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Added build files to turn the bible into a book

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2018-06-20 12:40:31 +10:00
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4
README.md
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@@ -41,7 +41,6 @@ scripts and not full blown utilities.
<br> <br>
<!-- CHAPTER START -->
# Table of Contents # Table of Contents
<!-- vim-markdown-toc GFM --> <!-- vim-markdown-toc GFM -->
@@ -155,8 +154,6 @@ scripts and not full blown utilities.
<!-- vim-markdown-toc --> <!-- vim-markdown-toc -->
<!-- CHAPTER END -->
<br> <br>
<!-- CHAPTER START --> <!-- CHAPTER START -->
@@ -1864,7 +1861,6 @@ command ls
<!-- CHAPTER END --> <!-- CHAPTER END -->
<!-- CHAPTER START -->
# Afterword # 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! 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!

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manuscript/Book.txt
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@@ -15,5 +15,3 @@ chapter13.txt
chapter14.txt chapter14.txt
chapter15.txt chapter15.txt
chapter16.txt chapter16.txt
chapter17.txt
chapter18.txt

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manuscript/chapter0.txt
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@@ -1,115 +1,376 @@
# Table of Contents # Strings
<!-- vim-markdown-toc GFM --> ## Trim leading and trailing white-space from string
* [Strings](#strings) This is an alternative to `sed`, `awk`, `perl` and other tools. The
* [Trim leading and trailing white-space from string](#trim-leading-and-trailing-white-space-from-string) function below works by finding all leading and trailing white-space and
* [Trim all white-space from string and truncate spaces](#trim-all-white-space-from-string-and-truncate-spaces) removing it from the start and end of the string. The `:` built-in is used in place of a temporary variable.
* [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)
* [Arrays](#arrays)
* [Reverse an array](#reverse-an-array)
* [Remove duplicate array elements](#remove-duplicate-array-elements)
* [Random array element](#random-array-element)
* [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)
* [Variables](#variables)
* [Assign and access a variable using a variable](#assign-and-access-a-variable-using-a-variable)
* [Escape Sequences](#escape-sequences)
* [Text Colors](#text-colors)
* [Text Attributes](#text-attributes)
* [Cursor Movement](#cursor-movement)
* [Erasing Text](#erasing-text)
* [Parameter Expansion](#parameter-expansion)
* [Indirection](#indirection)
* [Replacement](#replacement)
* [Length](#length)
* [Expansion](#expansion)
* [Case Modification](#case-modification)
* [Default Value](#default-value)
* [Brace Expansion](#brace-expansion)
* [Ranges](#ranges)
* [String Lists](#string-lists)
* [Arithmetic](#arithmetic)
* [Simpler syntax to set variables](#simpler-syntax-to-set-variables)
* [Ternary tests](#ternary-tests)
* [Traps](#traps)
* [Do something on script exit](#do-something-on-script-exit)
* [Ignore terminal interrupt (CTRL+C, SIGINT)](#ignore-terminal-interrupt-ctrlc-sigint)
* [React to window resize.](#react-to-window-resize)
* [Do something before every command.](#do-something-before-every-command)
* [Do something when a shell function or a sourced file finishes executing](#do-something-when-a-shell-function-or-a-sourced-file-finishes-executing)
* [Performance](#performance)
* [Disable Unicode](#disable-unicode)
* [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)
* [Get a pseudorandom integer](#get-a-pseudorandom-integer)
* [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)
* [Conversion](#conversion)
* [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)
* [Generate a UUID V4](#generate-a-uuid-v4)
* [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)
* [Afterword](#afterword)
<!-- vim-markdown-toc --> **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.
**Example Function:**
```sh
split() {
# Usage: split "string" "delimiter"
IFS=$'\n' read -d "" -ra arr <<< "${1//$2/$'\n'}"
printf '%s\n' "${arr[@]}"
}
```
**Example Usage:**
```shell
$ 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
```
## 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 [[ "${arr[*]}" == *sub_string* ]]; then
printf '%s\n' "sub_string is in array."
fi
```
**Using a case statement:**
```shell
case "$var" in
*sub_string*)
# Do stuff
;;
*sub_string2*)
# Do more stuff
;;
*)
# Else
;;
esac
```
## 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
```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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# Strings # Arrays
## Trim leading and trailing white-space from string ## Reverse an array
This is an alternative to `sed`, `awk`, `perl` and other tools. The Enabling `extdebug` allows access to the `BASH_ARGV` array which stores
function below works by finding all leading and trailing white-space and the current function’s arguments in reverse.
removing it from the start and end of the string. The `:` built-in is used in place of a temporary variable.
