A [WIP] collection of pure bash alternatives to external processes.
The goal of this repository is to document known and unknown methods of doing various tasks using only built-in bash features. Using the snippets from this guide can help to remove unneeded dependencies from your scripts and in most cases make them that little bit faster. I came across these tips and discovered a few while developing [neofetch](https://github.com/dylanaraps/neofetch), [pxltrm](https://github.com/dylanaraps/pxltrm) and some other smaller projects. This repository is open to contribution. If you see something that is incorrectly described, buggy or outright wrong, open an issue or send a pull request. If you know a handy snippet that is not included in this list, send a pull request! **NOTE**: Error handling (*checking if a file exists, etc*) is not included. These are meant to be snippets you can incorporate into your scripts and not full blown utilities. ## Table of Contents * [File handling](#file-handling) * [Get the first N lines of a file.](#get-the-first-n-lines-of-a-file) * [Get the last N lines of a file.](#get-the-last-n-lines-of-a-file) * [Get the number of lines in a file.](#get-the-number-of-lines-in-a-file) * [Strings](#strings) * [Get the directory name of a file path.](#get-the-directory-name-of-a-file-path) * [Trim quotes from a string.](#trim-quotes-from-a-string) * [Arrays](#arrays) * [Reverse an array.](#reverse-an-array) * [Colors](#colors) * [Convert a hex color to RGB.](#convert-a-hex-color-to-rgb) * [Convert an RGB color to hex.](#convert-an-rgb-color-to-hex) * [Miscellaneous](#miscellaneous) * [Getting the terminal size (*in a script*).](#getting-the-terminal-size-in-a-script) * [Get the current date using `strftime`.](#get-the-current-date-using-strftime) ## File handling ### Get the first N lines of a file. Alternative to the `head` command. **NOTE:** Requires `bash` 4+ ```sh head() { # Usage: head "n" "file" mapfile -tn "$1" line < "$2" printf '%s\n' "${line[@]}" } ``` ### Get the last N lines of a file. Alternative to the `tail` command. **NOTE:** Requires `bash` 4+ ```sh tail() { # Usage: tail "n" "file" mapfile -tn 0 line < "$2" printf '%s\n' "${line[@]: -$1}" } ``` ### Get the number of lines in a file. Alternative to `wc -l`. **NOTE:** Requires `bash` 4+ ```sh lines() { # Usage lines "file" mapfile -tn 0 lines < "$1" printf '%s\n' "${#lines[@]}" } ``` ## Strings ### Get the directory name of a file path. Alternative to the `dirname` command. ```sh dirname() { # Usage: dirname "path" printf '%s\n' "${1%/*}/" } ``` ### Trim quotes from a string. ```sh trim_quotes() { # Usage: trim_quotes "string" : "${1//\'}" printf "%s\\n" "${_//\"}" } ``` ## Arrays ### Reverse an array. Enabling `extdebug` allows access to the `BASH_ARGV` array which stores the current function’s arguments in reverse. ```sh reverse_array() { # Usage: reverse_array "array" # reverse_array 1 2 3 4 5 6 shopt -s extdebug f()(printf "%s " "${BASH_ARGV[@]}"); f "$@" shopt -u extdebug printf '\n' } ``` ## Colors ### Convert a hex color to RGB. ```sh hex_to_rgb() { # Usage: hex_to_rgb "#FFFFFF" ((r=16#${1:1:2})) ((g=16#${1:3:2})) ((b=16#${1:5:6})) printf '%s\n' "$r $g $b" } ``` ### Convert an RGB color to hex. ```sh rgb_to_hex() { # Usage: rgb_to_hex "r" "g" "b" printf '#%02x%02x%02x\n' "$1" "$2" "$3" } ``` ## Miscellaneous ### Getting the terminal size (*in a script*). This is handy when writing scripts in pure bash and `stty`/`tput` can’t be called. ```sh get_term_size() { # Usage: get_term_size # (:;:) is a micro sleep to ensure the variables are # exported immediately. shopt -s checkwinsize; (:;:) printf '%s\n' "$LINES $COLUMNS" } ``` ### 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. **NOTE:** Requires `bash` 4+ ```sh date() { # Usage: date "format" # See: 'man strftime' for format. printf "%($1)T\\n" } ```