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](https://github.com/dylanaraps/neofetch),
[pxltrm](https://github.com/dylanaraps/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](https://github.com/dylanaraps/pure-bash-bible/blob/master/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](#strings)
* [Trim leading and trailing white-space from string.](#trim-leading-and-trailing-white-space-from-string)
* [Trim all white-space from string and truncate spaces.](#trim-all-white-space-from-string-and-truncate-spaces)
* [Use REGEX on a string.](#use-regex-on-a-string)
* [Split a string on a delimiter.](#split-a-string-on-a-delimiter)
* [Change a string to lowercase.](#change-a-string-to-lowercase)
* [Change a string to uppercase.](#change-a-string-to-uppercase)
* [Trim quotes from a string.](#trim-quotes-from-a-string)
* [Strip all instances of pattern from string.](#strip-all-instances-of-pattern-from-string)
* [Strip first occurrence of pattern from string.](#strip-first-occurrence-of-pattern-from-string)
* [Strip pattern from start of string.](#strip-pattern-from-start-of-string)
* [Strip pattern from end of string.](#strip-pattern-from-end-of-string)
* [Check if string contains a sub-string.](#check-if-string-contains-a-sub-string)
* [Check if string starts with sub-string.](#check-if-string-starts-with-sub-string)
* [Check if string ends with sub-string.](#check-if-string-ends-with-sub-string)
* [Variables](#variables)
* [Assign and access a variable using a variable.](#assign-and-access-a-variable-using-a-variable)
* [Indirection](#indirection)
* [Replacement](#replacement)
* [Length](#length)
* [Expansion](#expansion)
* [Case Modification](#case-modification)
* [Default Value](#default-value)
* [Arrays](#arrays)
* [Reverse an array.](#reverse-an-array)
* [Remove duplicate array elements.](#remove-duplicate-array-elements)
* [Cycle through an array.](#cycle-through-an-array)
* [Toggle between two values.](#toggle-between-two-values)
* [Loops](#loops)
* [Loop over a range of numbers.](#loop-over-a-range-of-numbers)
* [Loop over a variable range of numbers.](#loop-over-a-variable-range-of-numbers)
* [Loop over an array.](#loop-over-an-array)
* [Loop over an array with an index.](#loop-over-an-array-with-an-index)
* [Loop over the contents of a file.](#loop-over-the-contents-of-a-file)
* [Loop over files and directories.](#loop-over-files-and-directories)
* [File handling](#file-handling)
* [Read a file to a string.](#read-a-file-to-a-string)
* [Read a file to an array (*by line*).](#read-a-file-to-an-array-by-line)
* [Get the first N lines of a file.](#get-the-first-n-lines-of-a-file)
* [Get the last N lines of a file.](#get-the-last-n-lines-of-a-file)
* [Get the number of lines in a file.](#get-the-number-of-lines-in-a-file)
* [Count files or directories in directory.](#count-files-or-directories-in-directory)
* [Create an empty file.](#create-an-empty-file)
* [Extract lines between two markers.](#extract-lines-between-two-markers)
* [File Paths](#file-paths)
* [Get the directory name of a file path.](#get-the-directory-name-of-a-file-path)
* [Get the base-name of a file path.](#get-the-base-name-of-a-file-path)
* [Arithmetic](#arithmetic)
* [Simpler syntax to set variables.](#simpler-syntax-to-set-variables)
* [Ternary tests.](#ternary-tests)
* [Brace Expansion](#brace-expansion)
* [Ranges](#ranges)
* [String Lists](#string-lists)
* [Obsolete Syntax](#obsolete-syntax)
* [Shebang.](#shebang)
* [Command Substitution.](#command-substitution)
* [Function Declaration.](#function-declaration)
* [Internal Variables](#internal-variables)
* [Get the location to the `bash` binary.](#get-the-location-to-the-bash-binary)
* [Get the version of the current running `bash` process.](#get-the-version-of-the-current-running-bash-process)
* [Open the user's preferred text editor.](#open-the-users-preferred-text-editor)
* [Get the name of the current function.](#get-the-name-of-the-current-function)