**Example Function:** **Example Function:**
```sh ```sh
trim_string() { reverse_array() {
# Usage: trim_string " example string " # Usage: reverse_array "array"
: "${1#"${1%%[![:space:]]*}"}" shopt -s extdebug
: "${_%"${_##*[![:space:]]}"}" f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@"
printf '%s\n' "$_" shopt -u extdebug
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
$ trim_string " Hello, World " $ reverse_array 1 2 3 4 5
Hello, World 5
4
3
2
1
$ name=" John Black " $ arr=(red blue green)
$ trim_string "$name" $ reverse_array "${arr[@]}"
John Black green
blue
red
``` ```
## Remove duplicate array elements
## Trim all white-space from string and truncate spaces 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.
This is an alternative to `sed`, `awk`, `perl` and other tools. The **CAVEAT:** Requires `bash` 4+
function below works by abusing word splitting to create a new string
without leading/trailing white-space and with truncated spaces.
**Example Function:** **Example Function:**
```sh ```sh
# shellcheck disable=SC2086,SC2048 remove_array_dups() {
trim_all() { # Usage: remove_array_dups "array"
# Usage: trim_all " example string " declare -A tmp_array
set -f
set -- $* for i in "$@"; do
printf '%s\n' "$*" [[ "$i" ]] && IFS=" " tmp_array["${i:- }"]=1
set +f done
printf '%s\n' "${!tmp_array[@]}"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
$ trim_all " Hello, World " $ remove_array_dups 1 1 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5
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.
**Example Function:**
```sh
split() {
# Usage: split "string" "delimiter"
IFS=$'\n' read -d "" -ra arr <<< "${1//$2/$'\n'}"
printf '%s\n' "${arr[@]}"
}
```
**Example Usage:**
```shell
$ split "apples,oranges,pears,grapes" ","
apples
oranges
pears
grapes
$ split "1, 2, 3, 4, 5" ", "
1 1
2 2
3 3
4 4
5 5
# Multi char delimiters work too! $ arr=(red red green blue blue)
$ split "hello---world---my---name---is---john" "---" $ remove_array_dups "${arr[@]}"
hello red
world green
my blue
name
is
john
``` ```
## Change a string to lowercase ## Random array element
**CAVEAT:** Requires `bash` 4+
**Example Function:** **Example Function:**
```sh ```sh
lower() { random_array_element() {
# Usage: lower "string" # Usage: random_array_element "array"
printf '%s\n' "${1,,}" local arr=("$@")
printf '%s\n' "${arr[RANDOM % $#]}"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
$ lower "HELLO" $ array=(red green blue yellow brown)
hello $ random_array_element "${array[@]}"
yellow
$ lower "HeLlO" # You can also just pass multiple arguments.
hello $ random_array_element 1 2 3 4 5 6 7
3
$ lower "hello"
hello
``` ```
## Change a string to uppercase ## Cycle through an array
**CAVEAT:** Requires `bash` 4+ 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
**Example Function:** again.
```sh ```sh
upper() { arr=(a b c d)
# Usage: upper "string"
printf '%s\n' "${1^^}" cycle() {
printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
} }
``` ```
**Example Usage:**
```shell ## Toggle between two values
$ upper "hello"
HELLO
$ upper "HeLlO" This works the same as above, this is just a different use case.
HELLO
$ upper "HELLO"
HELLO
```
## Trim quotes from a string
**Example Function:**
```sh ```sh
trim_quotes() { arr=(true false)
# Usage: trim_quotes "string"
: "${1//\'}" cycle() {
printf '%s\n' "${_//\"}" printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
} }
``` ```
**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 [[ "${arr[*]}" == *sub_string* ]]; then
printf '%s\n' "sub_string is in array."
fi
```
**Using a case statement:**
```shell
case "$var" in
*sub_string*)
# Do stuff
;;
*sub_string2*)
# Do more stuff
;;
*)
# Else
;;
esac
```
## 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
```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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@@ -1,30 +1,42 @@
# Arithmetic # Traps
## Simpler syntax to set variables Traps allow you to execute code on various signals. In `pxltrm` I'm using traps to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit.
These `trap` lines should be added near the start of your script so any early errors are also caught.
**NOTE:** For a full list of signals, see `trap -l`.
## Do something on script exit
```shell ```shell
# Simple math # Clear screen on script exit.
((var=1+2)) trap 'printf \\e[2J\\e[H\\e[m' EXIT
# Decrement/Increment variable
((var++))
((var--))
((var+=1))
((var-=1))
# Using variables
((var=var2*arr[2]))
``` ```
## Ternary tests ## Ignore terminal interrupt (CTRL+C, SIGINT)
```shell ```shell
# Set the value of var to var2 if var2 is greater than var. trap '' INT
# var: variable to set. ```
# var2>var: Condition to test.
# ?var2: If the test succeeds. ## React to window resize.
# :var: If the test fails.
((var=var2>var?var2:var)) ```shell
# Call a function on window resize.
trap 'code_here' SIGWINCH
```
## Do something before every command.
```shell
trap 'code_here' DEBUG
```
## Do something when a shell function or a sourced file finishes executing
```shell
trap 'code_here' RETURN
``` ```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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@@ -1,42 +1,13 @@
# Traps # Performance
Traps allow you to execute code on various signals. In `pxltrm` I'm using traps to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit. ## Disable Unicode
These `trap` lines should be added near the start of your script so any early errors are also caught. If your script doesn't require unicode, you can disable it for a speed boost. Results may vary but I've seen an improvement in Neofetch and some other smaller programs.
