1428 lines
27 KiB
Markdown
1428 lines
27 KiB
Markdown
<h1 align="center">pure bash bible</h1> <p
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align="center">A [WIP] collection of pure bash alternatives to external
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processes.</p>
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<p align="center"> <a
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href="https://travis-ci.com/dylanaraps/pure-bash-bible"><img
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src="https://travis-ci.com/dylanaraps/pure-bash-bible.svg?branch=master"></a>
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<a href="./LICENSE.md"><img
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src="https://img.shields.io/badge/license-MIT-blue.svg"></a>
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<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=V7QNJNKS3WYVS"><img src="https://img.shields.io/badge/donate-paypal-green.svg"></a>
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</p>
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<br>
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The goal of this repository is to document known and unknown methods of
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doing various tasks using only built-in bash features. Using the snippets
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from this guide can help to remove unneeded dependencies from your scripts
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and in most cases make them that little bit faster. I came across these
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tips and discovered a few while developing
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[neofetch](https://github.com/dylanaraps/neofetch),
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[pxltrm](https://github.com/dylanaraps/pxltrm) and some other smaller
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projects.
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The snippets below are linted using `shellcheck` and tests have been
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written where applicable. If you're looking to contribute, have a read of
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the
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[CONTRIBUTING.md](https://github.com/dylanaraps/pure-bash-bible/blob/master/CONTRIBUTING.md).
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It outlines how the unit tests work and what's required when adding
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snippets.
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If you see something that is incorrectly described, buggy or outright
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wrong, open an issue or send a pull request. If you know a handy snippet
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that is not included in this list, contribute!
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**NOTE**: Error handling (*checking if a file exists, etc*) is not
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included. These are meant to be snippets you can incorporate into your
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scripts and not full blown utilities.
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<br>
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# Table of Contents
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<!-- vim-markdown-toc GFM -->
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* [Strings](#strings)
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* [Trim leading and trailing white-space from string.](#trim-leading-and-trailing-white-space-from-string)
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* [Trim all white-space from string and truncate spaces.](#trim-all-white-space-from-string-and-truncate-spaces)
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* [Use REGEX on a string.](#use-regex-on-a-string)
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* [Split a string on a delimiter.](#split-a-string-on-a-delimiter)
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* [Change a string to lowercase.](#change-a-string-to-lowercase)
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* [Change a string to uppercase.](#change-a-string-to-uppercase)
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* [Trim quotes from a string.](#trim-quotes-from-a-string)
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* [Strip all instances of pattern from string.](#strip-all-instances-of-pattern-from-string)
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* [Strip first occurrence of pattern from string.](#strip-first-occurrence-of-pattern-from-string)
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* [Strip pattern from start of string.](#strip-pattern-from-start-of-string)
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* [Strip pattern from end of string.](#strip-pattern-from-end-of-string)
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* [Check if string contains a sub-string.](#check-if-string-contains-a-sub-string)
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* [Check if string starts with sub-string.](#check-if-string-starts-with-sub-string)
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* [Check if string ends with sub-string.](#check-if-string-ends-with-sub-string)
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* [Variables](#variables)
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* [Assign and access a variable using a variable.](#assign-and-access-a-variable-using-a-variable)
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* [Arrays](#arrays)
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* [Reverse an array.](#reverse-an-array)
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* [Remove duplicate array elements.](#remove-duplicate-array-elements)
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* [Cycle through an array.](#cycle-through-an-array)
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* [Toggle between two values.](#toggle-between-two-values)
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* [Loops](#loops)
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* [Loop over a range of numbers.](#loop-over-a-range-of-numbers)
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* [Loop over a variable range of numbers.](#loop-over-a-variable-range-of-numbers)
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* [Loop over an array.](#loop-over-an-array)
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* [Loop over an array with an index.](#loop-over-an-array-with-an-index)
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* [Loop over the contents of a file.](#loop-over-the-contents-of-a-file)
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* [Loop over files and directories.](#loop-over-files-and-directories)
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* [File handling](#file-handling)
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* [Read a file to a string.](#read-a-file-to-a-string)
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* [Read a file to an array (*by line*).](#read-a-file-to-an-array-by-line)
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* [Get the first N lines of a file.](#get-the-first-n-lines-of-a-file)
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* [Get the last N lines of a file.](#get-the-last-n-lines-of-a-file)
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* [Get the number of lines in a file.](#get-the-number-of-lines-in-a-file)
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* [Count files or directories in directory.](#count-files-or-directories-in-directory)
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* [Create an empty file.](#create-an-empty-file)
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* [File Paths](#file-paths)
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* [Get the directory name of a file path.](#get-the-directory-name-of-a-file-path)
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* [Get the base-name of a file path.](#get-the-base-name-of-a-file-path)
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* [Arithmetic](#arithmetic)
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* [Simpler syntax to set variables.](#simpler-syntax-to-set-variables)
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* [Ternary tests.](#ternary-tests)
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* [Obsolete Syntax](#obsolete-syntax)
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* [Shebang.](#shebang)
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* [Command Substitution.](#command-substitution)
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* [Function Declaration.](#function-declaration)
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* [Internal Variables](#internal-variables)
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* [Get the location to the `bash` binary.](#get-the-location-to-the-bash-binary)
