字符串

字符串包含

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

字符串开始

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

字符串结尾

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

循环

数字范围循环

Alternative to seq.

# Loop from 0-100 (no variable support).
for i in {0..100}; do
    printf '%s\n' "$i"
done

变量循环

Alternative to seq.

# Loop from 0-VAR.
VAR=50
for ((i=0;i<=VAR;i++)); do
    printf '%s\n' "$i"
done

数组遍历

arr=(apples oranges tomatoes)

# Just elements.
for element in "${arr[@]}"; do
    printf '%s\n' "$element"
done

索引遍历

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

文件或者目录遍历

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 globstar

文件处理

CAVEAT: bash does not handle binary data properly in versions < 4.4.

将文件读取为字符串

Alternative to the cat command.

file_data="$(<"file")"

将文件按行读取成数组

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"

获取文件头部的 N 行

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

获取尾部 N 行

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

获取文件行数

Alternative 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
48

计算文件或者文件夹数量

This 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
64

创建临时文件

Alternative to touch.

# Shortest.
>file

# Longer alternatives:
:>file
echo -n >file
printf '' >file

在两个标记之间抽取 N 行

Example 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...

文件路径

获取文件的目录

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/Pictures

获取文件路径的 base-name

Alternative 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

变量

变量声明和使用

$ 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}"
value

Alternatively, on bash 4.3+:

$ hello_world="value"
$ var="world"

# Declare a nameref.
$ declare -n ref=hello_$var

$ printf '%s\n' "$ref"
value

基于变量命名变量

$ var="world"
$ declare "hello_$var=value"
$ printf '%s\n' "$hello_world"
value

ESCAPE SEQUENCES

Contrary 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.

文本颜色

NOTE: Sequences requiring RGB values only work in True-Color Terminal Emulators.

Sequence	What does it do?	Value
`\e[38;5;<NUM>m`	Set text foreground color.	`0-255`
`\e[48;5;<NUM>m`	Set text background color.	`0-255`
`\e[38;2;<R>;<G>;<B>m`	Set text foreground color to RGB color.	`R`, `G`, `B`
`\e[48;2;<R>;<G>;<B>m`	Set text background color to RGB color.	`R`, `G`, `B`

文本属性

NOTE: Prepend 2 to any code below to turn it’s effect off(examples: 21=bold text off, 22=faint text off, 23=italic text off).

Sequence	What does it do?
`\e[m`	Reset text formatting and colors.
`\e[1m`	Bold text.
`\e[2m`	Faint text.
`\e[3m`	Italic text.
`\e[4m`	Underline text.
`\e[5m`	Blinking text.
`\e[7m`	Highlighted text.
`\e[8m`	Hidden text.
`\e[9m`	Strike-through text.

光标移动

Sequence	What does it do?	Value
`\e[<LINE>;<COLUMN>H`	Move cursor to absolute position.	`line`, `column`
`\e[H`	Move cursor to home position (`0,0`).
`\e[<NUM>A`	Move cursor up N lines.	`num`
`\e[<NUM>B`	Move cursor down N lines.	`num`
`\e[<NUM>C`	Move cursor right N columns.	`num`
`\e[<NUM>D`	Move cursor left N columns.	`num`
`\e[s`	Save cursor position.
`\e[u`	Restore cursor position.

文本擦除

Sequence	What does it do?
`\e[K`	Erase from cursor position to end of line.
`\e[1K`	Erase from cursor position to start of line.
`\e[2K`	Erase the entire current line.
`\e[J`	Erase from the current line to the bottom of the screen.
`\e[1J`	Erase from the current line to the top of the screen.
`\e[2J`	Clear the screen.
`\e[2J\e[H`	Clear the screen and move cursor to `0,0`.

参数展开

指令

Parameter	What does it do?
`${!VAR}`	Access a variable based on the value of `VAR`.
`${!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.

替换

Parameter	What does it do?
`${VAR#PATTERN}`	Remove shortest match of pattern from start of string.
`${VAR##PATTERN}`	Remove longest match of pattern from start of string.
`${VAR%PATTERN}`	Remove shortest match of pattern from end of string.
`${VAR%%PATTERN}`	Remove longest match of pattern from end of string.
`${VAR/PATTERN/REPLACE}`	Replace first match with string.
`${VAR//PATTERN/REPLACE}`	Replace all matches with string.
`${VAR/PATTERN}`	Remove first match.
`${VAR//PATTERN}`	Remove all matches.

长度

Parameter	What does it do?
`${#VAR}`	Length of var in characters.
`${#ARR[@]}`	Length of array in elements.