**NOTE:** For a full list of signals, see `trap -l`.
## Do something on script exit
```shell ```shell
# Clear screen on script exit. # Disable unicode.
trap 'printf \\e[2J\\e[H\\e[m' EXIT LC_ALL=C
``` LANG=C
## Ignore terminal interrupt (CTRL+C, SIGINT)
```shell
trap '' INT
```
## React to window resize.
```shell
# Call a function on window resize.
trap 'code_here' SIGWINCH
```
## Do something before every command.
```shell
trap 'code_here' DEBUG
```
## Do something when a shell function or a sourced file finishes executing
```shell
trap 'code_here' RETURN
``` ```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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@@ -1,13 +1,51 @@
# Performance # Obsolete Syntax
## Disable Unicode ## Shebang
If your script doesn't require unicode, you can disable it for a speed boost. Results may vary but I've seen an improvement in Neofetch and some other smaller programs. 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 ```shell
# Disable unicode. # Right:
LC_ALL=C
LANG=C #!/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() {
# ...
}
``` ```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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@@ -1,51 +1,99 @@
# Obsolete Syntax # Internal Variables
## Shebang **NOTE**: This list does not include every internal variable (*You can
help by adding a missing entry!*).
Use `#!/usr/bin/env bash` instead of `#!/bin/bash`. For a complete list, see:
http://tldp.org/LDP/abs/html/internalvariables.html
- The former searches the user's `PATH` to find the `bash` binary. ## Get the location to the `bash` binary
- The latter assumes it is always installed to `/bin/` which can cause issues.
```shell ```shell
# Right: "$BASH"
#!/usr/bin/env bash
# Wrong:
#!/bin/bash
``` ```
## Command Substitution ## Get the version of the current running `bash` process
Use `$()` instead of `` ` ` ``.
```shell ```shell
# Right. # As a string.
var="$(command)" "$BASH_VERSION"
# Wrong. # As an array.
var=`command` "${BASH_VERSINFO[@]}"
# $() can easily be nested whereas `` cannot.
var="$(command "$(command)")"
``` ```
## Function Declaration ## Open the user's preferred text editor
Don't use the `function` keyword, it reduces compatibility with older versions of `bash`.
```shell ```shell
# Right. "$EDITOR" "$file"
do_something() {
# ...
}
# Wrong. # NOTE: This variable may be empty, set a fallback value.
function do_something() { "${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
"$SECONDS"
```
## Get a pseudorandom integer
Each time `$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*).
```shell
"$RANDOM"
``` ```
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@@ -1,99 +1,78 @@
# Internal Variables # Information about the terminal
**NOTE**: This list does not include every internal variable (*You can ## Get the terminal size in lines and columns (*from a script*)
help by adding a missing entry!*).
For a complete list, see: This is handy when writing scripts in pure bash and `stty`/`tput` can’t be
http://tldp.org/LDP/abs/html/internalvariables.html called.
## Get the location to the `bash` binary **Example Function:**
```shell ```sh
"$BASH" 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 $COLUMNS"
}
``` ```
## Get the version of the current running `bash` process **Example Usage:**
```shell ```shell
# As a string. # Output: LINES COLUMNS
"$BASH_VERSION" $ get_term_size
15 55
# As an array.
"${BASH_VERSINFO[@]}"
``` ```
## Open the user's preferred text editor ## Get the terminal size in pixels
```shell **CAVEAT**: This does not work in some terminal emulators.
"$EDITOR" "$file"
# NOTE: This variable may be empty, set a fallback value. **Example Function:**
"${EDITOR:-vi}" "$file"
```sh
get_window_size() {
# Usage: get_window_size
printf '%b' "${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${term_size[2]}"
}
``` ```
## Get the name of the current function **Example Usage:**
```shell ```shell
# Current function. # Output: WIDTHxHEIGHT
"${FUNCNAME[0]}" $ get_window_size
1200x800
# Parent function. # Output (fail):
"${FUNCNAME[1]}" $ get_window_size
x
# So on and so forth.
"${FUNCNAME[2]}"
"${FUNCNAME[3]}"
# All functions including parents.
"${FUNCNAME[@]}"
``` ```
## Get the host-name of the system ## Get the current cursor position
```shell This is useful when creating a TUI in pure bash.