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* [Get the version of the current running `bash` process.](#get-the-version-of-the-current-running-bash-process)
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* [Open the user's preferred text editor.](#open-the-users-preferred-text-editor)
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* [Get the name of the current function.](#get-the-name-of-the-current-function)
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* [Get the host-name of the system.](#get-the-host-name-of-the-system)
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* [Get the architecture of the Operating System.](#get-the-architecture-of-the-operating-system)
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* [Get the name of the Operating System / Kernel.](#get-the-name-of-the-operating-system--kernel)
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* [Get the current working directory.](#get-the-current-working-directory)
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* [Get the number of seconds the script has been running.](#get-the-number-of-seconds-the-script-has-been-running)
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* [Information about the terminal](#information-about-the-terminal)
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* [Get the terminal size in lines and columns (*from a script*).](#get-the-terminal-size-in-lines-and-columns-from-a-script)
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* [Get the terminal size in pixels.](#get-the-terminal-size-in-pixels)
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* [Get the current cursor position.](#get-the-current-cursor-position)
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* [Colors](#colors)
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* [Convert a hex color to RGB.](#convert-a-hex-color-to-rgb)
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* [Convert an RGB color to hex.](#convert-an-rgb-color-to-hex)
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* [Code Golf](#code-golf)
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* [Shorter `for` loop syntax.](#shorter-for-loop-syntax)
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* [Shorter infinite loops.](#shorter-infinite-loops)
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* [Shorter function declaration.](#shorter-function-declaration)
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* [Shorter `if` syntax.](#shorter-if-syntax)
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* [Simpler `case` statement to set variable.](#simpler-case-statement-to-set-variable)
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* [Other](#other)
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* [Use `read` as an alternative to the `sleep` command.](#use-read-as-an-alternative-to-the-sleep-command)
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* [Check if a program is in the user's PATH.](#check-if-a-program-is-in-the-users-path)
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* [Get the current date using `strftime`.](#get-the-current-date-using-strftime)
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* [Progress bars.](#progress-bars)
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* [Bypass shell aliases.](#bypass-shell-aliases)
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* [Bypass shell functions.](#bypass-shell-functions)
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<!-- vim-markdown-toc -->
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# Strings
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## Trim leading and trailing white-space from string.
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This is an alternative to `sed`, `awk`, `perl` and other tools. The
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function below works by finding all leading and trailing white-space and
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removing it from the start and end of the string. The `:` built-in is used
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in place of a temporary variable.
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**Example Function:**
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```sh
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trim_string() {
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# Usage: trim_string " example string "
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: "${1#"${1%%[![:space:]]*}"}"
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: "${_%"${_##*[![:space:]]}"}"
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printf '%s\n' "$_"
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}
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```
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**Example Usage:**
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```shell
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$ trim_string " Hello, World "
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Hello, World
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$ name=" John Black "
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$ trim_string "$name"
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John Black
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```
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## Trim all white-space from string and truncate spaces.
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This is an alternative to `sed`, `awk`, `perl` and other tools. The
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function below works by abusing word splitting to create a new string
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without leading/trailing white-space and with truncated spaces.
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**Example Function:**
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```sh
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# shellcheck disable=SC2086,SC2048
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trim_all() {
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# Usage: trim_all " example string "
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set -f
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set -- $*
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printf '%s\n' "$*"
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set +f
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}
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```
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**Example Usage:**
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```shell
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$ trim_all " Hello, World "
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Hello, World
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$ name=" John Black is my name. "
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$ trim_all "$name"
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John Black is my name.
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```
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## Use REGEX on a string.
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We can use the result of `bash`'s regex matching to replace `sed` for a
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large number of use-cases.
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**CAVEAT**: This is one of the few platform dependant `bash` features.
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`bash` will use whatever regex engine is installed on the user's system.
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Stick to POSIX regex features if aiming for compatibility.
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**CAVEAT**: This example only prints the first matching group. When using
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multiple capture groups some modification is needed.
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**Example Function:**
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```sh
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regex() {
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# Usage: regex "string" "regex"
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[[ $1 =~ $2 ]] && printf '%s\n' "${BASH_REMATCH[1]}"
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}
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```
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**Example Usage:**
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```shell
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$ # Trim leading white-space.
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$ regex ' hello' '^\s*(.*)'
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hello
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$ # Validate a hex color.
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$ regex "#FFFFFF" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$'
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#FFFFFF
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$ # Validate a hex color (invalid).
