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📖 A collection of pure bash alternatives to external processes.

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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.

Any donations are appreciated, they give me the time to make this the best resource possible.


Table of Contents


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

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

Random array element.

Example Function:

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

Example Usage:

$ array=(red green blue yellow brown)
$ random_array_element "${array[@]}"
yellow

# You can also just pass multiple arguments.
$ random_array_element 1 2 3 4 5 6 7
3

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

# 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 handling

CAVEAT: bash doesn't handle binary data properly in versions < 4.4.

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.

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 it's more compatible but it's 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

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

Extract lines between two markers.

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...

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

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}"

Escape Sequences

Contrary to popular belief, there's no issue in using raw escape sequences. Using tput just abstracts the same ANSI escape sequences. What's worse is that tput isn't actually portable, there are a number of different tput variants on different Operating Systems each with different commands (try and run tput setaf 3 on a FreeBSD system). The easiest solution ends up being raw ANSI sequences.

Text Colors.

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

Text Attributes.

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 Slow blink.
\e[7m Swap foreground and background colors.

Cursor Movement.

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.

Erasing Text.

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.

Parameter Expansion.

Indirection

Parameter What does it do?
${!VAR} Access a variable based on the value of VAR. See: link
${!VAR*} Expand to IFS separated list of variable names starting with VAR.
${!VAR@} Expand to IFS separated list of variable names starting with VAR.

Replacement

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.

Length

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

Expansion

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.

Case Modification

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+

Default Value

Parameter What does it do?
${VAR:-STRING} If VAR is empty or unset, use STRING as it's value.
${VAR-STRING} If VAR is unset, use STRING as it's 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 isn't empty, use STRING as it's value.
${VAR+STRING} If VAR is set, use STRING as it's value.
${VAR:?STRING} Display an error if empty or unset.
${VAR?STRING} Display an error if unset.

Brace Expansion

Ranges

# 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.

String Lists

echo {apples,oranges,pears,grapes}

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

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))

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.
# Right:

    #!/usr/bin/env bash

# Wrong:

    #!/bin/bash

Command Substitution.

Use $() instead of ` `.

# Right.
var="$(command)"

# Wrong.
var=`command`

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

Function Declaration.

Don't use the function keyword, it reduces compatibility with older versions of bash.

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

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

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"

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

Conversion

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

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
# 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.

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.

# 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.

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

Generate a UUID V4.

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 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 the list of functions from your 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

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📖 A collection of pure bash alternatives to external processes.

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