"$HOSTNAME"
# NOTE: This variable may be empty. **Example Function:**
# Optionally set a fallback to the hostname command.
"${HOSTNAME:-$(hostname)}" ```sh
get_cursor_pos() {
# Usage: get_cursor_pos
IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
printf '%s\n' "$x $y"
}
``` ```
## Get the architecture of the Operating System **Example Usage:**
```shell ```shell
"$HOSTTYPE" # Output: X Y
``` $ get_cursor_pos
1 8
## 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
"$SECONDS"
```
## Get a pseudorandom integer
Each time `$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*).
```shell
"$RANDOM"
``` ```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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@@ -1,78 +1,150 @@
# Information about the terminal # Conversion
## Get the terminal size in lines and columns (*from a script*) ## Convert a hex color to RGB
This is handy when writing scripts in pure bash and `stty`/`tput` can’t be
called.
**Example Function:** **Example Function:**
```sh ```sh
get_term_size() { hex_to_rgb() {
# Usage: get_term_size # Usage: hex_to_rgb "#FFFFFF"
((r=16#${1:1:2}))
((g=16#${1:3:2}))
((b=16#${1:5:6}))
# (:;:) is a micro sleep to ensure the variables are printf '%s\n' "$r $g $b"
# exported immediately.
shopt -s checkwinsize; (:;:)
printf '%s\n' "$LINES $COLUMNS"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
# Output: LINES COLUMNS $ hex_to_rgb "#FFFFFF"
$ get_term_size 255 255 255
15 55
``` ```
## Get the terminal size in pixels
**CAVEAT**: This does not work in some terminal emulators. ## Convert an RGB color to hex
**Example Function:** **Example Function:**
```sh ```sh
get_window_size() { rgb_to_hex() {
# Usage: get_window_size # Usage: rgb_to_hex "r" "g" "b"
printf '%b' "${TMUX:+\\ePtmux;\\e}\\e[14t${TMUX:+\\e\\\\}" printf '#%02x%02x%02x\n' "$1" "$2" "$3"
IFS=';t' read -d t -t 0.05 -sra term_size
printf '%s\n' "${term_size[1]}x${term_size[2]}"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
# Output: WIDTHxHEIGHT $ rgb_to_hex "255" "255" "255"
$ get_window_size #FFFFFF
1200x800
# Output (fail):
$ get_window_size
x
``` ```
## Get the current cursor position
This is useful when creating a TUI in pure bash. # Code Golf
**Example Function:** ## Shorter `for` loop syntax
```sh ```shell
get_cursor_pos() { # Tiny C Style.
# Usage: get_cursor_pos for((;i++<10;)){ echo "$i";}
IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
printf '%s\n' "$x $y" # Undocumented method.
for i in {1..10};{ echo "$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)
[[ "$var" == hello ]] && {
echo hi
# ...
} }
``` ```
**Example Usage:** ## Simpler `case` statement to set variable
We can use the `:` builtin to avoid repeating `variable=` in a case
statement. The `$_` variable stores the last argument of the last
successful command. `:` always succeeds so we can abuse it to store the
variable value.
```shell ```shell
# Output: X Y # Modified snippet from Neofetch.
$ get_cursor_pos case "$OSTYPE" in
1 8 "darwin"*)
: "MacOS"
;;
"linux"*)
: "Linux"
;;
*"bsd"* | "dragonfly" | "bitrig")
: "BSD"
;;
"cygwin" | "msys" | "win32")
: "Windows"
;;
*)
printf '%s\n' "Unknown OS detected, aborting..." >&2
exit 1
;;
esac
# Finally, set the variable.
os="$_"
``` ```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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@@ -1,150 +1,192 @@
# Conversion # Other
## Convert a hex color to RGB ## 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.
**CAVEAT:** Requires `bash` 4+
**Example Function:** **Example Function:**
```sh ```sh
hex_to_rgb() { read_sleep() {
# Usage: hex_to_rgb "#FFFFFF" # Usage: sleep 1
((r=16#${1:1:2})) # sleep 0.2
((g=16#${1:3:2})) read -rst "${1:-1}" -N 999
((b=16#${1:5:6}))
printf '%s\n' "$r $g $b"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
$ hex_to_rgb "#FFFFFF" read_sleep 1
255 255 255 read_sleep 0.1
read_sleep 30
``` ```
## Check if a program is in the user's PATH
## Convert an RGB color to hex ```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:** **Example Function:**
```sh ```sh
rgb_to_hex() { date() {
# Usage: rgb_to_hex "r" "g" "b" # Usage: date "format"
printf '#%02x%02x%02x\n' "$1" "$2" "$3" # See: 'man strftime' for format.
printf "%($1)T\\n" "-1"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
$ rgb_to_hex "255" "255" "255" # Using above function.