* [Get the host-name of the system.](#get-the-host-name-of-the-system)
* [Get the architecture of the Operating System.](#get-the-architecture-of-the-operating-system)
* [Get the name of the Operating System / Kernel.](#get-the-name-of-the-operating-system--kernel)
* [Get the current working directory.](#get-the-current-working-directory)
* [Get the number of seconds the script has been running.](#get-the-number-of-seconds-the-script-has-been-running)
* [Information about the terminal](#information-about-the-terminal)
* [Get the terminal size in lines and columns (*from a script*).](#get-the-terminal-size-in-lines-and-columns-from-a-script)
* [Get the terminal size in pixels.](#get-the-terminal-size-in-pixels)
* [Get the current cursor position.](#get-the-current-cursor-position)
* [Escape Sequences](#escape-sequences)
* [Text Colors.](#text-colors)
* [Text Attributes.](#text-attributes)
* [Colors](#colors)
* [Convert a hex color to RGB.](#convert-a-hex-color-to-rgb)
* [Convert an RGB color to hex.](#convert-an-rgb-color-to-hex)
* [Code Golf](#code-golf)
* [Shorter `for` loop syntax.](#shorter-for-loop-syntax)
* [Shorter infinite loops.](#shorter-infinite-loops)
* [Shorter function declaration.](#shorter-function-declaration)
* [Shorter `if` syntax.](#shorter-if-syntax)
* [Simpler `case` statement to set variable.](#simpler-case-statement-to-set-variable)
* [Other](#other)
* [Use `read` as an alternative to the `sleep` command.](#use-read-as-an-alternative-to-the-sleep-command)
* [Check if a program is in the user's PATH.](#check-if-a-program-is-in-the-users-path)
* [Get the current date using `strftime`.](#get-the-current-date-using-strftime)
* [Progress bars.](#progress-bars)
* [Get the list of functions from your script.](#get-the-list-of-functions-from-your-script)
* [Bypass shell aliases.](#bypass-shell-aliases)
* [Bypass shell functions.](#bypass-shell-functions)
# 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:**
```sh
trim_string() {
# Usage: trim_string " example string "
: "${1#"${1%%[![:space:]]*}"}"
: "${_%"${_##*[![:space:]]}"}"
printf '%s\n' "$_"
}
```
**Example Usage:**
```shell
$ 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:**
```sh
# shellcheck disable=SC2086,SC2048
trim_all() {
# Usage: trim_all " example string "
set -f
set -- $*
printf '%s\n' "$*"
set +f
}
```
**Example Usage:**
```shell
$ 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:**
```sh
regex() {
# Usage: regex "string" "regex"
[[ $1 =~ $2 ]] && printf '%s\n' "${BASH_REMATCH[1]}"
}
```
**Example Usage:**
```shell
$ # 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:**
```shell
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.
```shell
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:**
```sh
lower() {
# Usage: lower "string"
printf '%s\n' "${1,,}"
}
```
**Example Usage:**
```shell
$ lower "HELLO"
hello
$ lower "HeLlO"
hello
$ lower "hello"
hello
```
## Change a string to uppercase.
**CAVEAT:** Requires `bash` 4+
**Example Function:**
```sh
upper() {
# Usage: upper "string"
printf '%s\n' "${1^^}"
}
```
**Example Usage:**
```shell
$ upper "hello"
HELLO
$ upper "HeLlO"
HELLO
$ upper "HELLO"
HELLO
```
## Trim quotes from a string.
**Example Function:**
```sh
trim_quotes() {
# Usage: trim_quotes "string"
: "${1//\'}"
printf "%s\\n" "${_//\"}"
}
```
**Example Usage:**
```shell
$ var="'Hello', \"World\""
$ trim_quotes "$var"
Hello, World
```
## Strip all instances of pattern from string.
**Example Function:**
```sh
strip_all() {
# Usage: strip_all "string" "pattern"
printf '%s\n' "${1//$2}"
}
```
**Example Usage:**
```shell
$ 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:**
```sh
strip() {
# Usage: strip "string" "pattern"
printf '%s\n' "${1/$2}"
}
```
**Example Usage:**
```shell
$ 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:**
```sh
lstrip() {
# Usage: lstrip "string" "pattern"
printf '%s\n' "${1##$2}"
}
```
**Example Usage:**
```shell
$ lstrip "The Quick Brown Fox" "The "
