612 lines
13 KiB
Markdown
612 lines
13 KiB
Markdown
<p align="center"> <img
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src="https://i.imgur.com/1C9VXOg.png"
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height="100px"></p><h3 align="center">pure bash bible</h3> <p align="center">A
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[WIP] collection of pure bash alternatives to external processes.</p>
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------
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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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This repository is open to contribution. If you see something that is
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incorrectly described, buggy or outright wrong, open an issue or send a
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pull request. If you know a handy snippet that is not included in this
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list, send a pull request!
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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 white-space from string.](#trim-white-space-from-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 characters from start of string.](#strip-characters-from-start-of-string)
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* [Strip characters from end of string.](#strip-characters-from-end-of-string)
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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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* [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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* [Iterate over files.](#iterate-over-files)
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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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* [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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* [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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* [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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* [Miscellaneous](#miscellaneous)
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* [Get the current date using `strftime`.](#get-the-current-date-using-strftime)
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* [Bypass shell aliases and functions.](#bypass-shell-aliases-and-functions)
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* [Internal Variables](#internal-variables)
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<!-- vim-markdown-toc -->
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## Strings
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### Trim white-space from string.
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**NOTE**: This also truncates multiple spaces inside the string.
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```sh
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# shellcheck disable=SC2086,SC2048
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trim() {
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# Usage: trim " 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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### Split a string on a delimiter.
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```sh
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# To multiple variables.
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string="1,2,3"
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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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**NOTE:** Requires `bash` 4+
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```sh
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lower() {
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# Usage: lower "string"
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printf '%s\n' "${1,,}"
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}
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```
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### Change a string to uppercase.
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**NOTE:** Requires `bash` 4+
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```sh
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upper() {
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# Usage: upper "string"
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printf '%s\n' "${1^^}"
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}
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```
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### Trim quotes from a string.
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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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### Strip characters from start of string.
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```sh
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lstrip() {
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# Usage: lstrip "string" "chars to remove"
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printf '%s\n' "${1##$2}"
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}
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```
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### Strip characters from end of string.
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```sh
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rstrip() {
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# Usage: rstrip "string" "chars to remove"
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printf '%s\n' "${1%%$2}"
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}
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```
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## Arrays
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### Reverse an array.
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Enabling `extdebug` allows access to the `BASH_ARGV` array which stores
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the current function’s arguments in reverse.
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```sh
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reverse_array() {
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# Usage: reverse_array "array"
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# reverse_array 1 2 3 4 5 6
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shopt -s extdebug
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f()(printf '%s ' "${BASH_ARGV[@]}"); f "$@"
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shopt -u extdebug
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printf '\n'
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}
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```
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### Remove duplicate array elements.
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Create a temporary associative array. When setting associative array
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values and a duplicate assignment occurs, bash overwrites the key. This
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allows us to effectively remove array duplicates.
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**NOTE:** Requires `bash` 4+
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```sh
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remove_array_dups() {
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# Usage: remove_array_dups "array"
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declare -A tmp_array
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for i in "$@"; do
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[[ "$i" ]] && IFS=" " tmp_array["${i:- }"]=1
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done
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printf '%s\n' "${!tmp_array[@]}"
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}
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```
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### Cycle through an array.
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Each time the `printf` is called, the next array element is printed. When
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the print hits the last array element it starts from the first element
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again.
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```sh
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arr=(a b c d)
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printf '%s\n' "${arr[$((i==${#arr[@]}-1?i=0:++i))]}"
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```
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### Toggle between two values.
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This works the same as above, this is just a different use case.
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```sh
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arr=(true false)
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printf '%s\n' "${arr[$((i==${#arr[@]}-1?i=0:++i))]}"
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```
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## File handling
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### Read a file to a string.
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Alternative to the `cat` command.
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```sh
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file_data="$(<"file")"
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```
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### Read a file to an array (*by line*).
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Alternative to the `cat` command.
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```sh
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# Bash <4
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IFS=$'\n' read -d "" -ra file_data < "file"
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# Bash 4+
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mapfile -t file_data < "file"
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```
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### Get the first N lines of a file.