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$ regex "red" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$'
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# no output (invalid)
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```
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**Example Usage in script:**
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```shell
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is_hex_color() {
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if [[ "$1" =~ ^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$ ]]; then
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printf '%s\n' "${BASH_REMATCH[1]}"
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else
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printf '%s\n' "error: $1 is an invalid color."
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return 1
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fi
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}
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read -r color
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is_hex_color "$color" || color="#FFFFFF"
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# Do stuff.
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```
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## Split a string on a delimiter.
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This is an alternative to `cut`, `awk` and other tools.
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```shell
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string="1,2,3"
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# To multiple variables.
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IFS=, read -r var1 var2 var3 <<< "$string"
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# To an array.
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IFS=, read -ra vars <<< "$string"
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```
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## Change a string to lowercase.
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**CAVEAT:** Requires `bash` 4+
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**Example Function:**
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```sh
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lower() {
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# Usage: lower "string"
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printf '%s\n' "${1,,}"
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}
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```
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**Example Usage:**
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```shell
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$ lower "HELLO"
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hello
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$ lower "HeLlO"
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hello
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$ lower "hello"
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hello
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```
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## Change a string to uppercase.
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**CAVEAT:** Requires `bash` 4+
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**Example Function:**
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```sh
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upper() {
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# Usage: upper "string"
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printf '%s\n' "${1^^}"
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}
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```
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**Example Usage:**
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```shell
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$ upper "hello"
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HELLO
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$ upper "HeLlO"
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HELLO
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$ upper "HELLO"
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HELLO
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```
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## Trim quotes from a string.
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**Example Function:**
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```sh
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trim_quotes() {
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# Usage: trim_quotes "string"
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: "${1//\'}"
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printf "%s\\n" "${_//\"}"
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}
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```
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**Example Usage:**
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```shell
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$ var="'Hello', \"World\""
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$ trim_quotes "$var"
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Hello, World
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```
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## Strip all instances of pattern from string.
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**Example Function:**
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```sh
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strip_all() {
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# Usage: strip_all "string" "pattern"
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printf '%s\n' "${1//$2}"
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}
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```
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**Example Usage:**
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```shell
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$ strip_all "The Quick Brown Fox" "[aeiou]"
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Th Qck Brwn Fx
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$ strip_all "The Quick Brown Fox" "[[:space:]]"
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TheQuickBrownFox
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$ strip_all "The Quick Brown Fox" "Quick "
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The Brown Fox
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```
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## Strip first occurrence of pattern from string.
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**Example Function:**
|
||
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```sh
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strip() {
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# Usage: strip "string" "pattern"
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printf '%s\n' "${1/$2}"
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}
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```
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**Example Usage:**
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```shell
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$ strip "The Quick Brown Fox" "[aeiou]"
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Th Quick Brown Fox
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$ strip "The Quick Brown Fox" "[[:space:]]"
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TheQuick Brown Fox
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```
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## Strip pattern from start of string.
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**Example Function:**
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||
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```sh
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lstrip() {
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# Usage: lstrip "string" "pattern"
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printf '%s\n' "${1##$2}"
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}
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```
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**Example Usage:**
|
||
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```shell
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$ lstrip "The Quick Brown Fox" "The "
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Quick Brown Fox
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```
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## Strip pattern from end of string.
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|
||
**Example Function:**
|
||
|
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```sh
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rstrip() {
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# Usage: rstrip "string" "pattern"
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printf '%s\n' "${1%%$2}"
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}
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```
|
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**Example Usage:**
|
||
|
||
```shell
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$ rstrip "The Quick Brown Fox" " Fox"
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The Quick Brown
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```
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|
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## Check if string contains a sub-string.
|
||
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**Using a test:**
|
||
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```shell
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if [[ "$var" == *sub_string* ]]; then
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printf '%s\n' "sub_string is in var."
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fi
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|
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# Inverse (substring not in string).
|
||
if [[ "$var" != *sub_string* ]]; then
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printf '%s\n' "sub_string is not in var."
|
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fi
|
||
|
||
# This works for arrays too!
|
||
if [[ "${arr[*]}" == *sub_string* ]]; then
|
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printf '%s\n' "sub_string is in array."
|
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fi
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```
|
||
|
||
## Check if string starts with sub-string.
|
||
|
||
```shell
|
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if [[ "$var" == sub_string* ]]; then
|
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printf '%s\n' "var starts with sub_string."
|
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fi
|
||
|
||
# Inverse (var doesn't start with sub_string).
|
||
if [[ "$var" != sub_string* ]]; then
|
||
printf '%s\n' "var does not start with sub_string."
|
||
fi
|
||
```
|
||
|
||
## Check if string ends with sub-string.
|
||
|
||
```shell
|
||
if [[ "$var" == *sub_string ]]; then
|
||
printf '%s\n' "var ends with sub_string."
