Dev How To

Intro

This project is a compilation of my own work mixed with ideas and notes I learn from others. You’ll find pages with tutorial-like explanations on things that interest me and code solutions for book exercises, coding challenges, algorithms and data structures, functional programming stuff, etc.

If you find any problems, or have suggestions, you are welcome to create an issue or a pull request in the Dev How To Gitlab repository.

Licensing Information

The text in this site is licensed under Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) and the code under the General Public License v3.

The source code for this project is located at the Dev How To Gitlab repository.

Table of Contents

• Command Line
  • Intro
  • Single Unix Specification (SUS)
    • Yes, That Website Sucks
  • GNU Coreutils
    • Man, Info and Help
      • help
      • info
        • info summary
      • man
        • Finding Info Node Names
      • `cp’ Man Page Example
      • `csi’ -help Example
      • Command Options
      • POSIX and GNU
      • Documentation Relationships
        • End of Options echo Example
      • Other Links and Resources
    • Shell Built-In Commands
      • Intro
      • POSIX builtin reserved word
      • Shells implementation of builtin
    • Shell Argument Syntax
      • Whitespace and Quoting
        • A Sad rm Incident
      • End Of Options ‘--’
        • remove files starting with ‘-’
    • echo and printf
      • Intro
      • echo
        • echo and newline
        • How to print ‘-n’?
        • Prefer printf instead of echo
      • printf
        • Format operand reutilization
    • Redirections
      • cat STDIN and redirect to file
    • Bash Brace Expansion
      • Moving (renaming) files
    • Bash Parameter Expansion
      • remove newline
    • Bash Aliases
      • Intro
      • How To Unalias‽
      • Manually Expanding Aliases
      • Tricky aliases 😮
    • Bash Arrays
      • Serialize and Store Bash Array to a File
      • Deserialize Bash Array From a File
        • Using mapfile
        • Why can’t we use read‽
        • Understanding mapfile vs read
        • IFS= and \0
        • field separator vs terminator
      • Serialize a NUL-separated list of files to a variable
    • Terminal Emulators
      • Kitty
        • Login Shell and Startup RC Files
        • Single vs Multiple Kitty Windows
        • Setting Title
        • Themes
          • Vim + Kitty + Solarized Light
      • Indices and tables
    • grep - Global Regular Expression and Print
      • Intro
      • Search in files with given extensions
      • Exclude certain directories
    • tar | Command Line
      • Pack Excluding Directories
    • Useful find examples
      • Find files and store in array
    • du Command
      • Sort
      • Sort by disk usage in descending order
    • HackerRank Shell
      • Intro
      • Easy Challenges
        • Let’s Echo
        • Looping With Numbers
        • Looping And Skipping
        • A Personalized Echo
        • The World of Numbers
        • Getting started with conditionals
        • More on Conditionals
        • Arithmetic Operations
        • Compute the Average
        • cut Challenges
        • Head of Text File Challenges
        • Middle of a Text File
        • Tail of a Text File 1 and 2
        • tr Command 1
        • tr Command 2
        • tr Command 3
        • sort Lines Challenges
        • uniq Challenges
        • Read In An Array
        • Display an Element of an Array
        • Count Elements in an Array
        • Slice An Array
        • Concatenate Array With Itself
        • grep A
        • grep B
        • sed 3
        • sed 4
      • Medium Challenges
        • Paste 1
        • paste 2
        • paste 3
        • paste 4
        • sed 1
        • sed 2
        • grep challenges
        • awk challenges
        • Filter an Array With Patterns
        • Remove First Capital Letter From Each Array Element
      • Hard Challenges
        • sed 5
        • Lonely Integer
        • Fractal Tree
      • The End
• Git
  • Commit Messages
    • Introduction
    • One lamentable episode
    • References
  • More Commit Message Examples
    • Detailed commit message with ASCII drawing
    • fzf Junegunn Choi Awesome Commit Message
  • Reset
    • Introduction to git reset
  • Git Branching
    • git checkout -b
  • Git Merge
    • Fast-forward merge branch without checkout
  • Git Revisions
    • Upstream and remote tracking branches
    • References
• Indices and tables
• Text Editors
  • Emacs
    • Installing on macOS
      • emacs-plus
        • Emacs Practical Editing Examples
          • Searching the buffer for…
          • the word under point
          • string under point
          • References
        • Emacs Org-Mode Tips
          • RET indents
  • Vim
    • CoC LSP
      • Ruby
        • References
    • Search and Replace Until Next UpperCase Char
      • Some Thoughts
      • TL;DR command
      • References
    • Neovim Telescope Tips
• Haskell
  • Intro
  • Identifier names
    • Syntax
      • concat to cons
    • Haskell Sectioning
      • Intro
      • question 2
      • Basic Syntax
      • Subtraction vs Negation
    • Haskell Programming From First Principles (book)
      • 04 - Data Types
        • Datatypes
        • Data Types Questions and Answers
          • types aka
          • enumerate types
          • values and types
          • data declarations
          • basic data declaration
      • ch09 Exercises :: Lists
        • Will it blow up?