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Alternative to the `head` command.
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**NOTE:** Requires `bash` 4+
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```sh
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head() {
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# Usage: head "n" "file"
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mapfile -tn "$1" line < "$2"
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printf '%s\n' "${line[@]}"
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}
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```
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### Get the last N lines of a file.
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Alternative to the `tail` command.
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**NOTE:** Requires `bash` 4+
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```sh
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tail() {
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# Usage: tail "n" "file"
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mapfile -tn 0 line < "$2"
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printf '%s\n' "${line[@]: -$1}"
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}
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```
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### Get the number of lines in a file.
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Alternative to `wc -l`.
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**NOTE:** Requires `bash` 4+
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```sh
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lines() {
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# Usage lines "file"
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mapfile -tn 0 lines < "$1"
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printf '%s\n' "${#lines[@]}"
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}
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```
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### Iterate over files.
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Don’t use `ls`.
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```sh
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# Greedy example.
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for file in *; do
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printf '%s\n' "$file"
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done
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# PNG files in dir.
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for file in ~/Pictures/*.png; do
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printf '%s\n' "$file"
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done
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# Iterate over directories.
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for dir in ~/Downloads/; do
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printf '%s\n' "$dir"
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done
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# Iterate recursively.
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shopt -s globstar
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for file in ~/Pictures/**/*; do
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printf '%s\n' "$file"
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done
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shopt -u globstar
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```
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### Count files or directories in directory.
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This works by passing the output of the glob as function arguments. We
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then count the arguments and print the number.
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```sh
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count() {
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# Usage: count /path/to/dir/*
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# count /path/to/dir/*/
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printf '%s\n' "$#"
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}
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```
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### Create an empty file.
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Alternative to `touch`.
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```sh
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:> file
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# Longer alternatives:
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echo -n > file
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printf '' > file
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```
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## File Paths
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### Get the directory name of a file path.
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Alternative to the `dirname` command.
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```sh
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dirname() {
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# Usage: dirname "path"
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printf '%s\n' "${1%/*}/"
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}
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```
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### Get the base-name of a file path.
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Alternative to the `basename` command.
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```sh
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basename() {
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# Usage: basename "path"
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: "${1%/}"
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printf '%s\n' "${_##*/}"
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}
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```
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## Arithmetic
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### Simpler syntax to set variables.
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```sh
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# Simple math
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((var=1+2))
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# Decrement/Increment variable
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((var++)
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((var--))
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((var+=1))
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((var-=1))
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# Using variables
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((var=var2*arr[2]))
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```
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### Ternary tests.
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```sh
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# Set the value of var to var2 if var2 is greater than var.
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# var: variable to set.
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# var2>var: Condition to test.
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# ?var2: If the test succeeds.
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# :var: If the test fails.
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((var=var2>var?var2:var))
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```
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## Colors
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### Convert a hex color to RGB.
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```sh
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hex_to_rgb() {
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# Usage: hex_to_rgb "#FFFFFF"
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((r=16#${1:1:2}))
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((g=16#${1:3:2}))
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((b=16#${1:5:6}))
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printf '%s\n' "$r $g $b"
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}
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```
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### Convert an RGB color to hex.
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```sh
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rgb_to_hex() {
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# Usage: rgb_to_hex "r" "g" "b"
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printf '#%02x%02x%02x\n' "$1" "$2" "$3"
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}
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```
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## Information about the terminal
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### Get the terminal size in lines and columns (*from a script*).
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This is handy when writing scripts in pure bash and `stty`/`tput` can’t be
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called.
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```sh
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get_term_size() {
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# Usage: get_term_size
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# (:;:) is a micro sleep to ensure the variables are
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# exported immediately.
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shopt -s checkwinsize; (:;:)
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printf '%s\n' "$LINES $COLUMNS"
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}
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```
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### Get the terminal size in pixels.
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**NOTE**: This does not work in some terminal emulators.