#FFFFFF $ 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' "$date"
Fri 15 Jun - 10:00 AM
``` ```
## Generate a UUID V4
# Code Golf **Example Function:**
## Shorter `for` loop syntax ```sh
uuid() {
# Usage: uuid
C="89ab"
```shell for ((N=0;N<16;++N)); do
# Tiny C Style. B="$((RANDOM%256))"
for((;i++<10;)){ echo "$i";}
# Undocumented method. case "$N" in
for i in {1..10};{ echo "$i";} 6) printf '4%x' "$((B%16))" ;;
8) printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
# Expansion. 3|5|7|9)
for i in {1..10}; do echo "$i"; done printf '%02x-' "$B"
# 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 "$OSTYPE" in
"darwin"*)
: "MacOS"
;;
"linux"*)
: "Linux"
;;
*"bsd"* | "dragonfly" | "bitrig")
: "BSD"
;;
"cygwin" | "msys" | "win32")
: "Windows"
;; ;;
*) *)
printf '%s\n' "Unknown OS detected, aborting..." >&2 printf '%02x' "$B"
exit 1
;; ;;
esac esac
done
# Finally, set the variable. printf '\n'
os="$_" }
```
**Example Usage:**
```shell
$ 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:**
```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
``` ```
<!-- CHAPTER END --> <!-- CHAPTER END -->

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@@ -1,193 +0,0 @@
# 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.
**CAVEAT:** Requires `bash` 4+
**Example Function:**
```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' "$date"
Fri 15 Jun - 10:00 AM
```
## Generate a UUID V4
**Example Function:**
```sh
uuid() {
# Usage: uuid
C="89ab"
for ((N=0;N<16;++N)); do
B="$((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:**
```shell
$ 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:**
```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
```
<!-- CHAPTER END -->

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@@ -1,9 +0,0 @@
# 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!
<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=V7QNJNKS3WYVS"><img src="https://img.shields.io/badge/donate-paypal-yellow.svg"></a> <a href="https://www.patreon.com/dyla"><img src="https://img.shields.io/badge/donate-patreon-yellow.svg"> </a><a href="https://liberapay.com/2211/"><img src="https://img.shields.io/badge/donate-liberapay-yellow.svg"></a>
Rock on. 🤘

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# Arrays # Loops
## Reverse an array ## Loop over a range of numbers
Enabling `extdebug` allows access to the `BASH_ARGV` array which stores Don't use `seq`.
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 ```shell
$ reverse_array 1 2 3 4 5 # Loop from 0-100 (no variable support).
5 for i in {0..100}; do
4 printf '%s\n' "$i"
3 done
2
1
$ arr=(red blue green)
$ reverse_array "${arr[@]}"
green
blue
red
``` ```
## Remove duplicate array elements ## Loop over a variable range of numbers
Create a temporary associative array. When setting associative array Don't use `seq`.
values and a duplicate assignment occurs, bash overwrites the key. This
allows us to effectively remove array duplicates.
**CAVEAT:** Requires `bash` 4+ ```shell
# Loop from 0-VAR.
VAR=50
for ((i=0;i<=VAR;i++)); do
printf '%s\n' "$i"
done
```
**Example Function:** ## Loop over an array
```sh ```shell
remove_array_dups() { arr=(apples oranges tomatoes)
# Usage: remove_array_dups "array"
declare -A tmp_array
for i in "$@"; do # Just elements.
[[ "$i" ]] && IFS=" " tmp_array["${i:- }"]=1 for element in "${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 done
printf '%s\n' "${!tmp_array[@]}" # Alternative method.
} for ((i=0;i<${#arr[@]};i++)); do
printf '%s\n' "${arr[$i]}"
done
``` ```
**Example Usage:** ## Loop over the contents of a file
```shell ```shell
$ remove_array_dups 1 1 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5 while read -r line; do
1 printf '%s\n' "$line"
2 done < "file"
3
4
5
$ arr=(red red green blue blue)
$ remove_array_dups "${arr[@]}"
red
green
blue
``` ```
## Random array element ## Loop over files and directories
**Example Function:** Don’t use `ls`.
```sh
random_array_element() {
# Usage: random_array_element "array"
local arr=("$@")
printf '%s\n' "${arr[RANDOM % $#]}"
}
```
**Example Usage:**
```shell ```shell
$ array=(red green blue yellow brown) # Greedy example.
$ random_array_element "${array[@]}" for file in *; do
yellow printf '%s\n' "$file"
done
# You can also just pass multiple arguments. # PNG files in dir.
$ random_array_element 1 2 3 4 5 6 7 for file in ~/Pictures/*.png; do
3 printf '%s\n' "$file"
``` done
## Cycle through an array # Iterate over directories.
for dir in ~/Downloads/*/; do
printf '%s\n' "$dir"
done
Each time the `printf` is called, the next array element is printed. When # Brace Expansion.
the print hits the last array element it starts from the first element for file in /path/to/parentdir/{file1,file2,subdir/file3}; do
again. printf '%s\n' "$file"
done
```sh # Iterate recursively.
arr=(a b c d) shopt -s globstar
for file in ~/Pictures/**/*; do
cycle() { printf '%s\n' "$file"
printf '%s ' "${arr[${i:=0}]}" done
((i=i>=${#arr[@]}-1?0:++i)) shopt -u globstar
}
```
## Toggle between two values
This works the same as above, this is just a different use case.