展开

Parameter	What does it do?
`${VAR:OFFSET}`	Remove first `N` chars from variable.
`${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}`	Get first `N` chars from variable.
`${VAR:: -OFFSET}`	Remove last `N` chars from variable.
`${VAR: -OFFSET}`	Get last `N` chars from variable.
`${VAR:OFFSET:-OFFSET}`	Cut first `N` chars and last `N` chars.

大小写修改

Parameter	What does it do?	CAVEAT
`${VAR^}`	Uppercase first character.	`bash 4+`
`${VAR^^}`	Uppercase all characters.	`bash 4+`
`${VAR,}`	Lowercase first character.	`bash 4+`
`${VAR,,}`	Lowercase all characters.	`bash 4+`
`${VAR~}`	Reverse case of first character.	`bash 4+`
`${VAR~~}`	Reverse case of all characters.	`bash 4+`

默认值

Parameter	What does it do?
`${VAR:-STRING}`	If `VAR` is empty or unset, use `STRING` as its value.
`${VAR-STRING}`	If `VAR` is unset, use `STRING` as its value.
`${VAR:=STRING}`	If `VAR` is empty or unset, set the value of `VAR` to `STRING`.
`${VAR=STRING}`	If `VAR` is unset, set the value of `VAR` to `STRING`.
`${VAR:+STRING}`	If `VAR` is not empty, use `STRING` as its value.
`${VAR+STRING}`	If `VAR` is set, use `STRING` as its value.
`${VAR:?STRING}`	Display an error if empty or unset.
`${VAR?STRING}`	Display an error if unset.

大括号展开

范围

# 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.

字符串列表

echo {apples,oranges,pears,grapes}

# Example Usage:
# Remove dirs Movies, Music and ISOS from ~/Downloads/.
rm -rf ~/Downloads/{Movies,Music,ISOS}

条件表达式

文件条件判断

Expression	Value	What does it do?
`-a`	`file`	If file exists.
`-b`	`file`	If file exists and is a block special file.
`-c`	`file`	If file exists and is a character special file.
`-d`	`file`	If file exists and is a directory.
`-e`	`file`	If file exists.
`-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`	If file exists and is a symbolic link.
`-k`	`file`	If file exists and its sticky-bit is set
`-p`	`file`	If file exists and is a named pipe (FIFO).
`-r`	`file`	If file exists and is readable.
`-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`	If file exists and is writable.
`-x`	`file`	If file exists and is executable.
`-G`	`file`	If file exists and is owned by the effective group ID.
`-L`	`file`	If file exists and is a symbolic link.
`-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`	If file exists and is a socket.

文件比较

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.

变量测试

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`	If the length of string is zero.
`-n`	`var`	If the length of string is non-zero.

变量比较

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.)

算数操作

赋值

Operators	What does it do?
`=`	Initialize or change the value of a variable.

算数

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.)

位操作

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

逻辑

Operators	What does it do?
`!`	NOT
`&&`	AND
`\|\|`	OR

Miscellaneous

Operators	What does it do?	Example
`,`	Comma Separator	`((a=1,b=2,c=3))`

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))

TRAPS

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.

Do something on script exit

# Clear screen on script exit.
trap 'printf \\e[2J\\e[H\\e[m' EXIT

Ignore terminal interrupt (CTRL+C, SIGINT)

trap '' INT

React to window resize

# Call a function on window resize.
trap 'code_here' SIGWINCH

Do something before every command

trap 'code_here' DEBUG

Do something when a shell function or a sourced file finishes executing

trap 'code_here' RETURN

PERFORMANCE

Disable Unicode

If 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=C

OBSOLETE SYNTAX

Shebang

Use #!/usr/bin/env bash instead of #!/bin/bash.

The former searches the user’s PATH to find the bash binary.
The latter assumes it is always installed to /bin/ which can cause issues.

NOTE: There are times when one may have a good reason for using #!/bin/bash or another direct path to the binary.

# Right:

    #!/usr/bin/env bash

# Less right:

    #!/bin/bash

Command Substitution

Use $() instead of .

# Right.
var="$(command)"

# Wrong.
var=`command`

# $() can easily be nested whereas `` cannot.
var="$(command "$(command)")"

Function Declaration

Do not use the function keyword, it reduces compatibility with older versions of bash.

# Right.
do_something() {
    # ...
}

# Wrong.
function do_something() {
    # ...
}

INTERNAL VARIABLES

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 OperatingSystems 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"

Get a pseudorandom integer

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"

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 becalled.

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

CONVERSION

Convert a hex color to RGB

Example 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"
255 255 255

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

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
# 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

Shorter `if` syntax

# 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
    # ...
}

Simpler `case` statement to set variable

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="$_"

OTHER

Use `read` as an alternative to the `sleep` command

Surprisingly, sleep is an external command and not a bash built-in.