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```sh
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get_window_size() {
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# Usage: get_window_size
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printf '%b' "${TMUX:+\\ePtmux;\\e}\\e[14t${TMUX:+\\e\\\\}"
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IFS=';t' read -d t -t 0.05 -sra term_size
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printf '%s\n' "${term_size[1]}x${term_size[2]}"
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}
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```
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### Get the current cursor position.
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This is useful when creating a TUI in pure bash.
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```sh
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get_cursor_pos() {
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# Usage: get_cursor_pos
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IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
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printf '%s\n' "$x $y"
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}
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```
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## Code Golf
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### Shorter `for` loop syntax.
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```sh
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# Tiny C Style.
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for((;i++<10;)){ echo "$i";}
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# Undocumented method.
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for i in {1..10};{ echo "$i";}
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# Expansion.
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for i in {1..10}; do echo "$i"; done
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# C Style.
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for((i=0;i<=10;i++)); do echo "$i"; done
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```
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### Shorter infinite loops.
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```sh
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# Normal method
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while :; do code; done
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# Shorter
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for((;;)){ code;}
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```
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### Shorter function declaration.
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```sh
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# Normal method
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f(){ echo hi;}
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# Using a subshell
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f()(echo hi)
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# Using arithmetic
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# You can use this to assign integer values.
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# Example: f a=1
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# f a++
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f()(($1))
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# Using tests, loops etc.
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# Note: You can also use ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’.
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f()if true; then echo "$1"; fi
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f()for i in "$@"; do echo "$i"; done
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```
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### Shorter `if` syntax.
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```sh
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# One line
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[[ "$var" == hello ]] && echo hi || echo bye
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[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
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# Multi line (no else, single statement)
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[[ "$var" == hello ]] && \
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echo hi
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# Multi line (no else)
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[[ "$var" == hello ]] && {
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echo hi
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# ...
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}
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```
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### Simpler `case` statement to set variable.
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We can use the `:` builtin to avoid repeating `variable=` in a case
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statement. The `$_` variable stores the last argument of the last
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successful command. `:` always succeeds so we can abuse it to store the
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variable value.
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```sh
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# Example snippet from Neofetch.
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case "$(uname)" in
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"SunOS"): "Solaris" ;;
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"Haiku"): "Haiku" ;;
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"MINIX"): "MINIX" ;;
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"AIX"): "AIX" ;;
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"IRIX"*): "IRIX" ;;
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"FreeMiNT"): "FreeMiNT" ;;
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"Linux" | "GNU"*)
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: "Linux"
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;;
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*"BSD" | "DragonFly" | "Bitrig")
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: "BSD"
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;;
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"CYGWIN"* | "MSYS"* | "MINGW"*)
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: "Windows"
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;;
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*)
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printf '%s\n' "Unknown OS detected: '$kernel_name', aborting..." >&2
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printf '%s\n' "Open an issue on GitHub to add support for your OS." >&2
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exit 1
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;;
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esac
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# Finally, set the variable.
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os="$_"
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```
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## Miscellaneous
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||
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### Get the current date using `strftime`.
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||
|
||
Bash’s `printf` has a built-in method of getting the date which we can use
|
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in place of the `date` command in a lot of cases.
|
||
|
||
**NOTE:** Requires `bash` 4+
|
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|
||
```sh
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date() {
|
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# Usage: date "format"
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# See: 'man strftime' for format.
|
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printf "%($1)T\\n"
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}
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|
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# Examples:
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# Using date.
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date "+%a %d %b - %l:%M %p"
|
||
|
||
# Using printf.
|
||
printf '%(%a %d %b - %l:%M %p)T\n'
|
||
|
||
# Assigning a variable.
|
||
printf -v date '%(%a %d %b - %l:%M %p)T\n'
|
||
```
|
||
|
||
### Bypass shell aliases and functions.
|
||
|
||
```sh
|
||
# alias
|
||
ls
|
||
|
||
# command
|
||
\ls
|
||
```
|
||
|
||
## Internal Variables
|
||
|
||
This will most likely be expanded here. In the meantime, see:
|
||
http://tldp.org/LDP/abs/html/internalvariables.html
|
||
|
||
|