```sh
arr=(true false)
cycle() {
printf '%s ' "${arr[${i:=0}]}"
((i=i>=${#arr[@]}-1?0:++i))
}
``` ```
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# Loops # File handling
## Loop over a range of numbers **CAVEAT:** `bash` doesn't handle binary data properly in versions `< 4.4`.
Don't use `seq`. ## Read a file to a string
Alternative to the `cat` command.
```shell ```shell
# Loop from 0-100 (no variable support). file_data="$(<"file")"
for i in {0..100}; do
printf '%s\n' "$i"
done
``` ```
## Loop over a variable range of numbers ## Read a file to an array (*by line*)
Don't use `seq`. Alternative to the `cat` command.
```shell ```shell
# Loop from 0-VAR. # Bash <4
VAR=50 IFS=$'\n' read -d "" -ra file_data < "file"
for ((i=0;i<=VAR;i++)); do
printf '%s\n' "$i" # Bash 4+
done mapfile -t file_data < "file"
``` ```
## Loop over an array ## Get the first N lines of a file
```shell Alternative to the `head` command.
arr=(apples oranges tomatoes)
# Just elements. **CAVEAT:** Requires `bash` 4+
for element in "${arr[@]}"; do
printf '%s\n' "$element" **Example Function:**
done
```sh
head() {
# Usage: head "n" "file"
mapfile -tn "$1" line < "$2"
printf '%s\n' "${line[@]}"
}
``` ```
## Loop over an array with an index **Example Usage:**
```shell ```shell
arr=(apples oranges tomatoes) $ head 2 ~/.bashrc
# Prompt
PS1='➜ '
# Elements and index. $ head 1 ~/.bashrc
for i in "${!arr[@]}"; do # Prompt
printf '%s\n' "${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 ## 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 ```shell
while read -r line; do $ 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" printf '%s\n' "$line"
done < "file"
[[ "$line" == "$2" ]] && extract=1
[[ "$line" == "$3" ]] && extract=
done < "$1"
}
``` ```
## Loop over files and directories **Example Usage:**
Don’t use `ls`.
```shell ```shell
# Greedy example. # Extract code blocks from MarkDown file.
for file in *; do $ extract ~/projects/pure-bash/README.md '```sh' '```'
printf '%s\n' "$file" # Output here...
done
# PNG files in dir.
for file in ~/Pictures/*.png; do
printf '%s\n' "$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' "$file"
done
shopt -u globstar
``` ```
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# File handling # File Paths
**CAVEAT:** `bash` doesn't handle binary data properly in versions `< 4.4`. ## Get the directory name of a file path
## Read a file to a string Alternative to the `dirname` command.
Alternative to the `cat` command.
```shell
file_data="$(<"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:** **Example Function:**
```sh ```sh
head() { dirname() {
# Usage: head "n" "file" # Usage: dirname "path"
mapfile -tn "$1" line < "$2" printf '%s\n' "${1%/*}/"
printf '%s\n' "${line[@]}"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
$ head 2 ~/.bashrc $ dirname ~/Pictures/Wallpapers/1.jpg
# Prompt /home/black/Pictures/Wallpapers/
PS1='➜ '
$ head 1 ~/.bashrc $ dirname ~/Pictures/Downloads/
# Prompt /home/black/Pictures/
``` ```
## Get the last N lines of a file ## Get the base-name of a file path
Alternative to the `tail` command. Alternative to the `basename` command.
**CAVEAT:** Requires `bash` 4+
**Example Function:** **Example Function:**
```sh ```sh
tail() { basename() {
# Usage: tail "n" "file" # Usage: basename "path"
mapfile -tn 0 line < "$2" : "${1%/}"
printf '%s\n' "${line[@]: -$1}" printf '%s\n' "${_##*/}"
} }
``` ```
**Example Usage:** **Example Usage:**
```shell ```shell
$ tail 2 ~/.bashrc $ basename ~/Pictures/Wallpapers/1.jpg
# Enable tmux. 1.jpg
# [[ -z "$TMUX" ]] && exec tmux
$ tail 1 ~/.bashrc $ basename ~/Pictures/Downloads/
# [[ -z "$TMUX" ]] && exec tmux Downloads
```
## 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...
``` ```
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# File Paths # Variables
## Get the directory name of a file path ## Assign and access a variable using a variable
Alternative to the `dirname` command.