|
||
fi
|
||
|
||
# Inverse (var doesn't start with sub_string).
|
||
if [[ "$var" != *sub_string ]]; then
|
||
printf '%s\n' "var does not end with sub_string."
|
||
fi
|
||
```
|
||
|
||
**Using a case statement:**
|
||
|
||
```shell
|
||
case "$var" in
|
||
*sub_string*)
|
||
# Do stuff
|
||
;;
|
||
|
||
*sub_string2*)
|
||
# Do more stuff
|
||
;;
|
||
|
||
*)
|
||
# Else
|
||
;;
|
||
esac
|
||
```
|
||
|
||
# Variables
|
||
|
||
## Assign and access a variable using a variable.
|
||
|
||
```shell
|
||
hello_world="test"
|
||
|
||
# Create the variable name.
|
||
var1="world"
|
||
var2="hello_${var1}"
|
||
|
||
# Print the value of the variable name stored in 'hello_$var1'.
|
||
printf '%s\n' "${!var2}"
|
||
```
|
||
|
||
|
||
# Arrays
|
||
|
||
## Reverse an array.
|
||
|
||
Enabling `extdebug` allows access to the `BASH_ARGV` array which stores
|
||
the current function’s arguments in reverse.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
reverse_array() {
|
||
# Usage: reverse_array "array"
|
||
shopt -s extdebug
|
||
f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@"
|
||
shopt -u extdebug
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ reverse_array 1 2 3 4 5
|
||
5
|
||
4
|
||
3
|
||
2
|
||
1
|
||
|
||
$ arr=(red blue green)
|
||
$ reverse_array "${arr[@]}"
|
||
green
|
||
blue
|
||
red
|
||
```
|
||
|
||
## Remove duplicate array elements.
|
||
|
||
Create a temporary associative array. When setting associative array
|
||
values and a duplicate assignment occurs, bash overwrites the key. This
|
||
allows us to effectively remove array duplicates.
|
||
|
||
**CAVEAT:** Requires `bash` 4+
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
remove_array_dups() {
|
||
# Usage: remove_array_dups "array"
|
||
declare -A tmp_array
|
||
|
||
for i in "$@"; do
|
||
[[ "$i" ]] && IFS=" " tmp_array["${i:- }"]=1
|
||
done
|
||
|
||
printf '%s\n' "${!tmp_array[@]}"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ remove_array_dups 1 1 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5
|
||
1
|
||
2
|
||
3
|
||
4
|
||
5
|
||
|
||
$ arr=(red red green blue blue)
|
||
$ remove_array_dups "${arr[@]}"
|
||
red
|
||
green
|
||
blue
|
||
```
|
||
|
||
## Cycle through an array.
|
||
|
||
Each time the `printf` is called, the next array element is printed. When
|
||
the print hits the last array element it starts from the first element
|
||
again.
|
||
|
||
```sh
|
||
arr=(a b c d)
|
||
|
||
cycle() {
|
||
printf '%s ' "${arr[${i:=0}]}"
|
||
((i=i>=${#arr[@]}-1?0:++i))
|
||
}
|
||
```
|
||
|
||
|
||
## Toggle between two values.
|
||
|
||
This works the same as above, this is just a different use case.
|
||
|
||
```sh
|
||
arr=(true false)
|
||
|
||
cycle() {
|
||
printf '%s ' "${arr[${i:=0}]}"
|
||
((i=i>=${#arr[@]}-1?0:++i))
|
||
}
|
||
```
|
||
|
||
# Loops
|
||
|
||
## Loop over a range of numbers.
|
||
|
||
Don't use `seq`.
|
||
|
||
```shell
|
||
# Loop from 0-100 (no variable support).
|
||
for i in {0..100}; do
|
||
printf '%s\n' "$i"
|
||
done
|
||
```
|
||
|
||
## Loop over a variable range of numbers.
|
||
|
||
Don't use `seq`.
|
||
|
||
```shell
|
||
# Loop from 0-VAR.
|
||
VAR=50
|
||
for ((i=0;i<=VAR;i++)); do
|
||
printf '%s\n' "$i"
|
||
done
|
||
```
|
||
|
||
## Loop over an array.
|
||
|
||
```shell
|
||
arr=(apples oranges tomatoes)
|
||
|
||
# Just elements.
|
||
for element in "${arr[@]}"; do
|
||
printf '%s\n' "$element"
|
||
done
|
||
```
|
||
|
||
## Loop over an array with an index.
|
||
|
||
```shell
|
||
arr=(apples oranges tomatoes)
|
||
|
||
# Elements and index.
|
||
for i in "${!arr[@]}"; do
|
||
printf '%s\n' "${arr[$i]}"
|
||
done
|
||
|
||
# Alternative method.
|
||
for ((i=0;i<${#arr[@]};i++)); do
|
||
printf '%s\n' "${arr[$i]}"
|
||
done
|
||
```
|
||
|
||
## Loop over the contents of a file.
|
||
|
||
```shell
|
||
while read -r line; do
|
||
printf '%s\n' "$line"
|
||
done < "file"
|
||
```
|
||
|
||
## Loop over files and directories.
|
||
|
||
Don’t use `ls`.
