active Component Styles With Radium
• Inline Style Attributes Should Be Camel Cased
• Mapping Over One Or Many Children
• Passing Props Down To React-Router Route
• Proxy To An API Server In Development With CRA
• Quickly Search For A Component With React DevTools
• Read Only Input Elements
• Rendering Multiple Nodes With Fragments
• Use A Ref To Autofocus An Input
• Use withRouter To Pass Down React-Router History
• Visually Select A React Element For Inspection
• Who Is Your Favorite Child?

ReasonML

• Defining Variants With Constructor Arguments
• Exhaustive Pattern Matching Of List Variants
• Helping The Compiler Help Us With Variants
• Inline Component Styles With Reason React
• Multi-Argument Functions As Syntactic Sugar
• Pattern Match On Exceptions
• Quickly Bootstrap A React App Using Reason
• Seeding And Generating Random Integers
• String Interpolation With Integers And Sprintf
• String Interpolation With Quoted Strings

Ruby

• Are They All True?
• Assoc For Hashes
• Block Comments
• Chaining Multiple RSpec Change Matchers
• Colorful Output With MiniTest
• Comparing Class Hierarchy Relationships
• Comparing Arrays In RSpec
• Construct A Constant From A String
• Create an Array of Stringed Numbers
• Create A Hash From An Array Of Arrays
• Create Thumbnail Image For A PDF
• Defaulting To Frozen String Literals
• Destructuring Arrays In Blocks
• Disassemble Some Codes
• Double Splat To Merge Hashes
• Edit Previous Parts Of The Pry Buffer History
• Editing Code In Pry
• Evaluating One-Off Commands
• FactoryGirl Sequences
• Fail
• Finding The Source of Ruby Methods
• Identify Outdated Gems
• If You Detect None
• Ins And Outs Of Pry
• Invoking Rake Tasks Multiple Times
• Last Raised Exception In The Call Stack
• Limit Split
• Listing Local Variables
• Navigate Back In The Browser With Capybara
• Next And Previous Floats
• Or Operator Precedence
• Override The Initial Sequence Value
• Parallel Bundle Install
• Pass A Block To Count
• Passing Arbitrary Methods As Blocks
• Passing Arguments To A Rake Task
• Percent Notation
• Question Mark Operator
• Rake Only Lists Tasks With Descriptions
• Rendering ERB
• Replace The Current Process With An External Command
• Require Entire Gemfile In Pry Session
• Rerun Only Failures With RSpec
• Returning With Sequel
• Running A Single MiniTest Example
• Safe Navigation Operator
• Scroll To Top Of Page With Capybara
• Set RVM Default Ruby
• Show Public Methods With Pry
• Squeeze Out The Extra Space
• String Interpolation With Instance Variables
• Summing Collections
• Uncaught Exceptions In Pry
• undef_method And The Inheritance Hierarchy
• Up And Down With Integers
• Use A Case Statement As A Cond Statement
• Use dotenv In A Non-Rails Project
• Who Are My Ancestors?
• Zero Padding

tmux

• Adjusting Window Pane Size
• Break Current Pane Out To Separate Window
• Create A Named tmux Session
• Create A New Session In A New Server
• Cycle Through Layouts
• Enabling Vi Mode
• Hiding The Status Bar
• Jumping Between Sessions
• Kill Other Connections To A Session
• Kill The Current Session
• List All Key Bindings
• List Sessions
• Open New Window With A Specific Directory
• Organizing Windows
• Paging Up And Down
• Pane Killer
• Reclaiming The Entire Window
• Rename The Current Session
• Swap Split Panes
• tmux in your tmux

Unix

• All The Environment Variables
• Cat A File With Line Numbers
• Change Default Shell For A User
• Change To That New Directory
• Check If A Port Is In Use
• Check The Current Working Directory
• Clear The Screen
• Command Line Length Limitations
• Copying File Contents To System Paste Buffer
• Create A File Descriptor with Process Substitution
• Curling For Headers
• Curling With Basic Auth Credentials
• Display All The Terminal Colors
• Display Free Disk Space
• Do Not Overwrite Existing Files
• Exclude A Directory With Find
• File Type Info With File
• Find Newer Files
• Forward Multiple Ports Over SSH
• Get The Unix Timestamp
• Global Substitution On The Previous Command
• Globbing For All Directories In Zsh
• Globbing For Filenames In Zsh
• Grep For Files Without A Match
• Grep For Multiple Patterns
• Hexdump A Compiled File
• Jump To The Ends Of Your Shell History
• Kill Everything Running On A Certain Port
• Killing A Frozen SSH Session
• Last Argument Of The Last Command
• Less With Style
• List All Users
• List Files Ordered By Modification Date
• List Names Of Files With Matches
• List Of Sessions To A Machine
• List Parent pid With ps
• List The Available JDKs
• Map A Domain To localhost
• Only Show The Matches
• Open The Current Command In An Editor
• Partial String Matching In Bash Scripts
• PID Of The Current Shell
• Repeat Yourself
• Saying Yes
• Search Files Specific To A Language
• Search History
• Search Man Page Descriptions
• Securely Remove Files
• Show Disk Usage For The Current Directory
• Show The Size Of Everything In A Directory
• SSH Escape Sequences
• SSH With Port Forwarding
• Sort In Numerical Order
• Switch Versions of a Brew Formula
• Undo Some Command Line Editing
• View A Web Page In The Terminal
• Watch The Difference
• Watch This Run Repeatedly
• Where Are The Binaries?