**Example Function:**
```sh
dirname() {
# Usage: dirname "path"
printf '%s\n' "${1%/*}/"
}
```
**Example Usage:**
```shell ```shell
$ dirname ~/Pictures/Wallpapers/1.jpg hello_world="test"
/home/black/Pictures/Wallpapers/
$ dirname ~/Pictures/Downloads/ # Create the variable name.
/home/black/Pictures/ var1="world"
``` var2="hello_${var1}"
## Get the base-name of a file path # Print the value of the variable name stored in 'hello_$var1'.
printf '%s\n' "${!var2}"
Alternative to the `basename` command.
**Example Function:**
```sh
basename() {
# Usage: basename "path"
: "${1%/}"
printf '%s\n' "${_##*/}"
}
```
**Example Usage:**
```shell
$ basename ~/Pictures/Wallpapers/1.jpg
1.jpg
$ basename ~/Pictures/Downloads/
Downloads
``` ```
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# Variables # Escape Sequences
## Assign and access a variable using a variable 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.
```shell ## Text Colors
hello_world="test"
# Create the variable name. **NOTE:** Sequences requiring RGB values only work in True-Color Terminal Emulators.
var1="world"
var2="hello_${var1}" | Sequence | What does it do? | Value |
| -------- | ---------------- | ----- |
| `\e[38;5;<NUM>m` | Set text foreground color. | `0-255`
| `\e[48;5;<NUM>m` | Set text background color. | `0-255`
| `\e[38;2;<R>;<G>;<B>m` | Set text foreground color to RGB color. | `R`, `G`, `B`
| `\e[48;2;<R>;<G>;<B>m` | Set text background color to RGB color. | `R`, `G`, `B`
## Text Attributes
| Sequence | What does it do? |
| -------- | ---------------- |
| `\e[m` | Reset text formatting and colors.
| `\e[1m` | Bold text. |
| `\e[2m` | Faint text. |
| `\e[3m` | Italic text. |
| `\e[4m` | Underline text. |
| `\e[5m` | Slow blink. |
| `\e[7m` | Swap foreground and background colors. |
## Cursor Movement
| Sequence | What does it do? | Value |
| -------- | ---------------- | ----- |
| `\e[<LINE>;<COLUMN>H` | Move cursor to absolute position. | `line`, `column`
| `\e[H` | Move cursor to home position (`0,0`). |
| `\e[<NUM>A` | Move cursor up N lines. | `num`
| `\e[<NUM>B` | Move cursor down N lines. | `num`
| `\e[<NUM>C` | Move cursor right N columns. | `num`
| `\e[<NUM>D` | Move cursor left N columns. | `num`
| `\e[s` | Save cursor position. |
| `\e[u` | Restore cursor position. |
## Erasing Text
| Sequence | What does it do? |
| -------- | ---------------- |
| `\e[K` | Erase from cursor position to end of line.
| `\e[1K` | Erase from cursor position to start of line.
| `\e[2K` | Erase the entire current line.
| `\e[J` | Erase from the current line to the bottom of the screen.
| `\e[1J` | Erase from the current line to the top of the screen.
| `\e[2J` | Clear the screen.
| `\e[2J\e[H` | Clear the screen and move cursor to `0,0`.
# Print the value of the variable name stored in 'hello_$var1'.
printf '%s\n' "${!var2}"
```
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# Escape Sequences # Parameter Expansion
Contrary to popular belief, there's no issue in using raw escape sequences. Using `tput` just abstracts the same ANSI escape sequences. What's worse is that `tput` isn't actually portable, there are a number of different `tput` variants on different Operating Systems each with different commands (*try and run `tput setaf 3` on a FreeBSD system*). The easiest solution ends up being raw ANSI sequences. ## Indirection
## Text Colors | Parameter | What does it do? |
| --------- | ---------------- |
**NOTE:** Sequences requiring RGB values only work in True-Color Terminal Emulators. | `${!VAR}` | Access a variable based on the value of `VAR`. See: [link](#assign-and-access-a-variable-using-a-variable)
| `${!VAR*}` | Expand to `IFS` separated list of variable names starting with `VAR`. |
| Sequence | What does it do? | Value | | `${!VAR@}` | Expand to `IFS` separated list of variable names starting with `VAR`. |
| -------- | ---------------- | ----- |
| `\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 ## Replacement
| Sequence | What does it do? | Value | | Parameter | What does it do? |
| -------- | ---------------- | ----- | | --------- | ---------------- |
| `\e[<LINE>;<COLUMN>H` | Move cursor to absolute position. | `line`, `column` | `${VAR#PATTERN}` | Remove shortest match of pattern from start of string. |
| `\e[H` | Move cursor to home position (`0,0`). | | `${VAR##PATTERN}` | Remove longest match of pattern from start of string. |
| `\e[<NUM>A` | Move cursor up N lines. | `num` | `${VAR%PATTERN}` | Remove shortest match of pattern from end of string. |
| `\e[<NUM>B` | Move cursor down N lines. | `num` | `${VAR%%PATTERN}` | Remove longest match of pattern from end of string. |
| `\e[<NUM>C` | Move cursor right N columns. | `num` | `${VAR/PATTERN/REPLACE}` | Replace first match with string.
