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.
- 序言
- 字符串
- 数组
- 循环
- 文件处理
- 文件路径
- 变量
- 转义字符串
- 变量扩展
- 花括号扩展
- 条件表达式test
- 算术操作
- 计算
- 捕获信息
- PERFORMANCE
- 旧语法
- 内置变量
- 终端信息
- 转换
- 更简单的代码写法
- 其他
- AFTERWORD
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.
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.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: 这个例子只是获取第一个分组，如果你需要捕获更多分组，则需要根据实际情况进行修改。
注意:
- 不要直接[[ 字符串 =~ 正则表达式 ]] && echo ${BASH_REMATCH[@]}这样把字符串和正则直接放在中括号里，这样会一直没有匹配
- 正则表达式不能使用引号包围
- 这个是bash的正则匹配，直接在zsh终端下，可能会不生效，要先把字符串和正则都设置到两个变量，然后在引用变量来进行匹配
- 方式一，字符串放到变量, tmp_str="abc123def"; [[
$tmp_str =~ .* ]] && echo $ {BASH_REMATCH[@]} - 方式二，两个都放到变量, tmp_str="abc123def";re='.*'; [[ $tmp_str =~
$re ]] && echo $ {BASH_REMATCH[@]} 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.
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
johnCAVEAT: 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"
HELLOCAVEAT: 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"
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 BrownExample 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-bibleExample 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-bibleUsing 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 [[ ${arr[*]} == *sub_string* ]]; then
printf '%s\n' "sub_string is in array."
fiUsing a case statement:
case "$var" in
*sub_string*)
# Do stuff
;;
*sub_string2*)
# Do more stuff
;;
*)
# Else
;;
esacif [[ $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."
fiif [[ $var == *sub_string ]]; then
printf '%s\n' "var ends with sub_string."
fi
# Inverse (var does not end with sub_string).
if [[ $var != *sub_string ]]; then
printf '%s\n' "var does not end with sub_string."
fiEnabling extdebug allows access to the BASH_ARGV array which stores
the current function’s arguments in reverse.
Example Function:
reverse_array() {
# Usage: reverse_array "array"
shopt -s extdebug
f()(printf '%s\n' "${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 "${arr[@]}"
red
green
blueExample Function:
random_array_element() {
# Usage: random_array_element "array"
local arr=("$@")
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
3Each 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))
}Alternative to seq.
# Loop from 0-100 (no variable support).
for i in {0..100}; do
printf '%s\n' "$i"
doneAlternative to seq.
# Loop from 0-VAR.
VAR=50
for ((i=0;i<=VAR;i++)); do
printf '%s\n' "$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
# Brace Expansion.
for file in /path/to/parentdir/{file1,file2,subdir/file3}; do
printf '%s\n' "$file"
done
# Iterate recursively.
shopt -s globstar
for file in ~/Pictures/**/*; do
printf '%s\n' "$file"
done
shopt -u globstarCAVEAT: bash does not handle binary data properly in versions < 4.4.
Alternative to the cat command.
file_data="$(<"file")"Alternative to the cat command.
# Bash <4 (discarding empty lines).
IFS=$'\n' read -d "" -ra file_data < "file"
# Bash <4 (preserving empty lines).
while read -r line; do
file_data+=("$line")
done < "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 works in bash 3 but it is 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 to the function and then counting the number of arguments.
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:
:>file
echo -n >file
printf '' >fileExample Function:
extract() {
# Usage: extract file "opening marker" "closing marker"
while IFS=$'\n' read -r line; do
[[ $extract && $line != "$3" ]] &&
printf '%s\n' "$line"
[[ $line == "$2" ]] && extract=1
[[ $line == "$3" ]] && extract=
done < "$1"
}Example Usage:
# Extract code blocks from MarkDown file.
$ extract ~/projects/pure-bash/README.md '```sh' '```'
# Output here...Alternative to the dirname command.
Example Function:
dirname() {
# Usage: dirname "path"
local tmp=${1:-.}
[[ $tmp != *[!/]* ]] && {
printf '/\n'
return
}
tmp=${tmp%%"${tmp##*[!/]}"}
[[ $tmp != */* ]] && {
printf '.\n'
return
}
tmp=${tmp%/*}
tmp=${tmp%%"${tmp##*[!/]}"}
printf '%s\n' "${tmp:-/}"
}Example Usage:
$ dirname ~/Pictures/Wallpapers/1.jpg
/home/black/Pictures/Wallpapers
$ dirname ~/Pictures/Downloads/
/home/black/PicturesAlternative to the basename command.
