pure bash bible
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.
Table of Contents
- 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
- Colors
- Information about the terminal
- Code Golf
- 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
- Other
Strings
Trim leading and trailing white-space from string.
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 Black
Trim all white-space from string and truncate spaces.
This 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.
Use REGEX on a string.
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.
Split a string on a delimiter.
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"
Change a string to lowercase.
CAVEAT: Requires bash 4+
Example Function:
lower() {
# Usage: lower "string"
printf '%s\n' "${1,,}"
}
Example Usage:
$ lower "HELLO"
hello
$ lower "HeLlO"
hello
$ lower "hello"
hello
Change a string to uppercase.
CAVEAT: Requires bash 4+
Example Function:
upper() {
# Usage: upper "string"
printf '%s\n' "${1^^}"
}
Example Usage:
$ upper "hello"
HELLO
$ upper "HeLlO"
HELLO
$ upper "HELLO"
HELLO
Trim quotes from a string.
Example Function:
trim_quotes() {
# Usage: trim_quotes "string"
: "${1//\'}"
printf "%s\\n" "${_//\"}"
}
Example Usage:
$ var="'Hello', \"World\""
$ trim_quotes "$var"
Hello, World
Strip all instances of pattern from string.
Example Function:
strip_all() {
# Usage: strip_all "string" "pattern"
printf '%s\n' "${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 Fox
Strip first occurrence of pattern from string.
Example 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 Fox
Strip pattern from start of string.
Example Function:
lstrip() {
# Usage: lstrip "string" "pattern"
printf '%s\n' "${1##$2}"
}
Example Usage:
$ lstrip "The Quick Brown Fox" "The "
Quick Brown Fox
Strip pattern from end of string.
Example Function:
rstrip() {
# Usage: rstrip "string" "pattern"
printf '%s\n' "${1%%$2}"
}
Example Usage:
$ rstrip "The Quick Brown Fox" " Fox"
The Quick Brown
Check if string contains a sub-string.
Using 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 [[ "${arr[*]}" == *sub_string* ]]; then
printf '%s\n' "sub_string is in array."
fi
Check if string starts with sub-string.
if [[ "$var" == sub_string* ]]; then
printf '%s\n' "var starts with sub_string."
fi
# Inverse (var doesn't start with sub_string).
if [[ "$var" != sub_string* ]]; then
printf '%s\n' "var does not start with sub_string."
fi
Check if string ends with sub-string.
if [[ "$var" == *sub_string ]]; then
printf '%s\n' "var ends with sub_string."
fi
# Inverse (var doesn't start with sub_string).
if [[ "$var" != *sub_string ]]; then
printf '%s\n' "var does not end with sub_string."
fi
Using a case statement:
case "$var" in
*sub_string*)
# Do stuff
;;
*sub_string2*)
# Do more stuff
;;
*)
# Else
;;
esac
Variables
Assign and access a variable using a variable.
hello_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' "${!var2}"
Arrays
Reverse an array.
Enabling extdebug allows access to the BASH_ARGV array which stores the current function’s arguments in reverse.
Example Function:
reverse_array() {
# Usage: reverse_array "array"
shopt -s extdebug
f()(printf '%s\n' "${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 "${arr[@]}"
green
blue
red
Remove duplicate array elements.
Create a temporary associative array. When setting associative array values and a duplicate assignment occurs, bash overwrites the key. This allows us to effectively remove array duplicates.
CAVEAT: Requires bash 4+
Example Function:
remove_array_dups() {
# Usage: remove_array_dups "array"
declare -A tmp_array
for i in "$@"; 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 "${arr[@]}"
red
green
blue
Cycle through an array.
Each time the printf is called, the next array element is printed. When the print hits the last array element it starts from the first element again.
arr=(a b c d)
cycle() {
printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
}
Toggle between two values.
This works the same as above, this is just a different use case.
arr=(true false)
cycle() {
printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
}
Loops
Loop over a range of numbers.
Don't use seq.
# Loop from 0-100 (no variable support).
for i in {0..100}; do
printf '%s\n' "$i"
done
Loop over a variable range of numbers.
Don't use seq.
