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.
The snippets below are linted using shellcheck and tests have been
written where applicable. If you're looking to contribute, have a read of
the
CONTRIBUTING.md.
It outlines how the unit tests work and what's required when adding
snippets.
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, contribute!
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.
- Strings
- Trim leading and trailing white-space from string.
- Trim all white-space from string and truncate spaces.
- Use REGEX on a string.
- Split a string on a delimiter.
- Change a string to lowercase.
- Change a string to uppercase.
- Trim quotes from a string.
- Strip all instances of pattern from string.
- Strip first occurrence of pattern from string.
- Strip pattern from start of string.
- Strip pattern from end of string.
- Check if string contains a sub-string.
- Check if string starts with sub-string.
- Check if string ends with sub-string.
- Variables
- Arrays
- Loops
- File handling
- File Paths
- Arithmetic
- Obsolete Syntax
- Internal Variables
- Get the location to the
bashbinary. - Get the version of the current running
bashprocess. - Open the user's preferred text editor.
- Get the name of the current function.
- Get the host-name of the system.
- Get the architecture of the Operating System.
- Get the name of the Operating System / Kernel.
- Get the current working directory.
- Get the number of seconds the script has been running.
- Get the location to the
- Information about the terminal
- Colors
- Code Golf
- Other
This is an alternative to sed, awk, perl and other tools. The
function below works by finding all leading and trailing white-space and
removing it from the start and end of the string. The : built-in is used
in place of a temporary variable.
Example Function:
trim_string() {
# Usage: trim_string " example string "
: "${1#"${1%%[![:space:]]*}"}"
: "${_%"${_##*[![:space:]]}"}"
printf '%s\n' "$_"
}Example Usage:
$ trim_string " Hello, World "
Hello, World
$ name=" John Black "
$ trim_string "$name"
John BlackThis is an alternative to sed, awk, perl and other tools. The
function below works by abusing word splitting to create a new string
without leading/trailing white-space and with truncated spaces.
Example Function:
# shellcheck disable=SC2086,SC2048
trim_all() {
# Usage: trim_all " example string "
set -f
set -- $*
printf '%s\n' "$*"
set +f
}Example Usage:
$ trim_all " Hello, World "
Hello, World
$ name=" John Black is my name. "
$ trim_all "$name"
John Black is my name.We can use the result of bash's regex matching to replace sed for a
large number of use-cases.
CAVEAT: This is one of the few platform dependant bash features.
bash will use whatever regex engine is installed on the user's system.
Stick to POSIX regex features if aiming for compatibility.
CAVEAT: This example only prints the first matching group. When using multiple capture groups some modification is needed.
Example Function:
regex() {
# Usage: regex "string" "regex"
[[ $1 =~ $2 ]] && printf '%s\n' "${BASH_REMATCH[1]}"
}Example Usage:
$ # Trim leading white-space.
$ regex ' hello' '^\s*(.*)'
hello
$ # Validate a hex color.
$ regex "#FFFFFF" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$'
#FFFFFF
$ # Validate a hex color (invalid).
$ regex "red" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$'
# no output (invalid)Example Usage in script:
is_hex_color() {
if [[ "$1" =~ ^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$ ]]; then
printf '%s\n' "${BASH_REMATCH[1]}"
else
printf '%s\n' "error: $1 is an invalid color."
return 1
fi
}
read -r color
is_hex_color "$color" || color="#FFFFFF"
# Do stuff.This is an alternative to cut, awk and other tools.
string="1,2,3"
# To multiple variables.
IFS=, read -r var1 var2 var3 <<< "$string"
# To an array.
IFS=, read -ra vars <<< "$string"CAVEAT: Requires bash 4+
Example Function:
lower() {
# Usage: lower "string"
printf '%s\n' "${1,,}"
}Example Usage:
$ lower "HELLO"
hello
$ lower "HeLlO"
hello
$ lower "hello"
helloCAVEAT: Requires bash 4+
Example Function:
upper() {
# Usage: upper "string"
printf '%s\n' "${1^^}"
}Example Usage:
$ upper "hello"
HELLO
$ upper "HeLlO"
HELLO
$ upper "HELLO"
HELLOExample Function:
trim_quotes() {
# Usage: trim_quotes "string"
: "${1//\'}"
printf "%s\\n" "${_//\"}"
}Example Usage:
$ var="'Hello', \"World\""
$ trim_quotes "$var"
Hello, WorldExample Function:
strip_all() {
# Usage: strip_all "string" "pattern"
printf '%s\n' "${1//$2}"
}Example Usage:
$ strip_all "The Quick Brown Fox" "[aeiou]"
Th Qck Brwn Fx
$ strip_all "The Quick Brown Fox" "[[:space:]]"
TheQuickBrownFox
$ strip_all "The Quick Brown Fox" "Quick "
The Brown FoxExample Function:
strip() {
# Usage: strip "string" "pattern"
printf '%s\n' "${1/$2}"
}Example Usage:
$ strip "The Quick Brown Fox" "[aeiou]"
Th Quick Brown Fox
$ strip "The Quick Brown Fox" "[[:space:]]"
TheQuick Brown FoxExample Function:
lstrip() {
# Usage: lstrip "string" "pattern"
printf '%s\n' "${1##$2}"
}Example Usage:
$ lstrip "The Quick Brown Fox" "The "
Quick Brown FoxExample Function:
rstrip() {
# Usage: rstrip "string" "pattern"
printf '%s\n' "${1%%$2}"
}Example Usage:
$ rstrip "The Quick Brown Fox" " Fox"
The Quick BrownUsing a test:
if [[ "$var" == *sub_string* ]]; then
printf '%s\n' "sub_string is in var."