Quick Brown Fox
```
## Strip pattern from end of string.
**Example Function:**
```sh
rstrip() {
# Usage: rstrip "string" "pattern"
printf '%s\n' "${1%%$2}"
}
```
**Example Usage:**
```shell
$ rstrip "The Quick Brown Fox" " Fox"
The Quick Brown
```
## Check if string contains a sub-string.
**Using a test:**
```shell
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 [[ "${arr[*]}" == *sub_string* ]]; then
printf '%s\n' "sub_string is in array."
fi
```
## Check if string starts with sub-string.
```shell
if [[ "$var" == sub_string* ]]; then
printf '%s\n' "var starts with sub_string."
fi
# Inverse (var doesn't start with sub_string).
if [[ "$var" != sub_string* ]]; then
printf '%s\n' "var does not start with sub_string."
fi
```
## Check if string ends with sub-string.
```shell
if [[ "$var" == *sub_string ]]; then
printf '%s\n' "var ends with sub_string."
fi
# Inverse (var doesn't start with sub_string).
if [[ "$var" != *sub_string ]]; then
printf '%s\n' "var does not end with sub_string."
fi
```
**Using a case statement:**
```shell
case "$var" in
*sub_string*)
# Do stuff
;;
*sub_string2*)
# Do more stuff
;;
*)
# Else
;;
esac
```
# Variables
## Assign and access a variable using a variable.
```shell
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' "${!var2}"
```
## Indirection
| Parameter | What does it do? |
| --------- | ---------------- |
| `${!VAR}` | Access a variable based on the value of `VAR`. See: [link](#assign-and-access-a-variable-using-a-variable)
| `${!VAR*}` | Expand to `IFS` separated list of variable names starting with `VAR`. |
| `${!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.
| `${VAR:OFFSET:-OFFSET}` | Cut first `N` chars and last `N` chars. | `bash 4.2+` |
## Case Modification
| Parameter | What does it do? | CAVEAT |
| --------- | ---------------- | ------ |
| `${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.
| `${VAR?STRING}` | Display an error if unset.
# Arrays
## Reverse an array.
Enabling `extdebug` allows access to the `BASH_ARGV` array which stores
the current function’s arguments in reverse.
**Example Function:**
```sh
reverse_array() {
# Usage: reverse_array "array"
shopt -s extdebug
f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@"
shopt -u extdebug
}
```
**Example Usage:**
```shell
$ reverse_array 1 2 3 4 5
5
4
3
2
1
$ arr=(red blue green)
$ reverse_array "${arr[@]}"
green
blue
red
```
## Remove duplicate array elements.
Create a temporary associative array. When setting associative array
values and a duplicate assignment occurs, bash overwrites the key. This
allows us to effectively remove array duplicates.
**CAVEAT:** Requires `bash` 4+
**Example Function:**
```sh
remove_array_dups() {
# Usage: remove_array_dups "array"
declare -A tmp_array
for i in "$@"; do
[[ "$i" ]] && IFS=" " tmp_array["${i:- }"]=1
done
printf '%s\n' "${!tmp_array[@]}"
}
```
**Example Usage:**
```shell
$ 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 "${arr[@]}"
red
green
blue
```
## Cycle through an array.
Each time the `printf` is called, the next array element is printed. When
the print hits the last array element it starts from the first element
again.
```sh
arr=(a b c d)
cycle() {
printf '%s ' "${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.
```sh
arr=(true false)
cycle() {
printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
}
```
# Loops
## Loop over a range of numbers.
Don't use `seq`.
```shell
# Loop from 0-100 (no variable support).
for i in {0..100}; do
printf '%s\n' "$i"
done
```
## Loop over a variable range of numbers.
Don't use `seq`.