# Loop from 0-VAR.
VAR=50
for ((i=0;i<=VAR;i++)); do
printf '%s\n' "$i"
done
Loop over an array.
arr=(apples oranges tomatoes)
# Just elements.
for element in "${arr[@]}"; do
printf '%s\n' "$element"
done
Loop over an array with an index.
arr=(apples oranges tomatoes)
# Elements and index.
for i in "${!arr[@]}"; do
printf '%s\n' "${arr[$i]}"
done
# Alternative method.
for ((i=0;i<${#arr[@]};i++)); do
printf '%s\n' "${arr[$i]}"
done
Loop over the contents of a file.
while read -r line; do
printf '%s\n' "$line"
done < "file"
Loop over files and directories.
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 globstar
File handling
Read a file to a string.
Alternative to the cat command.
file_data="$(<"file")"
Read a file to an array (by line).
Alternative to the cat command.
# Bash <4
IFS=$'\n' read -d "" -ra file_data < "file"
# Bash 4+
mapfile -t file_data < "file"
Get the first N lines of a 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
# Prompt
Get the last N lines of a file.
Alternative 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 tmux
Get the number of lines in a file.
Alternative to wc -l.
CAVEAT: Requires bash 4+
Example Function:
lines() {
# Usage lines "file"
mapfile -tn 0 lines < "$1"
printf '%s\n' "${#lines[@]}"
}
Example Usage:
$ lines ~/.bashrc
48
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.
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
64
Create an empty file.
Alternative to touch.
# Shortest.
:> file
# Longer alternatives:
echo -n > file
printf '' > file
File Paths
Get the directory name of a file path.
Alternative 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/
Get the base-name of a file path.
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
Arithmetic
Simpler syntax to set variables.
# Simple math
((var=1+2))
# Decrement/Increment variable
((var++))
((var--))
((var+=1))
((var-=1))
# Using variables
((var=var2*arr[2]))
Ternary tests.
# 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.
Example 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"
255 255 255
Convert an RGB color to hex.
Example 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
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.
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 55
Get the terminal size in pixels.
CAVEAT: 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
x
Get the current cursor position.
This 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 8
Code Golf
Shorter for loop syntax.
# 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
Shorter infinite loops.
# Normal method
while :; do echo hi; done
# Shorter
for((;;)){ echo hi;}
Shorter function declaration.
# 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 "$i"; done
Shorter if syntax.
# One line
[[ "$var" == hello ]] && echo hi || echo bye
[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
# Multi line (no else, single statement)
[[ "$var" == hello ]] && \
echo hi
# Multi line (no else)
[[ "$var" == hello ]] && {
echo hi
# ...
}
Simpler case statement to set variable.
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="$_"
Internal Variables
NOTE: This list does not include every internal variable (You can help by adding a missing entry!).
For a complete list, see: http://tldp.org/LDP/abs/html/internalvariables.html
Get the location to the bash binary.
"$BASH"
Get the version of the current running bash process.
# As a string.
"$BASH_VERSION"
# As an array.
"${BASH_VERSINFO[@]}"
Open the user's preferred text editor.
"$EDITOR" "$file"
# NOTE: This variable may be empty, set a fallback value.
"${EDITOR:-vi}" "$file"
Get the name of the current function.
# Current function.
"${FUNCNAME[0]}"
# Parent function.
"${FUNCNAME[1]}"
# So on and so forth.
"${FUNCNAME[2]}"
"${FUNCNAME[3]}"
# All functions including parents.
"${FUNCNAME[@]}"
Get the host-name of the system.
"$HOSTNAME"
# NOTE: This variable may be empty.
# Optionally set a fallback to the hostname command.
"${HOSTNAME:-$(hostname)}"
Get the architecture of the Operating System.
"$HOSTTYPE"
Get the name of the Operating System / Kernel.
This can be used to add conditional support for different Operating Systems without needing to call uname.
"$OSTYPE"
Get the current working directory.
This is an alternative to the pwd built-in.
"$PWD"
Get the number of seconds the script has been running.
"$SECONDS"
Other
Use read as an alternative to the sleep command.
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
Check if a program is in the user's PATH.
# 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
fi
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.
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 AM
Progress bars.
This 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'
Bypass shell aliases.
# alias
ls
# command
# shellcheck disable=SC1001
\ls
Bypass shell functions.
# function
ls
# command
command ls