fi
# Inverse (substring not in string).
if [[ "$var" != *sub_string* ]]; then
printf '%s\n' "sub_string is not in var."
fi
# This works for arrays too!
if [[ "${arr[*]}" == *sub_string* ]]; then
printf '%s\n' "sub_string is in array."
fiif [[ "$var" == sub_string* ]]; then
printf '%s\n' "var starts with sub_string."
fi
# Inverse (var doesn't start with sub_string).
if [[ "$var" != sub_string* ]]; then
printf '%s\n' "var does not start with sub_string."
fiif [[ "$var" == *sub_string ]]; then
printf '%s\n' "var ends with sub_string."
fi
# Inverse (var doesn't start with sub_string).
if [[ "$var" != *sub_string ]]; then
printf '%s\n' "var does not end with sub_string."
fiUsing a case statement:
case "$var" in
*sub_string*)
# Do stuff
;;
*sub_string2*)
# Do more stuff
;;
*)
# Else
;;
esachello_world="test"
# Create the variable name.
var1="world"
var2="hello_${var1}"
# Print the value of the variable name stored in 'hello_$var1'.
printf '%s\n' "${!var2}"Enabling extdebug allows access to the BASH_ARGV array which stores
the current function’s arguments in reverse.
Example Function:
reverse_array() {
# Usage: reverse_array "array"
shopt -s extdebug
f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@"
shopt -u extdebug
}Example Usage:
$ reverse_array 1 2 3 4 5
5
4
3
2
1
$ arr=(red blue green)
$ reverse_array "${arr[@]}"
green
blue
redCreate a temporary associative array. When setting associative array values and a duplicate assignment occurs, bash overwrites the key. This allows us to effectively remove array duplicates.
CAVEAT: Requires bash 4+
Example Function:
remove_array_dups() {
# Usage: remove_array_dups "array"
declare -A tmp_array
for i in "$@"; do
[[ "$i" ]] && IFS=" " tmp_array["${i:- }"]=1
done
printf '%s\n' "${!tmp_array[@]}"
}Example Usage:
$ remove_array_dups 1 1 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5
1
2
3
4
5
$ arr=(red red green blue blue)
$ remove_array_dups "${arr[@]}"
red
green
blueEach time the printf is called, the next array element is printed. When
the print hits the last array element it starts from the first element
again.
arr=(a b c d)
cycle() {
printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
}This works the same as above, this is just a different use case.
arr=(true false)
cycle() {
printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
}Don't use seq.
# Loop from 0-100 (no variable support).
for i in {0..100}; do
printf '%s\n' "$i"
doneDon't use seq.
# Loop from 0-VAR.
VAR=50
for ((i=0;i<=VAR;i++)); do
printf '%s\n' "$i"
donearr=(apples oranges tomatoes)
# Just elements.
for element in "${arr[@]}"; do
printf '%s\n' "$element"
donearr=(apples oranges tomatoes)
# Elements and index.
for i in "${!arr[@]}"; do
printf '%s\n' "${arr[$i]}"
done
# Alternative method.
for ((i=0;i<${#arr[@]};i++)); do
printf '%s\n' "${arr[$i]}"
donewhile read -r line; do
printf '%s\n' "$line"
done < "file"Don’t use ls.
# Greedy example.
for file in *; do
printf '%s\n' "$file"
done
# PNG files in dir.
for file in ~/Pictures/*.png; do
printf '%s\n' "$file"
done
# Iterate over directories.
for dir in ~/Downloads/*/; do
printf '%s\n' "$dir"
done
# Iterate recursively.
shopt -s globstar
for file in ~/Pictures/**/*; do
printf '%s\n' "$file"
done
shopt -u globstarCAVEAT: bash doesn't handle binary data properly in versions < 4.4.
Alternative to the cat command.
file_data="$(<"file")"Alternative to the cat command.
