trim_string() {
    # Usage: trim_string "   example   string    "
    : "${1#"${1%%[![:space:]]*}"}"
    : "${_%"${_##*[![:space:]]}"}"
    printf '%s\n' "$_"
}

$ trim_string "    Hello,  World    "
Hello,  World

$ name="   John Black  "
$ trim_string "$name"
John Black

# shellcheck disable=SC2086,SC2048
trim_all() {
    # Usage: trim_all "   example   string    "
    set -f
    set -- $*
    printf '%s\n' "$*"
    set +f
}

$ trim_all "    Hello,    World    "
Hello, World

$ name="   John   Black  is     my    name.    "
$ trim_all "$name"
John Black is my name.

regex() {
    # Usage: regex "string" "regex"
    [[ $1 =~ $2 ]] && printf '%s\n' "${BASH_REMATCH[1]}"
}

$ # 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)

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() {
   # Usage: split "string" "delimiter"
   IFS=$'\n' read -d "" -ra arr <<< "${1//$2/$'\n'}"
   printf '%s\n' "${arr[@]}"
}

$ 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

lower() {
    # Usage: lower "string"
    printf '%s\n' "${1,,}"
}

$ lower "HELLO"
hello

$ lower "HeLlO"
hello

$ lower "hello"
hello

upper() {
    # Usage: upper "string"
    printf '%s\n' "${1^^}"
}

$ upper "hello"
HELLO

$ upper "HeLlO"
HELLO

$ upper "HELLO"
HELLO

reverse_case() {
    # Usage: reverse_case "string"
    printf '%s\n' "${1~~}"
}

$ reverse_case "hello"
HELLO

$ reverse_case "HeLlO"
hElLo

$ reverse_case "HELLO"
hello

trim_quotes() {
    # Usage: trim_quotes "string"
    : "${1//\'}"
    printf '%s\n' "${_//\"}"
}

$ var="'Hello', \"World\""
$ trim_quotes "$var"
Hello, World

strip_all() {
    # Usage: strip_all "string" "pattern"
    printf '%s\n' "${1//$2}"
}

$ 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() {
    # Usage: strip "string" "pattern"
    printf '%s\n' "${1/$2}"
}

$ strip "The Quick Brown Fox" "[aeiou]"
Th Quick Brown Fox

$ strip "The Quick Brown Fox" "[[:space:]]"
TheQuick Brown Fox

lstrip() {
    # Usage: lstrip "string" "pattern"
    printf '%s\n' "${1##$2}"
}

$ lstrip "The Quick Brown Fox" "The "
Quick Brown Fox

rstrip() {
    # Usage: rstrip "string" "pattern"
    printf '%s\n' "${1%%$2}"
}

$ rstrip "The Quick Brown Fox" " Fox"
The Quick Brown

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'
}

$ urlencode "https://github.com/dylanaraps/pure-bash-bible"
https%3A%2F%2Fgithub.com%2Fdylanaraps%2Fpure-bash-bible

urldecode() {
    # Usage: urldecode "string"
    : "${1//+/ }"
    printf '%b\n' "${_//%/\\x}"
}

$ urldecode "https%3A%2F%2Fgithub.com%2Fdylanaraps%2Fpure-bash-bible"
https://github.com/dylanaraps/pure-bash-bible

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

case "$var" in
    *sub_string*)
        # Do stuff
    ;;

    *sub_string2*)
        # Do more stuff
    ;;

    *)
        # Else
    ;;
esac

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

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

reverse_array() {
    # Usage: reverse_array "array"
    shopt -s extdebug
    f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@"
    shopt -u extdebug
}

$ reverse_array 1 2 3 4 5
5
4
3
2
1

$ arr=(red blue green)
$ reverse_array "${arr[@]}"
green
blue
red

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[@]}"
}

$ 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() {
    # Usage: random_array_element "array"
    local arr=("$@")
    printf '%s\n' "${arr[RANDOM % $#]}"
}

