NEW: pure sh bible (📖 A collection of pure POSIX sh alternatives to external processes).
pure bash bible
A collection of pure bash alternatives to external
processes.
The goal of this book is to document commonly-known and lesser-known methods of doing various tasks using only built-in bash features. Using the snippets from this bible can help remove unneeded dependencies from scripts and in most cases make them faster. I came across these tips and discovered a few while developing neofetch, pxltrm and other smaller projects.
The snippets below are linted using shellcheck and tests have been written where applicable. Want to contribute? Read the CONTRIBUTING.md. It outlines how the unit tests work and what is required when adding snippets to the bible.
See something incorrectly described, buggy or outright wrong? Open an issue or send a pull request. If the bible is missing something, open an issue and a solution will be found.
This book is also available to purchase on leanpub. https://leanpub.com/bash
Or you can buy me a coffee.
Table of Contents
FOREWORD
A collection of pure bash alternatives to external processes and programs. The bash scripting language is more powerful than people realise and most tasks can be accomplished without depending on external programs.
Calling an external process in bash is expensive and excessive use will cause a noticeable slowdown. Scripts and programs written using built-in methods (where applicable) will be faster, require fewer dependencies and afford a better understanding of the language itself.
The contents of this book provide a reference for solving problems encountered when writing programs and scripts in bash. Examples are in function formats showcasing how to incorporate these solutions into code.
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
The result of bash's regex matching can be used to replace sed for a
large number of use-cases.
CAVEAT: This is one of the few platform dependent 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
CAVEAT: Requires bash 4+
This is an alternative to cut, awk and other tools.
Example Function:
split() {
# Usage: split "string" "delimiter"
IFS=$'\n' read -d "" -ra arr <<< "${1//$2/$'\n'}"
printf '%s\n' "${arr[@]}"
}
Example Usage:
$ split "apples,oranges,pears,grapes" ","
apples
oranges
pears
grapes
$ split "1, 2, 3, 4, 5" ", "
1
2
3
4
5
# Multi char delimiters work too!
$ split "hello---world---my---name---is---john" "---"
hello
world
my
name
is
john
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
Reverse a string case
CAVEAT: Requires bash 4+
Example Function:
reverse_case() {
# Usage: reverse_case "string"
printf '%s\n' "${1~~}"
}
Example Usage:
$ reverse_case "hello"
HELLO
$ reverse_case "HeLlO"
hElLo
$ reverse_case "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
Percent-encode a string
Example Function:
urlencode() {
# Usage: urlencode "string"
local LC_ALL=C
for (( i = 0; i < ${#1}; i++ )); do
: "${1:i:1}"
case "$_" in
[a-zA-Z0-9.~_-])
printf '%s' "$_"
;;
*)
printf '%%%02X' "'$_"
;;
esac
done
printf '\n'
}
Example Usage:
$ urlencode "https://github.com/dylanaraps/pure-bash-bible"
https%3A%2F%2Fgithub.com%2Fdylanaraps%2Fpure-bash-bible
Decode a percent-encoded string
Example Function:
urldecode() {
# Usage: urldecode "string"
: "${1//+/ }"
printf '%b\n' "${_//%/\\x}"
}
Example Usage:
$ urldecode "https%3A%2F%2Fgithub.com%2Fdylanaraps%2Fpure-bash-bible"
https://github.com/dylanaraps/pure-bash-bible
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 [[ ${arr[*]} == *sub_string* ]]; then
printf '%s\n' "sub_string is in array."
fi
Using a case statement:
case "$var" in
*sub_string*)
# Do stuff
;;
*sub_string2*)
# Do more stuff
;;
*)
# Else
;;
esac
Check if string starts with sub-string
if [[ $var == sub_string* ]]; then
printf '%s\n' "var starts with sub_string."
fi
# Inverse (var does not 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 does not end with sub_string).
if [[ $var != *sub_string ]]; then
printf '%s\n' "var does not end with sub_string."
fi
ARRAYS
Reverse an array
Enabling extdebug allows access to the BASH_ARGV array which stores
the current function’s arguments in reverse.
CAVEAT: Requires shopt -s compat44 in bash 5.0+.
Example Function:
reverse_array() {
# Usage: reverse_array "array"
shopt -s extdebug
f()(printf '%s\n' "${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 "${arr[@]}"
green
blue
red
Remove duplicate array elements
Create a temporary associative array. When setting associative array
values and a duplicate assignment occurs, bash overwrites the key. This
allows us to effectively remove array duplicates.
CAVEAT: Requires bash 4+
CAVEAT: List order may not stay the same.
Example Function:
remove_array_dups() {
# Usage: remove_array_dups "array"
declare -A tmp_array
for i in "$@"; 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 "${arr[@]}"
red
green
blue
Random array element
Example Function:
random_array_element() {
# Usage: random_array_element "array"
local arr=("$@")
printf '%s\n' "${arr[RANDOM % $#]}"
}
Example Usage:
$ array=(red green blue yellow brown)
$ random_array_element "${array[@]}"
yellow
# Multiple arguments can also be passed.
$ random_array_element 1 2 3 4 5 6 7
3
Cycle thr
这是一份纯 Bash 函数的参考合集，用来替代 sed、awk、cut、grep 等外部工具，完成常见的字符串、数组、文件和终端操作。