381 lines
8.1 KiB
Markdown
381 lines
8.1 KiB
Markdown
<h1 align="center">pure bash</h1> <p align="center">A [WIP] collection of
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pure bash alternatives to external processes.</p>
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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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## 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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* [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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* [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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* [Miscellaneous](#miscellaneous)
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* [Get the current date using `strftime`.](#get-the-current-date-using-strftime)
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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 "$@"
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shopt -u extdebug
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printf '\n'
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}
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```
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## File handling
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### Read a file to a string.
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Alternative to the `cat` command.
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```sh
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file_data="$(<"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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IFS=$'\n' read -d "" -ra 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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echo "$file"
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done
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# PNG files in dir.
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for file in ~/Pictures/*.png; do
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echo "$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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echo "$dir"
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done
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# Iterate recursively.
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shopt -s globstar
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for file in ~/Pictures/**/*; do
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echo "$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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## 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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## Miscellaneous
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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.
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**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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