Vim

• Absolute And Relative Line Numbers
• Add A File Without Loading It
• Add Custom Dictionary Words
• Almost The End Of The Line
• Alternate Files With vim-rails
• Amend Commits With Fugitive
• Backspace Options
• Beginning And End Of Previous Change
• The Black Hole Register
• Blank Lines Above And Below
• Breaking The Undo Sequence
• Buffer Time Travel
• Build And Install A Go Program
• Case-Aware Substitution With vim-abolish
• Case-Insensitive Substitution
• Center The Cursor
• Check For An Executable
• Check Your Current Color Scheme
• Close All Other Splits
• Close All Other Windows
• Close the Current Buffer
• Coerce The Current Filetype
• Coercing Casing With vim-abolish
• Count the Number of Matches
• Create A New Directory In netrw
• Create A New File In A New Directory
• Creating Non-Existent Directories
• Default netrw To Tree Liststyle
• Delete Every Other Line
• Delete Lines That Match A Pattern
• Delete To The End Of The Line
• Deleting Buffers In BufExplorer
• Deleting Directories Of Files From netrw
• Detect If You Are On A Mac
• Difference Between :wq and :x
• Display Word Count Stats
• Edges Of The Selection
• End Of The Word
• Escaping Terminal-Mode In An Nvim Terminal
• Filter Lines Through An External Program
• Fix The Spelling Of A Word
• Fold A Visual Selection And Expand It Back
• Format Long Lines To Text Width
• From Ruby Variables To JavaScript Variables
• Generate and Edit Rails Migration
• Get The pid Of The Session
• Go To File With Line Number
• Grepping Through The Vim Help Files
• Head of File Name
• Help For Non-Normal Mode Features
• Highlighting Search Matches
• Horizontal to Vertical and Back Again
• Increment All The Numbers
• Incremental Searching
• Interact With The Alternate File
• Interactive Buffer List
• Joining Lines Together
• Jump To Matching Pair
• Jump To The Next Misspelling
• List All Buffers
• List Of Plugins
• Load A Directory Of Files Into The Buffer List
• Marks Across Vim Sessions
• Match The Beginning And End Of Words
• Moving To A Specific Line
• Navigating By Blank Lines
• NETRW Listing Styles
• Next Modified Buffer
• Open A Tag In A Split Window
• Open an Unnamed Buffer
• Open Routes File With vim-rails
• Open The Directory Of The Current File
• Open The Gemfile
• Open The Latest Rails Migration
• Open Vim To A Tag Definition
• Opening a URL
• Opening Man Pages In Vim
• Paste A Register From Insert Mode
• Preventing Typos with Abbreviations
• Previous Buffer
• Previous Visual Selection
• Print Version Information
• Quick File Info
• Quick Man Pages
• Quick Quickfix List Navigation
• Quickly Switch To A Buffer By Number
• Re-indenting Your Code
• Read In The Contents Of A Rails File
• Rename Current File
• Repeat The Previous Change
• Repeating Characters
• Replace A Character
• Reset Target tslime Pane
• Reverse A Group Of Lines
• Rotate Everything By 13 Letters
• Running Bundle With vim-bundler
• Scrolling Relative to the Cursor
• Searching For Hex Digits
• Set End Of Line Markers
• Set Your Color Scheme
• Setting Filetype With Modelines
• Show All Syntax Highlighting Rules
• Show Matching Entries For Help
• Split Different
• Split The Current Window
• Splitting For New Files
• Swap Occurrences Of Two Words
• Swapping Split Windows
• Tabs To Spaces
• The Vim Info File
• Toggle Absolute And Relative Paths In BufExplorer
• Toggling Syntax Highlighting
• Turning Off Search Highlighting
• Unloading A Buffer
• Use Active Window With BufExplorer
• Verbose Commits With Fugitive
• View Commit History of a File
• Viewing Man Pages with man.vim
• Vim Without The Extras
• What Is On The Runtime Path?
• Whole Line Auto-Completion
• Wrap With Some Room

VSCode

• Open An Integrated Terminal Window
• Toggle Between Terminals

Webpack

• Better Module Imports With Aliases
• Debugging With Full Source Maps
• Run ESLint As A Preloader
• Specify Port Of CRA's Webpack Dev Server
• Use A Specific Config File

Workflow

• Convert An ePub Document To PDF On Mac
• Toggle Between Stories In Storybook

Usage

The .vimrc file for this project contains a function CountTILs that can be invoked with <leader>c. This will do a substitution count of the current number of TILs and display the result in the command tray.

About

I shamelessly stole this idea from thoughtbot/til.

Other TIL Collections

• Today I Learned by Hashrocket
• jwworth/til
• thoughtbot/til

License

© 2015-2018 Josh Branchaud

This repository is licensed under the MIT license. See LICENSE for details.