Example Function:
basename() {
# Usage: basename "path" ["suffix"]
local tmp
tmp=${1%"${1##*[!/]}"}
tmp=${tmp##*/}
tmp=${tmp%"${2/"$tmp"}"}
printf '%s\n' "${tmp:-/}"
}Example Usage:
$ basename ~/Pictures/Wallpapers/1.jpg
1.jpg
$ basename ~/Pictures/Wallpapers/1.jpg .jpg
1
$ basename ~/Pictures/Downloads/
Downloads$ hello_world="value"
# Create the variable name.
$ var="world"
$ ref="hello_$var"
# Print the value of the variable name stored in 'hello_$var'.
$ printf '%s\n' "${!ref}"
valueAlternatively, on bash 4.3+:
$ hello_world="value"
$ var="world"
# Declare a nameref.
$ declare -n ref=hello_$var
$ printf '%s\n' "$ref"
value$ var="world"
$ declare "hello_$var=value"
$ printf '%s\n' "$hello_world"
valueContrary to popular belief, there is no issue in utilizing raw escape sequences. Using tput abstracts the same ANSI sequences as if printed manually. Worse still, tput is not actually portable. There are a number of tput variants each with different commands and syntaxes (try tput setaf 3 on a FreeBSD system). Raw sequences are fine.
NOTE: Sequences requiring RGB values only work in True-Color Terminal Emulators.
| Sequence | What does it do? | Value |
|---|---|---|
\e[38;5;<NUM>m |
前景颜色. | 0-255 |
\e[48;5;<NUM>m |
背景颜色. | 0-255 |
\e[38;2;<R>;<G>;<B>m |
用RGB设置前景颜色. | R, G, B |
\e[48;2;<R>;<G>;<B>m |
用RGB设置背景颜色. | R, G, B |
| Sequence | What does it do? |
|---|---|
\e[m |
重置. |
\e[1m |
粗体字. |
\e[2m |
模糊文本. |
\e[3m |
斜体字. |
\e[4m |
下划线. |
\e[5m |
闪烁文本. |
\e[7m |
高亮文本. |
\e[8m |
隐藏文本. |
\e[9m |
删除线文字. |
| Sequence | What does it do? | Value |
|---|---|---|
\e[<LINE>;<COLUMN>H |
移动光标到绝对位置. | line, column |
\e[H |
移动光标到初始home位置 (0,0). |
|
\e[<NUM>A |
光标向上N行. | num |
\e[<NUM>B |
光标向下N行. | num |
\e[<NUM>C |
光标向右N列. | num |
\e[<NUM>D |
光标向左N列. | num |
\e[s |
保存光标位置. | |
\e[u |
恢复光标位置. |
| Sequence | What does it do? |
|---|---|
\e[K |
删除光标位置到行尾. |
\e[1K |
删除光标位置到行首. |
\e[2K |
删除整行. |
\e[J |
删除光标所在行到屏幕底部. |
\e[1J |
删除光标所在行到屏幕顶部. |
\e[2J |
清屏. |
\e[2J\e[H |
清屏并光标回到初始位置 0,0. |
| Parameter | What does it do? |
|---|---|
${!VAR} |
根据变量 VAR 的值访问变量，动态变量. |
${!VAR*} |
Expand to IFS separated list of variable names starting with VAR. |
${!VAR@} |
Expand to IFS separated list of variable names starting with VAR. If double-quoted, each variable name expands to a separate word. |
NOTE: #在键盘左边，%在键盘右边，一个#短匹配，两个#长匹配
| Parameter | What does it do? |
|---|---|
${VAR#PATTERN} |
从左边删除最短匹配. |
${VAR##PATTERN} |
从左边删除最长匹配. |
${VAR%PATTERN} |
从右边删除最短匹配. |
${VAR%%PATTERN} |
从右边删除最长匹配. |
${VAR/PATTERN/REPLACE} |
替换第一个匹配项. |
${VAR//PATTERN/REPLACE} |
替换所有匹配项. |
${VAR/PATTERN} |
删除第一个匹配项. |
${VAR//PATTERN} |
删除所有匹配项. |
| Parameter | What does it do? |
|---|---|
${#VAR} |
字符串长度. |
${#ARR[@]} |
数组长度. |
| Parameter | What does it do? |
|---|---|
${VAR:OFFSET} |
删除前N个字符. |
${VAR:OFFSET:LENGTH} |
Get substring from N character to N character. ( ${VAR:10:10}: Get sub-string from char 10 to char 20) |
${VAR:: OFFSET} |
获取前N个字符. |
${VAR:: -OFFSET} |
删除后N个字符. |
${VAR: -OFFSET} |
获取后N个字符. |
${VAR:OFFSET:-OFFSET} |
Cut first N chars and last N chars. |
| Parameter | What does it do? | CAVEAT |
|---|---|---|
${VAR^} |
首字母转大写. | bash 4+ |
${VAR^^} |
转大写. | bash 4+ |
${VAR,} |
首字母小写. | bash 4+ |
${VAR,,} |
转小写. | bash 4+ |
${VAR~} |
首字母大小写切换. | bash 4+ |
${VAR~~} |
所有字母大小写切换. | bash 4+ |
NOTE:
- 有=的两个才会设置VAR的值
- 长（有:） <----对应----> 长（既空也未定义）,短（无:）<----对应---->短（只有未定义）
- 有+的取反
| Parameter | What does it do? | 记忆 |
|---|---|---|
${VAR:-STRING} |
VAR 空或未定义, 用 STRING. |
长 |
${VAR-STRING} |
VAR 未定义, 用 STRING. |
短 |
${VAR:=STRING} |
VAR 空或未定义, 设置 VAR 为 STRING. |
长，有=所以设值 |
${VAR=STRING} |
VAR 未定义, 设置 VAR 为 STRING. |
短，有=所以设值 |
${VAR:+STRING} |
VAR 不为空（!空或未定义）, 用 STRING. |