$ 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

arr=(a b c d)

cycle() {
    printf '%s ' "${arr[${i:=0}]}"
    ((i=i>=${#arr[@]}-1?0:++i))
}

arr=(true false)

cycle() {
    printf '%s ' "${arr[${i:=0}]}"
    ((i=i>=${#arr[@]}-1?0:++i))
}

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

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

arr=(apples oranges tomatoes)

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

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

while read -r line; do
    printf '%s\n' "$line"
done < "file"

# 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

file_data="$(<"file")"

# 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"

head() {
    # Usage: head "n" "file"
    mapfile -tn "$1" line < "$2"
    printf '%s\n' "${line[@]}"
}

$ head 2 ~/.bashrc
# Prompt
PS1='➜ '

$ head 1 ~/.bashrc
# Prompt

tail() {
    # Usage: tail "n" "file"
    mapfile -tn 0 line < "$2"
    printf '%s\n' "${line[@]: -$1}"
}

$ tail 2 ~/.bashrc
# Enable tmux.
# [[ -z "$TMUX"  ]] && exec tmux

$ tail 1 ~/.bashrc
# [[ -z "$TMUX"  ]] && exec tmux

lines() {
    # Usage: lines "file"
    mapfile -tn 0 lines < "$1"
    printf '%s\n' "${#lines[@]}"
}

lines_loop() {
    # Usage: lines_loop "file"
    count=0
    while IFS= read -r _; do
        ((count++))
    done < "$1"
    printf '%s\n' "$count"
}

$ lines ~/.bashrc
48

$ lines_loop ~/.bashrc
48

count() {
    # Usage: count /path/to/dir/*
    #        count /path/to/dir/*/
    printf '%s\n' "$#"
}

# 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

# Shortest.
>file

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

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"
}

# Extract code blocks from MarkDown file.
$ extract ~/projects/pure-bash/README.md '```sh' '```'
# Output here...

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:-/}"
}

$ dirname ~/Pictures/Wallpapers/1.jpg
/home/black/Pictures/Wallpapers

$ dirname ~/Pictures/Downloads/
/home/black/Pictures

basename() {
    # Usage: basename "path" ["suffix"]
    local tmp

    tmp=${1%"${1##*[!/]}"}
    tmp=${tmp##*/}
    tmp=${tmp%"${2/"$tmp"}"}

    printf '%s\n' "${tmp:-/}"
}

$ 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}"
value

$ 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"
value

# 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}

# 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))

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

trap '' INT

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

trap 'code_here' DEBUG

trap 'code_here' RETURN

# Disable unicode.
LC_ALL=C
LANG=C

# Right:

    #!/usr/bin/env bash

# Less right:

    #!/bin/bash

# Right.
var="$(command)"

# Wrong.
var=`command`

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

# 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"

"$OSTYPE"

"$PWD"

"$SECONDS"

"$RANDOM"

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"
}

# Output: LINES COLUMNS
$ get_term_size
15 55

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]}"
}

# Output: WIDTHxHEIGHT
$ get_window_size
1200x800

# Output (fail):
$ get_window_size
x

get_cursor_pos() {
    # Usage: get_cursor_pos
    IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
    printf '%s\n' "$x $y"
}

# Output: X Y
$ get_cursor_pos
1 8

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"
}

$ hex_to_rgb "#FFFFFF"
255 255 255

rgb_to_hex() {
    # Usage: rgb_to_hex "r" "g" "b"
    printf '#%02x%02x%02x\n' "$1" "$2" "$3"
}

$ 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
    # ...
}

# 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="$_"

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

read_sleep 1
read_sleep 0.1
read_sleep 30

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

# 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

date() {
    # Usage: date "format"
    # See: 'man strftime' for format.
    printf "%($1)T\\n" "-1"
}

# 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

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

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'
}

$ uuid
d5b6c731-1310-4c24-9fe3-55d556d44374

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}]"
}

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 ls

bkr() {
    (nohup "$@" &>/dev/null &)
}

bkr ./some_script.sh # some_script.sh is now running in the background

to_upper() {
  local -n ptr=${1}

  ptr=${ptr^^}
}

foo="bar"
to_upper foo
printf "%s\n" "${foo}" # BAR