|
||
|
||
```shell
|
||
# Greedy example.
|
||
for file in *; do
|
||
printf '%s\n' "$file"
|
||
done
|
||
|
||
# PNG files in dir.
|
||
for file in ~/Pictures/*.png; do
|
||
printf '%s\n' "$file"
|
||
done
|
||
|
||
# Iterate over directories.
|
||
for dir in ~/Downloads/*/; do
|
||
printf '%s\n' "$dir"
|
||
done
|
||
|
||
# Iterate recursively.
|
||
shopt -s globstar
|
||
for file in ~/Pictures/**/*; do
|
||
printf '%s\n' "$file"
|
||
done
|
||
shopt -u globstar
|
||
```
|
||
|
||
|
||
# File handling
|
||
|
||
## Read a file to a string.
|
||
|
||
Alternative to the `cat` command.
|
||
|
||
```shell
|
||
file_data="$(<"file")"
|
||
```
|
||
|
||
## Read a file to an array (*by line*).
|
||
|
||
Alternative to the `cat` command.
|
||
|
||
```shell
|
||
# Bash <4
|
||
IFS=$'\n' read -d "" -ra file_data < "file"
|
||
|
||
# Bash 4+
|
||
mapfile -t file_data < "file"
|
||
```
|
||
|
||
## Get the first N lines of a file.
|
||
|
||
Alternative to the `head` command.
|
||
|
||
**CAVEAT:** Requires `bash` 4+
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
head() {
|
||
# Usage: head "n" "file"
|
||
mapfile -tn "$1" line < "$2"
|
||
printf '%s\n' "${line[@]}"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ head 2 ~/.bashrc
|
||
# Prompt
|
||
PS1='➜ '
|
||
|
||
$ head 1 ~/.bashrc
|
||
# Prompt
|
||
```
|
||
|
||
## Get the last N lines of a file.
|
||
|
||
Alternative to the `tail` command.
|
||
|
||
**CAVEAT:** Requires `bash` 4+
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
tail() {
|
||
# Usage: tail "n" "file"
|
||
mapfile -tn 0 line < "$2"
|
||
printf '%s\n' "${line[@]: -$1}"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ tail 2 ~/.bashrc
|
||
# Enable tmux.
|
||
# [[ -z "$TMUX" ]] && exec tmux
|
||
|
||
$ tail 1 ~/.bashrc
|
||
# [[ -z "$TMUX" ]] && exec tmux
|
||
```
|
||
|
||
## Get the number of lines in a file.
|
||
|
||
Alternative to `wc -l`.
|
||
|
||
**Example Function (bash 4):**
|
||
|
||
```sh
|
||
lines() {
|
||
# Usage: lines "file"
|
||
mapfile -tn 0 lines < "$1"
|
||
printf '%s\n' "${#lines[@]}"
|
||
}
|
||
```
|
||
|
||
**Example Function (bash 3):**
|
||
|
||
This method uses less memory than the `mapfile` method and it's more
|
||
compatible but it's slower for bigger files.
|
||
|
||
```sh
|
||
lines_loop() {
|
||
# Usage: lines_loop "file"
|
||
count=0
|
||
while IFS= read -r _; do
|
||
((count++))
|
||
done < "$1"
|
||
printf '%s\n' "$count"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ lines ~/.bashrc
|
||
48
|
||
|
||
$ lines_loop ~/.bashrc
|
||
48
|
||
```
|
||
|
||
## Count files or directories in directory.
|
||
|
||
This works by passing the output of the glob as function arguments. We
|
||
then count the arguments and print the number.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
count() {
|
||
# Usage: count /path/to/dir/*
|
||
# count /path/to/dir/*/
|
||
printf '%s\n' "$#"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
# Count all files in dir.
|
||
$ count ~/Downloads/*
|
||
232
|
||
|
||
# Count all dirs in dir.
|
||
$ count ~/Downloads/*/
|
||
45
|
||
|
||
# Count all jpg files in dir.
|
||
$ count ~/Pictures/*.jpg
|
||
64
|
||
```
|
||
|
||
## Create an empty file.
|
||
|
||
Alternative to `touch`.