# Bash <4
IFS=$'\n' read -d "" -ra file_data < "file"
# Bash 4+
mapfile -t file_data < "file"Alternative to the head command.
CAVEAT: Requires bash 4+
Example Function:
head() {
# Usage: head "n" "file"
mapfile -tn "$1" line < "$2"
printf '%s\n' "${line[@]}"
}Example Usage:
$ head 2 ~/.bashrc
# Prompt
PS1='➜ '
$ head 1 ~/.bashrc
# PromptAlternative to the tail command.
CAVEAT: Requires bash 4+
Example Function:
tail() {
# Usage: tail "n" "file"
mapfile -tn 0 line < "$2"
printf '%s\n' "${line[@]: -$1}"
}Example Usage:
$ tail 2 ~/.bashrc
# Enable tmux.
# [[ -z "$TMUX" ]] && exec tmux
$ tail 1 ~/.bashrc
# [[ -z "$TMUX" ]] && exec tmuxAlternative to wc -l.
Example Function (bash 4):
lines() {
# Usage: lines "file"
mapfile -tn 0 lines < "$1"
printf '%s\n' "${#lines[@]}"
}Example Function (bash 3):
This method uses less memory than the mapfile method and it's more
compatible but it's slower for bigger files.
lines_loop() {
# Usage: lines_loop "file"
count=0
while IFS= read -r _; do
((count++))
done < "$1"
printf '%s\n' "$count"
}Example Usage:
$ lines ~/.bashrc
48
$ lines_loop ~/.bashrc
48This works by passing the output of the glob as function arguments. We then count the arguments and print the number.
Example Function:
count() {
# Usage: count /path/to/dir/*
# count /path/to/dir/*/
printf '%s\n' "$#"
}Example Usage:
# Count all files in dir.
$ count ~/Downloads/*
232
# Count all dirs in dir.
$ count ~/Downloads/*/
45
# Count all jpg files in dir.
$ count ~/Pictures/*.jpg
64Alternative to touch.
# Shortest.
:> file
# Longer alternatives:
echo -n > file
printf '' > fileAlternative to the dirname command.
Example Function:
dirname() {
# Usage: dirname "path"
printf '%s\n' "${1%/*}/"
}Example Usage:
$ dirname ~/Pictures/Wallpapers/1.jpg
/home/black/Pictures/Wallpapers/
$ dirname ~/Pictures/Downloads/
/home/black/Pictures/Alternative to the basename command.
Example Function:
basename() {
# Usage: basename "path"
: "${1%/}"
printf '%s\n' "${_##*/}"
}Example Usage:
$ basename ~/Pictures/Wallpapers/1.jpg
1.jpg
$ basename ~/Pictures/Downloads/
Downloads# Simple math
((var=1+2))
# Decrement/Increment variable
((var++))
((var--))
((var+=1))
((var-=1))
# Using variables
((var=var2*arr[2]))# 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))Use #!/usr/bin/env bash instead of #!/bin/bash.
- The former searches the user's
PATHto find thebashbinary. - The latter assumes it is always installed to
/bin/which can cause issues.
# Right:
#!/usr/bin/env bash
# Wrong:
#!/bin/bashUse $() instead of ` `.
# Right.
var="$(command)"
# Wrong.
var=`command`
# $() can easily be nested whereas `` cannot.
var="$(command "$(command)")"Don't use the function keyword, it reduces compatibility with older versions of bash.
# Right.
do_something() {
# ...
}
# Wrong.
function do_something() {
# ...
}NOTE: This list does not include every internal variable (You can help by adding a missing entry!).
For a complete list, see: http://tldp.org/LDP/abs/html/internalvariables.html
"$BASH"# As a string.
"$BASH_VERSION"
# As an array.
"${BASH_VERSINFO[@]}""$EDITOR" "$file"
# NOTE: This variable may be empty, set a fallback value.
"${EDITOR:-vi}" "$file"# Current function.
"${FUNCNAME[0]}"
# Parent function.
"${FUNCNAME[1]}"
# So on and so forth.
"${FUNCNAME[2]}"
"${FUNCNAME[3]}"
# All functions including parents.
"${FUNCNAME[@]}""$HOSTNAME"
# NOTE: This variable may be empty.
# Optionally set a fallback to the hostname command.
"${HOSTNAME:-$(hostname)}""$HOSTTYPE"This can be used to add conditional support for different Operating
Systems without needing to call uname.
"$OSTYPE"This is an alternative to the pwd built-in.
"$PWD""$SECONDS"This is handy when writing scripts in pure bash and stty/tput can’t be
called.
Example Function:
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"
}Example Usage:
# Output: LINES COLUMNS
$ get_term_size
15 55CAVEAT: This does not work in some terminal emulators.