```shell
# Loop from 0-VAR.
VAR=50
for ((i=0;i<=VAR;i++)); do
printf '%s\n' "$i"
done
```
## Loop over an array.
```shell
arr=(apples oranges tomatoes)
# Just elements.
for element in "${arr[@]}"; do
printf '%s\n' "$element"
done
```
## Loop over an array with an index.
```shell
arr=(apples oranges tomatoes)
# Elements and index.
for i in "${!arr[@]}"; do
printf '%s\n' "${arr[$i]}"
done
# Alternative method.
for ((i=0;i<${#arr[@]};i++)); do
printf '%s\n' "${arr[$i]}"
done
```
## Loop over the contents of a file.
```shell
while read -r line; do
printf '%s\n' "$line"
done < "file"
```
## Loop over files and directories.
Don’t use `ls`.
```shell
# 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' "$file"
done
shopt -u globstar
```
# File handling
**CAVEAT:** `bash` doesn't handle binary data properly in versions `< 4.4`.
## Read a file to a string.
Alternative to the `cat` command.
```shell
file_data="$(<"file")"
```
## Read a file to an array (*by line*).
Alternative to the `cat` command.
```shell
# 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:**
```sh
head() {
# Usage: head "n" "file"
mapfile -tn "$1" line < "$2"
printf '%s\n' "${line[@]}"
}
```
**Example Usage:**
```shell
$ 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:**
```sh
tail() {
# Usage: tail "n" "file"
mapfile -tn 0 line < "$2"
printf '%s\n' "${line[@]: -$1}"
}
```
**Example Usage:**
```shell
$ 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):**
```sh
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.
```sh
lines_loop() {
# Usage: lines_loop "file"
count=0
while IFS= read -r _; do
((count++))
done < "$1"
printf '%s\n' "$count"
}
```
**Example Usage:**
```shell
$ 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:**
```sh
count() {
# Usage: count /path/to/dir/*
# count /path/to/dir/*/
printf '%s\n' "$#"
}
```
**Example Usage:**
```shell
# 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`.
```shell
# Shortest.
:> file
# Longer alternatives:
echo -n > file
printf '' > file
```
## Extract lines between two markers.
**Example Function:**
```sh
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:**
```shell
# 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:**
```sh
dirname() {
# Usage: dirname "path"
printf '%s\n' "${1%/*}/"
}
```
**Example Usage:**
```shell
$ 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:**
```sh
basename() {
# Usage: basename "path"
: "${1%/}"
printf '%s\n' "${_##*/}"
}
```
**Example Usage:**
```shell
$ basename ~/Pictures/Wallpapers/1.jpg
1.jpg
$ basename ~/Pictures/Downloads/
Downloads
```
# Arithmetic
## Simpler syntax to set variables.
```shell
# Simple math
((var=1+2))
# Decrement/Increment variable
((var++))
((var--))
((var+=1))
((var-=1))
# Using variables
((var=var2*arr[2]))
```
## Ternary tests.
```shell
# 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))
```
# Brace Expansion
## Ranges
```shell
# Syntax: {..}
# 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: {....}
# CAVEAT: bash 4+
echo {1..10..2} # Increment by 2.
```
## String Lists
```shell
echo {apples,oranges,pears,grapes}
# Example Usage:
# Remove dirs Movies, Music and ISOS from ~/Downloads/.
rm -rf ~/Downloads/{Movies,Music,ISOS}
```
# 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.
```shell
# Right:
#!/usr/bin/env bash
# Wrong:
#!/bin/bash
```
## Command Substitution.
Use `$()` instead of `` ` ` ``.
```shell
# Right.
var="$(command)"
# Wrong.
var=`command`
# $() can easily be nested whereas `` cannot.
var="$(command "$(command)")"
```
## Function Declaration.
Don't use the `function` keyword, it reduces compatibility with older versions of `bash`.
```shell
# Right.
do_something() {
# ...
}
# Wrong.
function do_something() {
# ...
}
```
# Internal Variables
**NOTE**: This list does not include every internal variable (*You can
help by adding a missing entry!*).