长，有+所以取反! |
${VAR+STRING} |
VAR 已定义(!未定义）, 用 STRING. |
短，有+所以取反! |
${VAR:?STRING} |
空或未定义，显示err_msg. | 长 |
${VAR?STRING} |
未定义，显示err_msg. | 短 |
# Syntax: {<START>..<END>}
# Print numbers 1-100.
echo {1..100}
# Print range of floats.
echo 1.{1..9}
# Print chars a-z.
echo {a..z}
echo {A..Z}
# Nesting.
echo {A..Z}{0..9}
# Print zero-padded numbers.
# CAVEAT: bash 4+
echo {01..100}
# Change increment amount.
# Syntax: {<START>..<END>..<INCREMENT>}
# CAVEAT: bash 4+
echo {1..10..2} # Increment by 2.echo {apples,oranges,pears,grapes}
# Example Usage:
# Remove dirs Movies, Music and ISOS from ~/Downloads/.
rm -rf ~/Downloads/{Movies,Music,ISOS}| Expression | Value | What does it do? |
|---|---|---|
-a |
file |
文件存在. |
-b |
file |
If file exists and is a block special file. |
-c |
file |
If file exists and is a character special file. |
-d |
file |
文件存在并且是目录. |
-e |
file |
文件存在. |
-f |
file |
If file exists and is a regular file. |
-g |
file |
If file exists and its set-group-id bit is set. |
-h |
file |
I文件存在并且是一个软连接. |
-k |
file |
If file exists and its sticky-bit is set |
-p |
file |
If file exists and is a named pipe (FIFO). |
-r |
file |
文件存在并且可读. |
-s |
file |
If file exists and its size is greater than zero. |
-t |
fd |
If file descriptor is open and refers to a terminal. |
-u |
file |
If file exists and its set-user-id bit is set. |
-w |
file |
文件存在并且可写. |
-x |
file |
文件存在并且可执行. |
-G |
file |
If file exists and is owned by the effective group ID. |
-L |
file |
文件存在并且是一个软连接. |
-N |
file |
If file exists and has been modified since last read. |
-O |
file |
If file exists and is owned by the effective user ID. |
-S |
file |
文件存在并且是一个socket文件. |
| Expression | What does it do? |
|---|---|
file -ef file2 |
If both files refer to the same inode and device numbers. |
file -nt file2 |
If file is newer than file2 (uses modification time) or file exists and file2 does not. |
file -ot file2 |
If file is older than file2 (uses modification time) or file2 exists and file does not. |
| Expression | Value | What does it do? |
|---|---|---|
-o |
opt |
If shell option is enabled. |
-v |
var |
If variable has a value assigned. |
-R |
var |
If variable is a name reference. |
-z |
var |
字符串长度为零. |
-n |
var |
字符串长度不为零. |
| Expression | What does it do? |
|---|---|
var = var2 |
Equal to. |
var == var2 |
Equal to (synonym for =). |
var != var2 |
Not equal to. |
var < var2 |
Less than (in ASCII alphabetical order.) |
var > var2 |
Greater than (in ASCII alphabetical order.) |
| Operators | What does it do? |
|---|---|
= |
Initialize or change the value of a variable. |
| Operators | What does it do? |
|---|---|
+ |
Addition |
- |
Subtraction |
* |
Multiplication |
/ |
Division |
** |
Exponentiation |
% |
Modulo |
+= |
Plus-Equal (Increment a variable.) |
-= |
Minus-Equal (Decrement a variable.) |
*= |
Times-Equal (Multiply a variable.) |
/= |
Slash-Equal (Divide a variable.) |
%= |
Mod-Equal (Remainder of dividing a variable.) |
| Operators | What does it do? |
|---|---|
<< |
Bitwise Left Shift |
<<= |
Left-Shift-Equal |
>> |
Bitwise Right Shift |
>>= |
Right-Shift-Equal |
& |
Bitwise AND |
&= |
Bitwise AND-Equal |
| |
Bitwise OR |
|= |
Bitwise OR-Equal |
~ |
Bitwise NOT |
^ |
Bitwise XOR |
^= |
Bitwise XOR-Equal |
| Operators | What does it do? |
|---|---|
! |
NOT |
&& |
AND |
|| |
OR |
| Operators | What does it do? | Example |
|---|---|---|
, |
Comma Separator | ((a=1,b=2,c=3)) |
# 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))Traps allow a script to execute code on various signals. In pxltrm (a pixel art editor written in bash) traps are used to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit.
