The goal of this book is to document commonly-known and lesser-known methods of doing various tasks using only built-in bash features. Using the snippets from this bible can help remove unneeded dependencies from scripts and in most cases make them faster. I came across these tips and discovered a few while developing neofetch, pxltrm and other smaller projects.

The snippets below are linted using shellcheck and tests have been written where applicable. Want to contribute? Read the CONTRIBUTING.md. It outlines how the unit tests work and what is required when adding snippets to the bible.

See something incorrectly described, buggy or outright wrong? Open an issue or send a pull request. If the bible is missing something, open an issue and a solution will be found.

Table of Contents

• FOREWORD
• STRINGS
  • Trim leading and trailing white-space from string
  • Trim all white-space from string and truncate spaces
  • Use regex on a string
  • Split a string on a delimiter
  • Change a string to lowercase
  • Change a string to uppercase
  • Reverse a string case
  • Trim quotes from a string
  • Strip all instances of pattern from string
  • Strip first occurrence of pattern from string
  • Strip pattern from start of string
  • Strip pattern from end of string
  • Percent-encode a string
  • Decode a percent-encoded string
  • Check if string contains a sub-string
  • Check if string starts with sub-string
  • Check if string ends with sub-string
• ARRAYS
  • Reverse an array
  • Remove duplicate array elements
  • Random array element
  • Cycle through an array
  • Toggle between two values
• LOOPS
  • Loop over a range of numbers
  • Loop over a variable range of numbers
  • Loop over an array
  • Loop over an array with an index
  • Loop over the contents of a file
  • Loop over files and directories
• FILE HANDLING
  • Read a file to a string
  • Read a file to an array (by line)
  • Get the first N lines of a file
  • Get the last N lines of a file
  • Get the number of lines in a file
  • Count files or directories in directory
  • Create an empty file
  • Extract lines between two markers
• FILE PATHS
  • Get the directory name of a file path
  • Get the base-name of a file path
• VARIABLES
  • Assign and access a variable using a variable
  • Name a variable based on another variable
• ESCAPE SEQUENCES
  • Text Colors
  • Text Attributes
  • Cursor Movement
  • Erasing Text
• PARAMETER EXPANSION
  • Indirection
  • Replacement
  • Length
  • Expansion
  • Case Modification
  • Default Value
• BRACE EXPANSION
  • Ranges
  • String Lists
• CONDITIONAL EXPRESSIONS
  • File Conditionals
  • File Comparisons
  • Variable Conditionals
  • Variable Comparisons
• ARITHMETIC OPERATORS
  • Assignment
  • Arithmetic
  • Bitwise
  • Logical
  • Miscellaneous
• ARITHMETIC
  • Simpler syntax to set variables
  • Ternary Tests
• TRAPS
  • Do something on script exit
  • Ignore terminal interrupt (CTRL+C, SIGINT)
  • React to window resize
  • Do something before every command
  • Do something when a shell function or a sourced file finishes executing
• PERFORMANCE
  • Disable Unicode
• OBSOLETE SYNTAX
  • Shebang
  • Command Substitution
  • Function Declaration
• INTERNAL VARIABLES
  • Get the location to the bash binary
  • Get the version of the current running bash process
  • Open the user's preferred text editor
  • Get the name of the current function
  • Get the host-name of the system
  • Get the architecture of the Operating System
  • Get the name of the Operating System / Kernel
  • Get the current working directory
  • Get the number of seconds the script has been running
  • Get a pseudorandom integer
• INFORMATION ABOUT THE TERMINAL
  • Get the terminal size in lines and columns (from a script)
  • Get the terminal size in pixels
  • Get the current cursor position
• CONVERSION
  • Convert a hex color to RGB
  • Convert an RGB color to hex
• CODE GOLF
  • Shorter for loop syntax
  • Shorter infinite loops
  • Shorter function declaration
  • Shorter if syntax
  • Simpler case statement to set variable
• OTHER
  • Use read as an alternative to the sleep command
  • Check if a program is in the user's PATH
  • Get the current date using strftime
  • Get the username of the current user
  • Generate a UUID V4
  • Progress bars
  • Get the list of functions in a script
  • Bypass shell aliases
  • Bypass shell functions
  • Run a command in the background
  • Capture function return without command substitution
• AFTERWORD

FOREWORD

A collection of pure bash alternatives to external processes and programs. The bash scripting language is more powerful than people realise and most tasks can be accomplished without depending on external programs.

Calling an external process in bash is expensive and excessive use will cause a noticeable slowdown. Scripts and programs written using built-in methods (where applicable) will be faster, require fewer dependencies and afford a better understanding of the language itself.

The contents of this book provide a reference for solving problems encountered when writing programs and scripts in bash. Examples are in function formats showcasing how to incorporate these solutions into code.

STRINGS

Trim leading and trailing white-space from string

This is an alternative to sed, awk, perl and other tools. The function below works by finding all leading and trailing white-space and removing it from the start and end of the string. The : built-in is used in place of a temporary variable.

Example Function:

trim_string() {
    # Usage: trim_string "   example   string    "
    : "${1#"${1%%[![:space:]]*}"}"
    : "${_%"${_##*[![:space:]]}"}"
    printf '%s\n' "$_"
}

Example Usage:

$ trim_string "    Hello,  World    "
Hello,  World

$ name="   John Black  "
$ trim_string "$name"
John Black

Trim all white-space from string and truncate spaces

This is an alternative to sed, awk, perl and other tools. The function below works by abusing word splitting to create a new string without leading/trailing white-space and with truncated spaces.

Example Function:

# shellcheck disable=SC2086,SC2048
trim_all() {
    # Usage: trim_all "   example   string    "
    set -f
    set