For a complete list, see:
http://tldp.org/LDP/abs/html/internalvariables.html
## Get the location to the `bash` binary.
```shell
"$BASH"
```
## Get the version of the current running `bash` process.
```shell
# As a string.
"$BASH_VERSION"
# As an array.
"${BASH_VERSINFO[@]}"
```
## Open the user's preferred text editor.
```shell
"$EDITOR" "$file"
# NOTE: This variable may be empty, set a fallback value.
"${EDITOR:-vi}" "$file"
```
## Get the name of the current function.
```shell
# Current function.
"${FUNCNAME[0]}"
# Parent function.
"${FUNCNAME[1]}"
# So on and so forth.
"${FUNCNAME[2]}"
"${FUNCNAME[3]}"
# All functions including parents.
"${FUNCNAME[@]}"
```
## Get the host-name of the system.
```shell
"$HOSTNAME"
# NOTE: This variable may be empty.
# Optionally set a fallback to the hostname command.
"${HOSTNAME:-$(hostname)}"
```
## Get the architecture of the Operating System.
```shell
"$HOSTTYPE"
```
## Get the name of the Operating System / Kernel.
This can be used to add conditional support for different Operating
Systems without needing to call `uname`.
```shell
"$OSTYPE"
```
## Get the current working directory.
This is an alternative to the `pwd` built-in.
```shell
"$PWD"
```
## Get the number of seconds the script has been running.
```shell
"$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:**
```sh
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:**
```shell
# 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:**
```sh
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:**
```shell
# 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:**
```sh
get_cursor_pos() {
# Usage: get_cursor_pos
IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
printf '%s\n' "$x $y"
}
```
**Example Usage:**
```shell
# Output: X Y
$ get_cursor_pos
1 8
```
# 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.
| Sequence | What does it do? | Value |
| -------- | ---------------- | ----- |
| `\e[38;5;m` | Set text foreground color. | `0-255`
| `\e[48;5;m` | Set text background color. | `0-255`
| `\e[38;2;;;m` | Set text foreground color to RGB color. | `R`, `G`, `B`
| `\e[48;2;;;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[5m` | Slow blink. |
| `\e[7m` | Swap foreground and background colors. |
# Colors
## Convert a hex color to RGB.
**Example Function:**
```sh
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:**
```shell
$ hex_to_rgb "#FFFFFF"
255 255 255
```
## Convert an RGB color to hex.
**Example Function:**
```sh
rgb_to_hex() {
# Usage: rgb_to_hex "r" "g" "b"
printf '#%02x%02x%02x\n' "$1" "$2" "$3"
}
```
**Example Usage:**
```shell
$ rgb_to_hex "255" "255" "255"
#FFFFFF
```
# Code Golf
## Shorter `for` loop syntax.
```shell
# 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.
```shell
# Normal method
while :; do echo hi; done
# Shorter
for((;;)){ echo hi;}
```
## Shorter function declaration.
```shell
# 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 "$i"; done
```
## Shorter `if` syntax.
```shell
# One line
# Note: The 3rd statement may run when the 1st is true
[[ "$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.
```shell
# 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:**
```sh
read_sleep() {
# Usage: sleep 1
# sleep 0.2
read -rst "${1:-1}" -N 999
}
```
**Example Usage:**
```shell
read_sleep 1
read_sleep 0.1
read_sleep 30
```
## Check if a program is in the user's PATH.
```shell
# 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:**
```sh
date() {
# Usage: date "format"
# See: 'man strftime' for format.
printf "%($1)T\\n" "-1"
}
```
**Example Usage:**
```shell
# 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
```
## Progress bars.
This is a simple way of drawing progress bars without needing a for loop
in the function itself.
**Example Function:**
```sh
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// /-}${total}]"
}
```
**Example Usage:**
```shell
for ((i=0;i<=100;i++)); do
# Pure bash micro sleeps (for the example).
(:;:) && (:;:) && (:;:) && (:;:) && (:;:)
# Print the bar.
bar "$i" "10"
done
printf '\n'
```
## Get the list of functions from your script.
```sh
get_functions() {
# Usage: get_functions
IFS=$'\n' read -d "" -ra functions < <(declare -F)
printf '%s\n' "${functions[@]//declare -f }"
}
```
## Bypass shell aliases.
```shell
# alias
ls
# command
# shellcheck disable=SC1001
\ls
```
## Bypass shell functions.
```shell
# function
ls
# command
command ls
```