CAVEAT: Requires bash 4+

Example Function:

read_sleep() {
    # Usage: read_sleep 1
    #        read_sleep 0.2
    read -rt "$1" <> <(:) || :
}

Example Usage:

read_sleep 1
read_sleep 0.1
read_sleep 30

For performance-critical situations, where it is not economic to open and close an excessive number of file descriptors, the allocation of a file descriptor may be done only once for all invocations of read:

(See the generic original implementation at https://blog.dhampir.no/content/sleeping-without-a-subprocess-in-bash-and-how-to-sleep-forever)

exec {sleep_fd}<> <(:)
while some_quick_test; do
    # equivalent of sleep 0.001
    read -t 0.001 -u $sleep_fd
done

Check if a program is in the user’s PATH

# 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
fi

Get the current date using `strftime`

Bash’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 AM

Get the username of the current user

CAVEAT: Requires bash 4.4+

$ : \\u
# Expand the parameter as if it were a prompt string.
$ printf '%s\n' "${_@P}"
black

Generate a UUID V4

CAVEAT: 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
d5b6c731-1310-4c24-9fe3-55d556d44374

Progress bars

This is a simple way of drawing progress bars without needing a for loopin 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 the list of functions in a script

get_functions() {
    # Usage: get_functions
    IFS=$'\n' read -d "" -ra functions < <(declare -F)
    printf '%s\n' "${functions[@]//declare -f }"
}

Bypass shell aliases

# alias
ls

# command
# shellcheck disable=SC1001
\ls

Bypass shell functions

# function
ls

# command
command ls

后台运行命令

This 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 background

AFTERWORD

Thanks 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!

字符串#

字符串包含#

字符串开始#

字符串结尾#

循环#

数字范围循环#

变量循环#

数组遍历#

索引遍历#

文件或者目录遍历#

文件处理#

将文件读取为字符串#

将文件按行读取成数组#

获取文件头部的 N 行#

获取尾部 N 行#

获取文件行数#

计算文件或者文件夹数量#

创建临时文件#

在两个标记之间抽取 N 行#

文件路径#

获取文件的目录#

获取文件路径的 base-name#

变量#

变量声明和使用#

基于变量命名变量#

ESCAPE SEQUENCES#

文本颜色#

文本属性#

光标移动#

文本擦除#

参数展开#

指令#

替换#

长度#

展开#

大小写修改#

默认值#

大括号展开#

范围#

字符串列表#

条件表达式#

文件条件判断#

文件比较#

变量测试#

变量比较#

算数操作#

赋值#

算数#

位操作#

逻辑#

Miscellaneous#

ARITHMETIC#

Simpler syntax to set variables#

Ternary Tests#

TRAPS#

Do something on script exit#

Ignore terminal interrupt (CTRL+C, SIGINT)#

React to window resize#

Do something before every command#

Do something when a shell function or a sourced file finishes executing#

PERFORMANCE#

Disable Unicode#

OBSOLETE SYNTAX#

Shebang#

Command Substitution#

Function Declaration#

INTERNAL VARIABLES#

Get the location to the bash binary#

Get the version of the current running bash process#

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 a pseudorandom integer#

INFORMATION ABOUT THE TERMINAL#

Get the terminal size in lines and columns (from a script)#

Get the terminal size in pixels#

字符串

字符串包含

字符串开始

字符串结尾

循环

数字范围循环

变量循环

数组遍历

索引遍历

文件或者目录遍历

文件处理

将文件读取为字符串

将文件按行读取成数组

获取文件头部的 N 行

获取尾部 N 行

获取文件行数

计算文件或者文件夹数量

创建临时文件

在两个标记之间抽取 N 行

文件路径

获取文件的目录

获取文件路径的 base-name

变量

变量声明和使用

基于变量命名变量

ESCAPE SEQUENCES

文本颜色

文本属性

光标移动

文本擦除

参数展开

指令

替换

长度

展开

大小写修改

默认值

大括号展开

范围

字符串列表

条件表达式

文件条件判断

文件比较

变量测试

变量比较

算数操作

赋值

算数

位操作

逻辑

Miscellaneous

ARITHMETIC

Simpler syntax to set variables

Ternary Tests

TRAPS

Do something on script exit

Ignore terminal interrupt (CTRL+C, SIGINT)

React to window resize

Do something before every command

Do something when a shell function or a sourced file finishes executing

PERFORMANCE

Disable Unicode

OBSOLETE SYNTAX

Shebang

Command Substitution

Function Declaration

INTERNAL VARIABLES

Get the location to the `bash` binary

Get the version of the current running `bash` process

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 a pseudorandom integer

INFORMATION ABOUT THE TERMINAL

Get the terminal size in lines and columns (from a script)

Get the terminal size in pixels