          • Exercise 01
          • Exercise 02
          • Exercise 03
          • Exercise 04
          • Exercise 05
          • Exercise 06
          • Exercise 07
          • Exercise 08
          • Exercise 09
          • Exercise 10
        • Is it in normal form?
          • Exercise 01
          • Exercise 02
          • Exercise 03
          • Exercise 04
          • Exercise 05
          • Exercise 06
          • Exercise 07
        • More Bottoms
          • Exercise 01
          • Exercise 02
          • Exercise 03
          • Exercise 04
          • Exercise 05
          • Exercise 06
        • Exercises: Filtering
          • Exercise 1
          • Exercise 2
          • Exercise 3
        • Zipping exercises
          • Exercise 1
          • Exercise 2
        • Exercise 3
          • Solution 1
        • Chapter exercises
          • Data.Char
          • Ciphers
          • Writing your own standard functions
• Ruby
  • Ruby Concepts and Ideas
  • Bits and Bytes of Syntax Suggar
    • Hash Values
    • Map and Hash to Proc to Get Values
    • Hash Transform Values and &:next to_proc
      • Unit Tests | Ruby
        • Warning “circular require considered harmful”
      • RSpec | Ruby
        • Assert STDOUT output
          • References
      • Scope | Ruby
        • File Local Variables
      • HackerRank Ruby Tutorial
        • Hello World
        • self
        • methods
          • Monkey Patch Integer and create `range?’
        • Accessing Array Elements
        • Modifying Arrays
        • Filtering Arrays
        • Hashes
        • unless
        • loop, break if
        • group_by
          • Hash Gotcha!
        • Arrays
        • Currying
        • Lazy
          • Lazy Array of Powers
          • Lazy Array of Palindromic Primes
        • Blocks
        • Procs
        • Lambdas
        • Closures
          • Example 1 (remembers x)
          • Example 2 (error)
          • Example 3 (remembers 2nd x)
        • Currying and Partial Application
        • Arguments and Splat Operator
        • Keyword Arguments
          • Temperature Converter
        • String Indexing
          • Accessing
          • Mutating, Changing
          • Serial Average
        • String Iteration
          • Count Multibyte Chars
        • String Methods I
        • String Methods II
        • Enumerables ‘each_with_index’
        • rot13, map, collect
        • Enumerable reduce, inject
        • Enumerables any, all, none, find
          • any
          • all
          • none
          • find
          • Solution for the challenge
        • String Encoding
        • Methods Intro
        • Method Arguments
        • Ruby Enumerable Intro
      • Bundler | Ruby
        • Error Could not find gem ‘pry-doc
      • RVM | Ruby
        • `rvm list known’ not showing latest rubies
        • Default Ruby on New Shells
      • Pry | Ruby
        • show-doc
• Ruby on Rails
  • Command Line | Ruby on Rails
    • Basic Commands
  • Ruby on Rails and Docker
    • bundler “/ is not writable”
    • Can’t run tests
  • Unit Tests | Ruby on Rails
    • assert_equal wrong number args
  • Models and Migrations | Ruby on Rails
    • Creating models and migrations
    • Operations on the model
    • Errors
• PureScript
  • PureScript Resources
  • Useful Libraries
    • Read, Eval, Print, Loop: REPL
      • Intro
      • :type
      • :kind
    • Type Signatures
      • Fully Polymorphic, Unconstrained Types
      • Example 1
      • Example 2
    • Functions
      • Intro Notes
      • Lambda Expression
      • Aliasing functions to infix symbol
      • Currying and Partial Application
        • The Quintessential “add 1” Example
        • Example with replace
    • Modules
      • Importing a type and its data constructors
      • SomeType(..) syntax
      • References
    • Types
      • Char and String Types
        • Char
        • String
        • Unicode
          • Char
          • String
      • Data Types
        • Product and Coproduct types
        • Type Variables
        • :kind
        • More examples
      • Number Types
        • Typing a number
        • Negative Numbers
        • References
    • Char and String Types
      • Char
      • String
      • Unicode
        • Char
        • String
    • Number Types
      • Typing a number
      • Negative Numbers
      • References
    • Data Types
      • Product and Coproduct types
      • Type Variables
      • :kind
      • More examples
    • Lists