|
||
|
||
```shell
|
||
# Shortest.
|
||
:> file
|
||
|
||
# Longer alternatives:
|
||
echo -n > file
|
||
printf '' > file
|
||
```
|
||
|
||
# File Paths
|
||
|
||
## Get the directory name of a file path.
|
||
|
||
Alternative to the `dirname` command.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
dirname() {
|
||
# Usage: dirname "path"
|
||
printf '%s\n' "${1%/*}/"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ dirname ~/Pictures/Wallpapers/1.jpg
|
||
/home/black/Pictures/Wallpapers/
|
||
|
||
$ dirname ~/Pictures/Downloads/
|
||
/home/black/Pictures/
|
||
```
|
||
|
||
## Get the base-name of a file path.
|
||
|
||
Alternative to the `basename` command.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
basename() {
|
||
# Usage: basename "path"
|
||
: "${1%/}"
|
||
printf '%s\n' "${_##*/}"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ basename ~/Pictures/Wallpapers/1.jpg
|
||
1.jpg
|
||
|
||
$ basename ~/Pictures/Downloads/
|
||
Downloads
|
||
```
|
||
|
||
|
||
# Arithmetic
|
||
|
||
## Simpler syntax to set variables.
|
||
|
||
```shell
|
||
# Simple math
|
||
((var=1+2))
|
||
|
||
# Decrement/Increment variable
|
||
((var++))
|
||
((var--))
|
||
((var+=1))
|
||
((var-=1))
|
||
|
||
# Using variables
|
||
((var=var2*arr[2]))
|
||
```
|
||
|
||
## Ternary tests.
|
||
|
||
```shell
|
||
# Set the value of var to var2 if var2 is greater than var.
|
||
# var: variable to set.
|
||
# var2>var: Condition to test.
|
||
# ?var2: If the test succeeds.
|
||
# :var: If the test fails.
|
||
((var=var2>var?var2:var))
|
||
```
|
||
|
||
# Obsolete Syntax
|
||
|
||
## Shebang.
|
||
|
||
Use `#!/usr/bin/env bash` instead of `#!/bin/bash`.
|
||
|
||
- The former searches the user's `PATH` to find the `bash` binary.
|
||
- The latter assumes it is always installed to `/bin/` which can cause issues.
|
||
|
||
```shell
|
||
# Right:
|
||
|
||
#!/usr/bin/env bash
|
||
|
||
# Wrong:
|
||
|
||
#!/bin/bash
|
||
```
|
||
|
||
## Command Substitution.
|
||
|
||
Use `$()` instead of `` ` ` ``.
|
||
|
||
```shell
|
||
# Right.
|
||
var="$(command)"
|
||
|
||
# Wrong.
|
||
var=`command`
|
||
|
||
# $() can easily be nested whereas `` cannot.
|
||
var="$(command "$(command)")"
|
||
```
|
||
|
||
## Function Declaration.
|
||
|
||
Don't use the `function` keyword, it reduces compatibility with older versions of `bash`.
|
||
|
||
```shell
|
||
# Right.
|
||
do_something() {
|
||
# ...
|
||
}
|
||
|
||
# Wrong.
|
||
function do_something() {
|
||
# ...
|
||
}
|
||
```
|
||
|
||
|
||
# Internal Variables
|
||
|
||
**NOTE**: This list does not include every internal variable (*You can
|
||
help by adding a missing entry!*).
|
||
|
||
For a complete list, see:
|
||
http://tldp.org/LDP/abs/html/internalvariables.html
|
||
|
||
## Get the location to the `bash` binary.
|
||
|
||
```shell
|
||
"$BASH"
|
||
```
|
||
|
||
## Get the version of the current running `bash` process.
|
||
|
||
```shell
|
||
# As a string.
|
||
"$BASH_VERSION"
|
||
|
||
# As an array.
|
||
"${BASH_VERSINFO[@]}"
|
||
```
|
||
|
||
## Open the user's preferred text editor.
|
||
|
||
```shell
|
||
"$EDITOR" "$file"
|
||
|
||
# NOTE: This variable may be empty, set a fallback value.
|
||
"${EDITOR:-vi}" "$file"
|
||
```
|
||
|
||
## Get the name of the current function.
|
||
|
||
```shell
|
||
# Current function.
|
||
"${FUNCNAME[0]}"
|
||
|
||
# Parent function.
|
||
"${FUNCNAME[1]}"
|
||
|
||
# So on and so forth.
|
||
"${FUNCNAME[2]}"
|
||
"${FUNCNAME[3]}"
|
||
|
||
# All functions including parents.
|
||
"${FUNCNAME[@]}"
|
||
```
|
||
|
||
## Get the host-name of the system.
|
||
|
||
```shell
|
||
"$HOSTNAME"
|
||
|
||
# NOTE: This variable may be empty.
|
||
# Optionally set a fallback to the hostname command.
|
||
"${HOSTNAME:-$(hostname)}"
|
||
```
|
||
|
||
## Get the architecture of the Operating System.
|
||
|
||
```shell
|
||
"$HOSTTYPE"
|
||
```
|
||
|
||
## Get the name of the Operating System / Kernel.
|
||
|
||
This can be used to add conditional support for different Operating
|
||
Systems without needing to call `uname`.
