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 * [Strings](#strings) * [Trim white-space from string.](#trim-white-space-from-string) * [Split a string on a delimiter.](#split-a-string-on-a-delimiter) * [Change a string to lowercase.](#change-a-string-to-lowercase) * [Change a string to uppercase.](#change-a-string-to-uppercase) * [Trim quotes from a string.](#trim-quotes-from-a-string) * [Strip characters from start of string.](#strip-characters-from-start-of-string) * [Strip characters from end of string.](#strip-characters-from-end-of-string) * [Arrays](#arrays) * [Reverse an array.](#reverse-an-array) * [Cycle through an array.](#cycle-through-an-array) * [Toggle between two values.](#toggle-between-two-values) * [File handling](#file-handling) * [Read a file to a string.](#read-a-file-to-a-string) * [Read a file to an array (*by line*).](#read-a-file-to-an-array-by-line) * [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) * [Iterate over files.](#iterate-over-files) * [Count files or directories in directory.](#count-files-or-directories-in-directory) * [Create an empty file.](#create-an-empty-file) * [File Paths](#file-paths) * [Get the directory name of a file path.](#get-the-directory-name-of-a-file-path) * [Get the base-name of a file path.](#get-the-base-name-of-a-file-path) * [Arithmetic](#arithmetic) * [Simpler syntax to set variables.](#simpler-syntax-to-set-variables) * [Ternary tests.](#ternary-tests) * [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) * [Information about the terminal](#information-about-the-terminal) * [Get the terminal size in lines and columns (*from a script*).](#get-the-terminal-size-in-lines-and-columns-from-a-script) * [Get the terminal size in pixels.](#get-the-terminal-size-in-pixels) * [Get the current cursor position.](#get-the-current-cursor-position) * [Miscellaneous](#miscellaneous) * [Get the current date using `strftime`.](#get-the-current-date-using-strftime) ## Strings ### Trim white-space from string. **NOTE**: This also truncates multiple spaces inside the string. ```sh # shellcheck disable=SC2086,SC2048 trim() { # Usage: trim " example string " set -f set -- $* printf '%s\n' "$*" set +f } ``` ### Split a string on a delimiter. ```sh # To multiple variables. string="1,2,3" IFS=, read -r var1 var2 var3 <<< "$string" # To an array. IFS=, read -ra vars <<< "$string" ``` ### Change a string to lowercase. **NOTE:** Requires `bash` 4+ ```sh lower() { # Usage: lower "string" printf '%s\n' "${1,,}" } ``` ### Change a string to uppercase. **NOTE:** Requires `bash` 4+ ```sh upper() { # Usage: upper "string" printf '%s\n' "${1^^}" } ``` ### Trim quotes from a string. ```sh trim_quotes() { # Usage: trim_quotes "string" : "${1//\'}" printf "%s\\n" "${_//\"}" } ``` ### Strip characters from start of string. ```sh lstrip() { # Usage: lstrip "string" "chars to remove" printf '%s\n' "${1##$2}" } ``` ### Strip characters from end of string. ```sh rstrip() { # Usage: rstrip "string" "chars to remove" printf '%s\n' "${1%%$2}" } ``` ## Arrays ### Reverse an array. Enabling `extdebug` allows access to the `BASH_ARGV` array which stores the current function’s arguments in reverse. ```sh reverse_array() { # Usage: reverse_array "array" # reverse_array 1 2 3 4 5 6 shopt -s extdebug f()(printf '%s ' "${BASH_ARGV[@]}"); f "$@" shopt -u extdebug printf '\n' } ``` ### Cycle through an array. Each time the `printf` is called, the next array element is printed. When the print hits the last array element it starts from the first element again. ```sh arr=(a b c d) printf '%s\n' "${arr[$((i==${#arr[@]}-1?i=0:++i))]}" ``` ### Toggle between two values. This works the same as above, this is just a different use case. ```sh arr=(true false) printf '%s\n' "${arr[$((i==${#arr[@]}-1?i=0:++i))]}" ``` ## File handling ### Read a file to a string. Alternative to the `cat` command. ```sh file_data="$(<"file")" ``` ### Read a file to an array (*by line*). Alternative to the `cat` command. ```sh IFS=$'\n' read -d "" -ra file_data < "file" ``` ### 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[@]}" } ``` ### Iterate over files. Don’t use `ls`. ```sh # Greedy example. for file in *; do echo "$file" done # PNG files in dir. for file in ~/Pictures/*.png; do echo "$file" done # Iterate over directories. for dir in ~/Downloads/; do echo "$dir" done # Iterate recursively. shopt -s globstar for file in ~/Pictures/**/*; do echo "$file" done shopt -u globstar ``` ### 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. ```sh count() { # Usage: count /path/to/dir/* # count /path/to/dir/*/ printf '%s\n' "$#" } ``` ### Create an empty file. Alternative to `touch`. ```sh :> file # Longer alternatives: echo -n > file printf '' > file ``` ## File Paths ### Get the directory name of a file path. Alternative to the `dirname` command. ```sh dirname() { # Usage: dirname "path" printf '%s\n' "${1%/*}/" } ``` ### Get the base-name of a file path. Alternative to the `basename` command. ```sh basename() { # Usage: basename "path" : "${1%/}" printf '%s\n' "${_##*/}" } ``` ## Arithmetic ### Simpler syntax to set variables. ```sh # Simple math ((var=1+2)) # Decrement/Increment variable ((var++) ((var--)) ((var+=1)) ((var-=1)) # Using variables ((var=var2*arr[2])) ``` ### Ternary tests. ```sh # 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)) ``` ## 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" "$3" } ``` ## Information about the terminal ### Get the terminal size in lines and columns (*from a script*). This is handy when writing scripts in pure bash and `stty`/`tput` can’t be called. ```sh get_term_size() { # Usage: get_term_size # (:;:) is a micro sleep to ensure the variables are # exported immediately. shopt -s checkwinsize; (:;:) printf '%s\n' "$LINES $COLUMNS" } ``` ### Get the terminal size in pixels. **NOTE**: This does not work in some terminal emulators. ```sh get_window_size() { # Usage: get_window_size printf '%b' "${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]}" } ``` ### Get the current cursor position. This is useful when creating a TUI in pure bash. ```sh get_cursor_pos() { # Usage: get_cursor_pos IFS='[;' read -p $'\e[6n' -d R -rs _ y x _ printf '%s\n' "$x $y" } ``` ## Miscellaneous ### 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" } ```