      • Basic Syntax for Creating Lists
      • References
    • PureScript Explained
      • const
        • const v1
        • const v2
        • const v3
        • const usage
          • with filter
      • apply, ‘$’
        • Using $ (dollar symbol) infixr apply operator
      • applyFlipped, ‘#’
        • Using ‘#’ (number/hash/pound symbol) infixl applyFlipped operator
      • Cons (Data.List)
        • Manually Create a List
• JavaScript
  • Logging
    • Free static function
  • Arrays
    • Array of n elements
    • Return array with conditional item
  • Async Examples with Ramda
    • Fetch and Pick Keys
  • Do It With Ramda Part I
    • Find users by name
  • Gotchas, Surprises and Pain Points | JavaScript
    • JavaScript Is Fun
  • JavaScript Performance
    • Introduction
    • Copy Array: push() vs …spread
      • Setup
      • Array of Random Numbers
      • push()
      • Spread
      • Explanation
      • Conclusion
    • Other Resources
  • LeetCode 30 Days of JavaScript
    • Introduction
    • Performance
    • Closures
      • Hello
      • Counter
      • To Be Or Not To Be (Expect)
      • Counter II
    • Basic Array Transformations
      • Apply Transform Over Each Element in Array (map())
      • Filter Elements from Array (filter())
      • Array Reduce Transformation (reduce())
        • Using Good Old for Loop
        • Using Recursion
      • Function Composition (compose())
        • for loop
        • reduceRight()
      • Return Length of Arguments Passed
• TypeScript
  • Tips For Learning TypeScript
  • TypeScript Two Responsibilities
  • Other Resources
    • tsconfig.json Examples
      • Simplest tsconfig.json 1
      • Simplest tsconfig.json 2
    • Structural Typing
      • Introduction
      • Type compatibility
        • Excess property checks
    • Any and Unknown Top Types
      • Introduction
      • any
      • Operations on any
      • Operations on unknown
    • Type Aliases and Interfaces
      • Introduction
      • Example Interface vs Type Alias
      • Interface Declaration Merging
      • Declaration Merging Danger
    • Object Types
      • Introduction
      • Non-null and non-undefined type {}
      • object type
      • Object type
    • Union Types
      • never
      • Unions with the empty set ∅
      • Union of some type and any
    • Intersection Types
      • Introduction to Intersection Types
        • Intersection of non non-object types
        • Intersection of object types
    • keyof
      • keyof D2 example
      • keyof D3 example index signature
      • keyof with getProp() function
      • keyof in type predicates
      • keyof with mapped types
        • Partial type utility
        • Required type utility
      • References
    • Mapped Types
    • Functions | TypeScript
      • Matching the type
        • A refresher on JavaScript function arguments
    • infer keyword | TypeScript
      • ReturnType
        • Some Details
      • Back to ReturnType
      • Examples Explained
        • FirstArg Type Utility
        • SecondArg Type Utility
        • ArrayItemType Type Utility
      • UnboxObjType, `infer’ in Co-variant Position
    • React Component-Related Types
      • React.ReactElement
      • JSX.Element
      • React.ReactNode
      • Links and Resources
• Scheme
  • Building and Installing Chicken Scheme 5.3.0rc3 on macOS Big Sur
    • Downloading and Unpacking the Source
    • Installing GNU Make and GCC
      • Installing GNU Make
      • Installing GNU GCC
    • Trying to Compile
    • Compiling With Appropriate Paths
    • Installing The Built Files
    • TL;DR
• Deno Runtime
  • Project Root Absolute Imports and Import Maps in Deno
    • Intro
    • The Problem
    • The Solution
      • Vim
      • VSCode
• How to Design Programs
  • The Book
  • Design Recipes and Examples
  • Racket and BSL
    • Teaching Languages — htdp/bsl 📖
    • Emacs, Geiser
    • Racket Mode
    • Other libs used in the book
    • DrRacket
    • Naming Source Files
  • Images
  • Other Links
  • Other People’s Notes and Solutions
    • Beginning Student Languages
      • Intro
      • List of teaching languages
      • Resources
• Algorithms
  • Big-O of Arrays and Objects
    • Time Complexity
      • Big O of Object Operations
      • Big O of Array Operations
    • Space Complexity
      • Primitive Types
      • Reference Types
    • Code Examples
      • sum() array
        • Unit Tests
        • sum(xs) v1
        • sum(xs) v2
        • sum(xs) v3