|
||
|
||
```shell
|
||
"$OSTYPE"
|
||
```
|
||
|
||
## Get the current working directory.
|
||
|
||
This is an alternative to the `pwd` built-in.
|
||
|
||
```shell
|
||
"$PWD"
|
||
```
|
||
|
||
## Get the number of seconds the script has been running.
|
||
|
||
```shell
|
||
"$SECONDS"
|
||
```
|
||
|
||
# Information about the terminal
|
||
|
||
## Get the terminal size in lines and columns (*from a script*).
|
||
|
||
This is handy when writing scripts in pure bash and `stty`/`tput` can’t be
|
||
called.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
get_term_size() {
|
||
# Usage: get_term_size
|
||
|
||
# (:;:) is a micro sleep to ensure the variables are
|
||
# exported immediately.
|
||
shopt -s checkwinsize; (:;:)
|
||
printf '%s\n' "$LINES $COLUMNS"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
# Output: LINES COLUMNS
|
||
$ get_term_size
|
||
15 55
|
||
```
|
||
|
||
## Get the terminal size in pixels.
|
||
|
||
**CAVEAT**: This does not work in some terminal emulators.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
get_window_size() {
|
||
# Usage: get_window_size
|
||
printf '%b' "${TMUX:+\\ePtmux;\\e}\\e[14t${TMUX:+\\e\\\\}"
|
||
IFS=';t' read -d t -t 0.05 -sra term_size
|
||
printf '%s\n' "${term_size[1]}x${term_size[2]}"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
# Output: WIDTHxHEIGHT
|
||
$ get_window_size
|
||
1200x800
|
||
|
||
# Output (fail):
|
||
$ get_window_size
|
||
x
|
||
```
|
||
|
||
|
||
## Get the current cursor position.
|
||
|
||
This is useful when creating a TUI in pure bash.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
get_cursor_pos() {
|
||
# Usage: get_cursor_pos
|
||
IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
|
||
printf '%s\n' "$x $y"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
# Output: X Y
|
||
$ get_cursor_pos
|
||
1 8
|
||
```
|
||
|
||
# Colors
|
||
|
||
## Convert a hex color to RGB.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
hex_to_rgb() {
|
||
# Usage: hex_to_rgb "#FFFFFF"
|
||
((r=16#${1:1:2}))
|
||
((g=16#${1:3:2}))
|
||
((b=16#${1:5:6}))
|
||
|
||
printf '%s\n' "$r $g $b"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ hex_to_rgb "#FFFFFF"
|
||
255 255 255
|
||
```
|
||
|
||
|
||
## Convert an RGB color to hex.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
rgb_to_hex() {
|
||
# Usage: rgb_to_hex "r" "g" "b"
|
||
printf '#%02x%02x%02x\n' "$1" "$2" "$3"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
$ rgb_to_hex "255" "255" "255"
|
||
#FFFFFF
|
||
```
|
||
|
||
|
||
# Code Golf
|
||
|
||
## Shorter `for` loop syntax.
|
||
|
||
```shell
|
||
# Tiny C Style.
|
||
for((;i++<10;)){ echo "$i";}
|
||
|
||
# Undocumented method.
|
||
for i in {1..10};{ echo "$i";}
|
||
|
||
# Expansion.
|
||
for i in {1..10}; do echo "$i"; done
|
||
|
||
# C Style.
|
||
for((i=0;i<=10;i++)); do echo "$i"; done
|
||
```
|
||
|
||
## Shorter infinite loops.
|
||
|
||
```shell
|
||
# Normal method
|
||
while :; do echo hi; done
|
||
|
||
# Shorter
|
||
for((;;)){ echo hi;}
|
||
```
|
||
|
||
## Shorter function declaration.
|
||
|
||
```shell
|
||
# Normal method
|
||
f(){ echo hi;}
|
||
|
||
# Using a subshell
|
||
f()(echo hi)
|
||
|
||
# Using arithmetic
|
||
# You can use this to assign integer values.
|
||
# Example: f a=1
|
||
# f a++
|
||
f()(($1))
|
||
|
||
# Using tests, loops etc.
|
||
# NOTE: You can also use ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’.
|
||
f()if true; then echo "$1"; fi
|
||
f()for i in "$@"; do echo "$i"; done
|
||
```
|
||
|
||
## Shorter `if` syntax.
|
||
|
||
```shell
|
||
# One line
|
||
# Note: The 3rd statement may run when the 1st is true
|
||
[[ "$var" == hello ]] && echo hi || echo bye
|
||
[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
|
||
|
||
# Multi line (no else, single statement)
|
||
# Note: The exit status may not be the same as with an if statement
|
||
[[ "$var" == hello ]] && \
|
||
echo hi
|
||
|
||
# Multi line (no else)
|
||
[[ "$var" == hello ]] && {
|
||
echo hi
|
||
# ...
|
||
}
|
||
```
|
||
|
||
## Simpler `case` statement to set variable.
|
||
|
||
We can use the `:` builtin to avoid repeating `variable=` in a case
|
||
statement. The `$_` variable stores the last argument of the last
|
||
successful command. `:` always succeeds so we can abuse it to store the
|
||
variable value.
