7.3 KiB
pure bash
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, 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
Read a file to a string.
Alternative to the cat command.
file_data="$(<"file")"
Read a file to an array (by line).
Alternative to the cat command.
IFS=$'\n' read -d "" -ra file_data < "file"
Get the first N lines of a file.
Alternative to the head command.
NOTE: Requires bash 4+
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+
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+
lines() {
# Usage lines "file"
mapfile -tn 0 lines < "$1"
printf '%s\n' "${#lines[@]}"
}
Create an empty file.
Alternative to touch.
:> file
# Longer alternatives:
echo -n > file
printf '' > file
Strings
Trim white-space from string.
NOTE: This also truncates multiple spaces inside the string.
# shellcheck disable=SC2086,SC2048
trim() {
# Usage: trim " example string "
set -f
set -- $*
printf '%s\n' "$*"
set +f
}
Split a string on a delimiter.
# 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+
lower() {
# Usage: lower "string"
printf '%s\n' "${1,,}"
}
Change a string to uppercase.
NOTE: Requires bash 4+
upper() {
# Usage: upper "string"
printf '%s\n' "${1^^}"
}
Trim quotes from a string.
trim_quotes() {
# Usage: trim_quotes "string"
: "${1//\'}"
printf "%s\\n" "${_//\"}"
}
Strip characters from start of string.
lstrip() {
# Usage: lstrip "string" "chars to remove"
printf '%s\n' "${1##$2}"
}
Strip characters from end of string.
rstrip() {
# Usage: rstrip "string" "chars to remove"
printf '%s\n' "${1%%$2}"
}
Arrays
Reverse an array.
Enabling extdebug allows access to the BASH_ARGV array which stores
the current function’s arguments in reverse.
reverse_array() {
# Usage: reverse_array "array"
# reverse_array 1 2 3 4 5 6
shopt -s extdebug
f()(printf '%s ' "${BASH_ARGV[@]}"); f "$@"
shopt -u extdebug
printf '\n'
}
File Paths
Get the directory name of a file path.
Alternative to the dirname command.
dirname() {
# Usage: dirname "path"
printf '%s\n' "${1%/*}/"
}
Get the base-name of a file path.
Alternative to the basename command.
basename() {
# Usage: basename "path"
: "${1%/}"
printf '%s\n' "${_##*/}"
}
Colors
Convert a hex color to RGB.
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.
rgb_to_hex() {
# Usage: rgb_to_hex "r" "g" "b"
printf '#%02x%02x%02x\n' "$1" "$2" "$3"
}
Information about the terminal.
Get the terminal size in lines and columns (from a script).
This is handy when writing scripts in pure bash and stty/tput can’t be
called.
get_term_size() {
# Usage: get_term_size
# (:;:) is a micro sleep to ensure the variables are
# exported immediately.
shopt -s checkwinsize; (:;:)
printf '%s\n' "$LINES $COLUMNS"
}
Get the terminal size in pixels.
NOTE: This does not work in some terminal emulators.
get_window_size() {
# Usage: get_window_size
printf '%b' "${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.
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+
date() {
# Usage: date "format"
# See: 'man strftime' for format.
printf "%($1)T\\n"
}