      • calcSubtotals(xs)
        • Unit Tests
        • calcSubtotals(xs) v1
  • Space Complexity Examples
    • Sum Array of Numbers
    • Double Array of Numbers
  • Logarithms
  • Problem-Solving
    • Understand The Problem
    • Concrete Examples
      • Frequency Counter Example
    • Break It Down
      • v1
      • v2
    • Solve the problem (or a simplified version of it)
      • charCount() example step by step
        • v1 Simplest Scenario
        • v2 Uppercase and Lowercase
        • v3 Ignore Non-Alphanumeric Chars
        • v4 Refactor Regexp Bit Into Helper Function
  • Helper Functions
    • add(x, y)
    • isEven(n)
  • Split Int Into Even Parts
    • TypeScript
      • Unit Tests
      • v1
      • v2
    • References
• Mostly Adequate Guide to Functional Programming
  • 02 - First Class Functions
    • functions are first-class
    • controller and views
  • 02 Currying
    • Exercise A
    • Exercise B
    • Exercise C
• Composable Functional JavaScript
  • Intro
  • A Note on Extra Examples and Deviations From The Videos
  • A Note on the Wording Used
    • 01 - Create linear data flow with container style types (Box)
      • Intro
      • The Test Suite
      • A Note on the type 1String
      • Temporary Variables
      • Nested Function Invocations
      • Manual Container
      • Manual Container With Helper Functions
      • Container Type
      • nextChar example
    • 02 - Refactor Imperative to Composed Expression using Box
      • Intro
      • Box
        • The Unit Tests
        • Box Implementation
      • moneyToFloat()
        • The Test Suite
        • Imperative Style
        • Functional Style
      • percentToFloat()
        • The Unit Tests
        • Imperative Style
        • Functional Style
      • applyDiscount()
        • The Unit Tests
        • Imperative Style
        • Functional Style
    • 03 - Enforce a null check with composable code branching using Either
      • Intro to Either, Left and Right
      • Left and Right Unit Tests
      • JSDoc Type Definitions
      • Implementation of Left and Right
      • Use of Left and Right
        • The Problem
        • Actually Making Use of Left and Right
        • Improving With fromNullable
        • Final Thoughts
    • 04 - Use chain for composable error handling with nested Eithers
      • v1 - An Initial, Traditional Implementation
      • v2 - Capture Try Catch With Either
      • v3 - Problems With Invalid, Unparsable JSON
      • v4 - tryCatch JSON.parse
      • v5 Using .chain()
      • v6 Final Implementation
        • getPort Unit Tests
        • getPort Implementation
      • Thoughts
    • 05 - A collection of Either examples compared to imperative code
      • openSite()
        • Unit Tests
        • Helper Functions
        • Imperative Style
        • Functional, Composable Style
      • getPrefs()
        • Unit Tests
        • TypeDefs
        • Imperative Style
        • Functional, Composable Style
      • getStreetName()
        • Unit Tests
        • Imperative Style
        • Functional, Composable Style
      • concatUniq()
        • Unit Tests
        • Imperative Style
        • Functional, Composable Style
      • Final Notes
    • Helper Functions
      • log
      • id (identity)
      • isNil
      • fromNullable
      • Either (Left, Right)
        • Either Unit Tests
        • Either Implementation
      • tryCatch
• Codewars Challenges
  • Chicken Scheme
    • Install Necessary Eggs
    • Running Tests
  • TypeScript
    • Running Tests With Deno
    • Unstable APIs
      • 6kyu
        • Find Int That Appears Odd Number of Times
          • Approach 1 (search and count)
          • Approach 2 Bitwise XOR
          • TypeScript
          • Scheme
        • Which Are In
          • Approach 1
          • JavaScript
          • TypeScript
          • Scheme
        • Friend or Foe
          • Approach 1
          • JavaScript
          • TypeScript
          • Scheme
      • 7kyu
        • Sort Numbers
          • TypeScript
          • v1 Sort Function Callback
        • Valid Parentheses
          • Intro
          • Haskell
          • JavaScript
        • Vowel Count
          • Example Input
          • Haskell
          • JavaScript
        • Simple Fun: Diplomas
          • JavaScript
• HackerRank Challenges
  • Problem Solving
    • Diagonal Difference
      • JavaScript
        • Solution 1 with nested loops
        • Solution 2 with single loop
    • Birthday Cake Candles
      • JavaScript