|
||
|
||
```shell
|
||
# Example snippet from Neofetch.
|
||
case "$(uname)" in
|
||
"Linux" | "GNU"*)
|
||
: "Linux"
|
||
;;
|
||
|
||
*"BSD" | "DragonFly" | "Bitrig")
|
||
: "BSD"
|
||
;;
|
||
|
||
"CYGWIN"* | "MSYS"* | "MINGW"*)
|
||
: "Windows"
|
||
;;
|
||
|
||
*)
|
||
printf '%s\n' "Unknown OS detected, aborting..." >&2
|
||
exit 1
|
||
;;
|
||
esac
|
||
|
||
# Finally, set the variable.
|
||
os="$_"
|
||
```
|
||
|
||
# Other
|
||
|
||
## Use `read` as an alternative to the `sleep` command.
|
||
|
||
I was surprised to find out `sleep` is an external command and isn't a
|
||
built-in.
|
||
|
||
**Example Funcrion:**
|
||
|
||
```sh
|
||
read_sleep() {
|
||
# Usage: sleep 1
|
||
# sleep 0.2
|
||
read -rst "${1:-1}" -N 999
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
read_sleep 1
|
||
read_sleep 0.1
|
||
read_sleep 30
|
||
```
|
||
|
||
## Check if a program is in the user's PATH.
|
||
|
||
```shell
|
||
# There are 3 ways to do this and you can use either of
|
||
# these in the same way.
|
||
type -p executable_name &>/dev/null
|
||
hash executable_name &>/dev/null
|
||
command -v executable_name &>/dev/null
|
||
|
||
# As a test.
|
||
if type -p executable_name &>/dev/null; then
|
||
# Program is in PATH.
|
||
fi
|
||
|
||
# Inverse.
|
||
if ! type -p executable_name &>/dev/null; then
|
||
# Program is not in PATH.
|
||
fi
|
||
|
||
# Example (Exit early if program isn't installed).
|
||
if ! type -p convert &>/dev/null; then
|
||
printf '%s\n' "error: convert isn't installed, exiting..."
|
||
exit 1
|
||
fi
|
||
```
|
||
|
||
## Get the current date using `strftime`.
|
||
|
||
Bash’s `printf` has a built-in method of getting the date which we can use
|
||
in place of the `date` command in a lot of cases.
|
||
|
||
**CAVEAT:** Requires `bash` 4+
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
date() {
|
||
# Usage: date "format"
|
||
# See: 'man strftime' for format.
|
||
printf "%($1)T\\n" "-1"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
# Using above function.
|
||
$ date "%a %d %b - %l:%M %p"
|
||
Fri 15 Jun - 10:00 AM
|
||
|
||
# Using printf directly.
|
||
$ printf '%(%a %d %b - %l:%M %p)T\n' "-1"
|
||
Fri 15 Jun - 10:00 AM
|
||
|
||
# Assigning a variable using printf.
|
||
$ printf -v date '%(%a %d %b - %l:%M %p)T\n' '-1'
|
||
$ printf '%s\n' "$date"
|
||
Fri 15 Jun - 10:00 AM
|
||
```
|
||
|
||
## Progress bars.
|
||
|
||
This is a simple way of drawing progress bars without needing a for loop
|
||
in the function itself.
|
||
|
||
**Example Function:**
|
||
|
||
```sh
|
||
bar() {
|
||
# Usage: bar 1 10
|
||
# ^----- Elapsed Percentage (0-100).
|
||
# ^-- Total length in chars.
|
||
((elapsed=$1*$2/100))
|
||
|
||
# Create the bar with spaces.
|
||
printf -v prog "%${elapsed}s"
|
||
printf -v total "%$(($2-elapsed))s"
|
||
|
||
printf '%s\r' "[${prog// /-}${total}]"
|
||
}
|
||
```
|
||
|
||
**Example Usage:**
|
||
|
||
```shell
|
||
for ((i=0;i<=100;i++)); do
|
||
# Pure bash micro sleeps (for the example).
|
||
(:;:) && (:;:) && (:;:) && (:;:) && (:;:)
|
||
|
||
# Print the bar.
|
||
bar "$i" "10"
|
||
done
|
||
|
||
printf '\n'
|
||
```
|
||
|
||
|
||
## Bypass shell aliases.
|
||
|
||
```shell
|
||
# alias
|
||
ls
|
||
|
||
# command
|
||
# shellcheck disable=SC1001
|
||
\ls
|
||
```
|
||
|
||
## Bypass shell functions.
|
||
|
||
```shell
|
||
# function
|
||
ls
|
||
|
||
# command
|
||
command ls
|
||
```
|