Traps should be added near the start of scripts so any early errors are also caught.
NOTE: For a full list of signals, see trap -l.
# Clear screen on script exit.
trap 'printf \\e[2J\\e[H\\e[m' EXITtrap '' INT# Call a function on window resize.
trap 'code_here' SIGWINCHtrap 'code_here' DEBUGtrap 'code_here' RETURNIf unicode is not required, it can be disabled for a performance increase. Results may vary however there have been noticeable improvements in neofetch and other programs.
# Disable unicode.
LC_ALL=C
LANG=CUse #!/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 "$(command)")"Do not use the function keyword, it reduces compatibility with older versions of bash.
# Right.
do_something() {
# ...
}
# Wrong.
function do_something() {
# ...
}"$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"Each time $RANDOM is used, a different integer between 0 and 32767 is returned. This variable should not be used for anything related to security (this includes encryption keys etc).
"$RANDOM"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"
# hex_to_rgb "000000"
: "${1/\#}"
((r=16#${_:0:2},g=16#${_:2:2},b=16#${_:4:2}))
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
# This can be used to assign integer values.
# Example: f a=1
# f a++
f()(($1))
# Using tests, loops etc.
# NOTE: ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’ can also be used.
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
# ...
}The : built-in can be used to avoid repeating variable= in a case statement. The $_ variable stores the last argument of the last command. : always succeeds so it can be used to store the variable value.
# Modified snippet from Neofetch.
case "$OSTYPE" in
"darwin"*)
: "MacOS"
;;
"linux"*)
: "Linux"
;;
*"bsd"* | "dragonfly" | "bitrig")
: "BSD"
;;
"cygwin" | "msys" | "win32")
: "Windows"
;;
*)
printf '%s\n' "Unknown OS detected, aborting..." >&2
exit 1
;;
esac
# Finally, set the variable.
os="$_"Surprisingly, sleep is an external command and not a bash built-in.
CAVEAT: Requires bash 4+
Example Function:
read_sleep() {
# Usage: sleep 1
# sleep 0.2
read -rst "${1:-1}" -N 999
}Example Usage:
read_sleep 1
read_sleep 0.1
read_sleep 30# There are 3 ways to do this and either one can be used.
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 is not installed).
if ! type -p convert &>/dev/null; then
printf '%s\n' "error: convert is not installed, exiting..."
exit 1
fiBash’s printf has a built-in method of getting the date which can be used in place of the date command.
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 AMCAVEAT: Requires bash 4.4+
$ : \\u
# Expand the parameter as if it were a prompt string.
$ printf '%s\n' "${_@P}"
blackCAVEAT: The generated value is not cryptographically secure.
Example Function:
uuid() {
# Usage: uuid
C="89ab"
for ((N=0;N<16;++N)); do
B="$((RANDOM%256))"
case "$N" in
6) printf '4%x' "$((B%16))" ;;
8) printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
3|5|7|9)
printf '%02x-' "$B"
;;
*)
printf '%02x' "$B"
;;
esac
done
printf '\n'
}Example Usage:
$ uuid
d5b6c731-1310-4c24-9fe3-55d556d44374This 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'get_functions() {
# Usage: get_functions
IFS=$'\n' read -d "" -ra functions < <(declare -F)
printf '%s\n' "${functions[@]//declare -f }"
}# alias
ls
# command
# shellcheck disable=SC1001
\ls# function
ls
# command
command lsThis will run the given command and keep it running, even after the terminal or SSH connection is terminated. All output is ignored.
bkr() {
(nohup "$@" &>/dev/null &)
}
bkr ./some_script.sh # some_script.sh is now running in the backgroundThanks for reading! If this bible helped you in any way and you'd like to give back, consider donating. Donations give me the time to make this the best resource possible. Can't donate? That's OK, star the repo and share it with your friends!
Rock on. 🤘