        • Solution 1 with two non-nested loops
        • Solution 2 with single loop and frequency counter
    • Compare The Triplets
      • JavaScript
        • Solution 1
    • Grading Students
      • JavaScript
        • Solution 1
        • Solution 2
    • Plus Minus
      • JavaScript
        • Solution 1 with some helpers
        • Solution 2 frequency counter
    • Sherlock and Array
      • JavaScript
        • Solution 1 with nested loops
        • Solution 2 with accumulators
    • Staircase
      • JavaScript
        • Solution 1
        • Solution 2
    • Strong Password
      • JavaScript
        • Solution 1
        • Solution 2
    • Time Conversion
      • JavaScript
        • Solution 1
        • Solution 2 using ramda and helpers
        • Solution 3 with ramda pipe
    • Camel Case
      • JavaScript
        • Solution 1 with regexp
        • Solution 2 with includes()
        • Solution 3 with regex split
    • Ice Cream Parlor
      • JavaScript
        • Solution 1
        • Solution 2
    • Missing Numbers
      • JavaScript
        • Solution 1
        • Solution 2 with helper
        • Solution 3 with sets, spread, sort and splice
    • Mini Max Sum
      • JavaScript
        • Solution 1
        • Solution 2
  • Easy HackerRank Challenges
    • A Very Big Sum
      • TypeScript
        • Test Cases
        • v1 Procedural for loop
        • v2 FPish with reduce and inline add function
        • v3 FPish with reduce and helper add function
        • Ramda REPL
    • Grading Students
      • Multiples of an integer
      • C
        • Solution 1 :: C
        • Solution 2 :: C
        • Solution 3 :: C
  • Helper Functions
    • add(x, y)
• Programming
  • Unnest Logic From Inside Conditions
    • Introduction
• Docker
  • Bridge Network Examples
    • Intro
    • A custom nginx image with ping utility
    • Default Bridge Networking
    • Pinging by hostname
    • Example using an user-defined bridge network
• Databases and SQL
  • Basics
  • Data Definition Language
  • Data Manipulation Language
    • PSQL CLI :: PostgreSQL
      • Setting the Prompt
      • Visually display null values
      • Visually display empty string
    • Useful PostgreSQL Commands
      • Miscellaneous Commands
      • Roles (users)
      • Creating Databases
      • Backup & Restore
        • Intro Notes
        • From local database
        • From Docker Container
      • Renaming a Database
      • Tables
    • Basic SQL
      • Adults Only
      • Raise to the Power
      • Calculating Batting Average
      • SQL with Pokemon: Damage Multipliers
    • Basic HackerRank SQL Challenges
      • Intro
      • Revising The Select Query I
      • Revising the Select Query II
      • Select All
      • Select By ID
      • Japanese Cities’ Attributes
      • Weather Observation Station 1
      • Weather Observation Station 2
      • Weather Observation Station 3
      • Weather Observation Station 4
      • Weather Observation Station 6
      • Weather Observation Station 5
        • UNION ALL of two queries
        • WHERE IN union of subquery
• Design Patterns
  • Template Method Pattern
    • Use Cases
      • Report Generator
      • Report Generator Ruby Example
      • Email
    • References
  • Strategy Pattern
    • Use Cases
      • Report Generator
        • Ruby
      • Calculating Taxes
    • References
• SOLID Principles
  • Java
    • Running the Examples
      • Open Closed Principle
        • Insurances Example
          • Initial (flawed) Design
          • Improved Design
        • Benefits of OCP
      • Liskov Substitution Principle
        • Birds, Ducks and Ostriches
        • Products
        • Cars
      • Interface Segregation Principle
        • Print and Fax Machines (bad design)
        • Print and Fax Machines (better design)
        • Identifying ISP Violations
      • Dependency Inversion Principle
        • Intro
        • eCommerce Example (bad design)
        • eCommerce Example (better design)
        • Dependency Injection
• Character Encoding
  • Useful Unicode Symbols
    • Ruby
• Software Engineering
  • Links and Resources
• Miscellaneous Tips
  • PlantUML on Sphinx/Read The Docs
    • Motivation
    • Getting Started
    • PlantUML Sphinx Contrib
    • Extensions on conf.py
    • PlantUML package on the container
    • An example diagram
    • Conclusion
  • Paste Image Into Finder
    • The Bash Script
    • Using Quick Actions
    • Add Keyboard Shortcut
    • References