| `\e[<NUM>D` | Move cursor left N columns. | `num` | `${VAR//PATTERN/REPLACE}` | Replace all matches with string.
| `\e[s` | Save cursor position. | | `${VAR/PATTERN}` | Remove first match.
| `\e[u` | Restore cursor position. | | `${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. <br> (`${VAR:10:10}`: Get sub-string from char `10` to char `20`)
| `${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+` |
| `${VAR,,}` | Lowercase all characters. | `bash 4+` |
## Erasing Text ## Default Value
| Sequence | What does it do? | | Parameter | What does it do? |
| -------- | ---------------- | | --------- | ---------------- |
| `\e[K` | Erase from cursor position to end of line. | `${VAR:-STRING}` | If `VAR` is empty or unset, use `STRING` as it's value.
| `\e[1K` | Erase from cursor position to start of line. | `${VAR-STRING}` | If `VAR` is unset, use `STRING` as it's value.
| `\e[2K` | Erase the entire current line. | `${VAR:=STRING}` | If `VAR` is empty or unset, set the value of `VAR` to `STRING`.
| `\e[J` | Erase from the current line to the bottom of the screen. | `${VAR=STRING}` | If `VAR` is unset, set the value of `VAR` to `STRING`.
| `\e[1J` | Erase from the current line to the top of the screen. | `${VAR:+STRING}` | If `VAR` isn't empty, use `STRING` as it's value.
| `\e[2J` | Clear the screen. | `${VAR+STRING}` | If `VAR` is set, use `STRING` as it's value.
| `\e[2J\e[H` | Clear the screen and move cursor to `0,0`. | `${VAR:?STRING}` | Display an error if empty or unset.
| `${VAR?STRING}` | Display an error if unset.
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# Parameter Expansion # Brace Expansion
## Indirection ## Ranges
| Parameter | What does it do? | ```shell
| --------- | ---------------- | # Syntax: {<START>..<END>}
| `${!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`. |
# Print numbers 1-100.
echo {1..100}
## Replacement # Print range of floats.
echo 1.{1..9}
| Parameter | What does it do? | # Print chars a-z.
| --------- | ---------------- | echo {a..z}
| `${VAR#PATTERN}` | Remove shortest match of pattern from start of string. | echo {A..Z}
| `${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 # Nesting.
echo {A..Z}{0..9}
| Parameter | What does it do? | # Print zero-padded numbers.
| --------- | ---------------- | # CAVEAT: bash 4+
| `${#VAR}` | Length of var in characters. echo {01..100}
| `${#ARR[@]}` | Length of array in elements.
## Expansion # Change increment amount.
# Syntax: {<START>..<END>..<INCREMENT>}
# CAVEAT: bash 4+
echo {1..10..2} # Increment by 2.
```
| Parameter | What does it do? | ## String Lists
| --------- | ---------------- |
| `${VAR:OFFSET}` | Remove first `N` chars from variable.
| `${VAR:OFFSET:LENGTH}` | Get substring from `N` character to `N` character. <br> (`${VAR:10:10}`: Get sub-string from char `10` to char `20`)
| `${VAR:: OFFSET}` | Get first `N` chars from variable.
| `${VAR:: -OFFSET}` | Remove last `N` chars from variable.
| `${VAR: -OFFSET}` | Get last `N` chars from variable.
| `${VAR:OFFSET:-OFFSET}` | Cut first `N` chars and last `N` chars. | `bash 4.2+` |
## Case Modification ```shell
echo {apples,oranges,pears,grapes}
| Parameter | What does it do? | CAVEAT |
| --------- | ---------------- | ------ |
| `${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.
# Example Usage:
# Remove dirs Movies, Music and ISOS from ~/Downloads/.
rm -rf ~/Downloads/{Movies,Music,ISOS}
```
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# Brace Expansion # Arithmetic
## Ranges ## Simpler syntax to set variables
```shell ```shell
# Syntax: {<START>..<END>} # Simple math
((var=1+2))
# Print numbers 1-100. # Decrement/Increment variable
echo {1..100} ((var++))
((var--))
((var+=1))
((var-=1))
# Print range of floats. # Using variables
echo 1.{1..9} ((var=var2*arr[2]))
# 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 ## Ternary tests
```shell ```shell
echo {apples,oranges,pears,grapes} # Set the value of var to var2 if var2 is greater than var.
# var: variable to set.
# Example Usage: # var2>var: Condition to test.
# Remove dirs Movies, Music and ISOS from ~/Downloads/. # ?var2: If the test succeeds.
rm -rf ~/Downloads/{Movies,Music,ISOS} # :var: If the test fails.
((var=var2>var?var2:var))
``` ```
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