Example Function:
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]}"
}Example Usage:
# Output: WIDTHxHEIGHT
$ get_window_size
1200x800
# Output (fail):
$ get_window_size
xThis is useful when creating a TUI in pure bash.
Example Function:
get_cursor_pos() {
# Usage: get_cursor_pos
IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
printf '%s\n' "$x $y"
}Example Usage:
# Output: X Y
$ get_cursor_pos
1 8Example Function:
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"
}Example Usage:
$ hex_to_rgb "#FFFFFF"
255 255 255Example Function:
rgb_to_hex() {
# Usage: rgb_to_hex "r" "g" "b"
printf '#%02x%02x%02x\n' "$1" "$2" "$3"
}Example Usage:
$ rgb_to_hex "255" "255" "255"
#FFFFFF# Tiny C Style.
for((;i++<10;)){ echo "$i";}
# Undocumented method.
for i in {1..10};{ echo "$i";}
# Expansion.
for i in {1..10}; do echo "$i"; done
# C Style.
for((i=0;i<=10;i++)); do echo "$i"; done# Normal method
while :; do echo hi; done
# Shorter
for((;;)){ echo hi;}# Normal method
f(){ echo hi;}
# Using a subshell
f()(echo hi)
# Using arithmetic
# You can use this to assign integer values.
# Example: f a=1
# f a++
f()(($1))
# Using tests, loops etc.
# NOTE: You can also use ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’.
f()if true; then echo "$1"; fi
f()for i in "$@"; do echo "$i"; done# One line
# Note: The 3rd statement may run when the 1st is true
[[ "$var" == hello ]] && echo hi || echo bye
[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
# Multi line (no else, single statement)
# Note: The exit status may not be the same as with an if statement
[[ "$var" == hello ]] && \
echo hi
# Multi line (no else)
[[ "$var" == hello ]] && {
echo hi
# ...
}We can use the : builtin to avoid repeating variable= in a case
statement. The $_ variable stores the last argument of the last
successful command. : always succeeds so we can abuse it to store the
variable value.
# Example snippet from Neofetch.
case "$(uname)" in
"Linux" | "GNU"*)
: "Linux"
;;
*"BSD" | "DragonFly" | "Bitrig")
: "BSD"
;;
"CYGWIN"* | "MSYS"* | "MINGW"*)
: "Windows"
;;
*)
printf '%s\n' "Unknown OS detected, aborting..." >&2
exit 1
;;
esac
# Finally, set the variable.
os="$_"I was surprised to find out sleep is an external command and isn't a
built-in.
Example Funcrion:
read_sleep() {
# Usage: sleep 1
# sleep 0.2
read -rst "${1:-1}" -N 999
}Example Usage:
read_sleep 1
read_sleep 0.1
read_sleep 30# There are 3 ways to do this and you can use either of
# these in the same way.
type -p executable_name &>/dev/null
hash executable_name &>/dev/null
command -v executable_name &>/dev/null
# As a test.
if type -p executable_name &>/dev/null; then
# Program is in PATH.
fi
# Inverse.
if ! type -p executable_name &>/dev/null; then
# Program is not in PATH.
fi
# Example (Exit early if program isn't installed).
if ! type -p convert &>/dev/null; then
printf '%s\n' "error: convert isn't installed, exiting..."
exit 1
fiBash’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.
CAVEAT: Requires bash 4+
Example Function:
date() {
# Usage: date "format"
# See: 'man strftime' for format.
printf "%($1)T\\n" "-1"
}Example Usage:
# Using above function.
$ date "%a %d %b - %l:%M %p"
Fri 15 Jun - 10:00 AM
# Using printf directly.
$ printf '%(%a %d %b - %l:%M %p)T\n' "-1"
Fri 15 Jun - 10:00 AM
# Assigning a variable using printf.
$ printf -v date '%(%a %d %b - %l:%M %p)T\n' '-1'
$ printf '%s\n' "$date"
Fri 15 Jun - 10:00 AMThis is a simple way of drawing progress bars without needing a for loop in the function itself.
Example Function:
bar() {
# Usage: bar 1 10
# ^----- Elapsed Percentage (0-100).
# ^-- Total length in chars.
((elapsed=$1*$2/100))
# Create the bar with spaces.
printf -v prog "%${elapsed}s"
printf -v total "%$(($2-elapsed))s"
printf '%s\r' "[${prog// /-}${total}]"
}Example Usage:
for ((i=0;i<=100;i++)); do
# Pure bash micro sleeps (for the example).
(:;:) && (:;:) && (:;:) && (:;:) && (:;:)
# Print the bar.
bar "$i" "10"
done
printf '\n'# alias
ls
# command
# shellcheck disable=SC1001
\ls# function
ls
# command
command ls