diff --git a/manuscript/Book.txt b/manuscript/Book.txt
index b4a1249..b56dfe1 100644
--- a/manuscript/Book.txt
+++ b/manuscript/Book.txt
@@ -17,3 +17,4 @@ chapter15.txt
 chapter16.txt
 chapter17.txt
 chapter18.txt
+chapter19.txt
diff --git a/manuscript/chapter10.txt b/manuscript/chapter10.txt
index 36c5887..d7d7ac4 100644
--- a/manuscript/chapter10.txt
+++ b/manuscript/chapter10.txt
@@ -1,58 +1,59 @@
 
-# ARITHMETIC OPERATORS
+# CONDITIONAL EXPRESSIONS
 
-## Assignment
+## File Conditionals
 
-| Operators | What does it do? |
-| --------- | ---------------- |
-| `=` | Initialize or change the value of a variable.
+| Expression | Value  | What does it do? |
+| ---------- | ------ | ---------------- |
+| `-a`       | `file` | If file exists.
+| `-b`       | `file` | If file exists and is a block special file.
+| `-c`       | `file` | If file exists and is a character special file.
+| `-d`       | `file` | If file exists and is a directory.
+| `-e`       | `file` | If file exists.
+| `-f`       | `file` | If file exists and is a regular file.
+| `-g`       | `file` | If file exists and its set-group-id bit is set.
+| `-h`       | `file` | If file exists and is a symbolic link.
+| `-k`       | `file` | If file exists and its sticky-bit is set
+| `-p`       | `file` | If file exists and is a named pipe (*FIFO*).
+| `-r`       | `file` | If file exists and is readable.
+| `-s`       | `file` | If file exists and its size is greater than zero.
+| `-t`       | `fd`   | If file descriptor is open and refers to a terminal.
+| `-u`       | `file` | If file exists and its set-user-id bit is set.
+| `-w`       | `file` | If file exists and is writable.
+| `-x`       | `file` | If file exists and is executable.
+| `-G`       | `file` | If file exists and is owned by the effective group ID.
+| `-L`       | `file` | If file exists and is a symbolic link.
+| `-N`       | `file` | If file exists and has been modified since last read.
+| `-O`       | `file` | If file exists and is owned by the effective user ID.
+| `-S`       | `file` | If file exists and is a socket.
 
-## Arithmetic
+## File Comparisons
 
-| Operators | What does it do? |
-| --------- | ---------------- |
-| `+` | Addition
-| `-` | Subtraction
-| `*` | Multiplication
-| `/` | Division
-| `**` | Exponentiation
-| `%` | Modulo
-| `+=` | Plus-Equal (*Increment a variable.*)
-| `-=` | Minus-Equal (*Decrement a variable.*)
-| `*=` | Times-Equal (*Multiply a variable.*)
-| `/=` | Slash-Equal (*Divide a variable.*)
-| `%=` | Mod-Equal (*Remainder of dividing a variable.*)
+| Expression | What does it do? |
+| ---------- | ---------------- |
+| `file -ef file2` | If both files refer to the same inode and device numbers.
+| `file -nt file2` | If `file` is newer than `file2` (*uses modification ime*) or `file` exists and `file2` does not.
+| `file -ot file2` | If `file` is older than `file2` (*uses modification ime*) or `file2` exists and `file` does not.
 
-## Bitwise
+## Variable Conditionals
 
-| Operators | What does it do? |
-| --------- | ---------------- |
-| `<<` | Bitwise Left Shift
-| `<<=` | Left-Shift-Equal
-| `>>` | Bitwise Right Shift
-| `>>=` | Right-Shift-Equal
-| `&` | Bitwise AND
-| `&=` | Bitwise AND-Equal
-| `\|` | Bitwise OR
-| `\|=` | Bitwise OR-Equal
-| `~` | Bitwise NOT
-| `^` | Bitwise XOR
-| `^=` | Bitwise XOR-Equal
+| Expression | Value | What does it do? |
+| ---------- | ----- | ---------------- |
+| `-o`       | `opt` | If shell option is enabled.
+| `-v`       | `var` | If variable has a value assigned.
+| `-R`       | `var` | If variable is a name reference.
+| `-z`       | `var` | If the length of string is zero.
+| `-n`       | `var` | If the length of string is non-zero.
 
-## Logical
-
-| Operators | What does it do? |
-| --------- | ---------------- |
-| `!` | NOT
-| `&&` | AND
-| `\|\|` | OR
-
-## Miscellaneous
-
-| Operators | What does it do? | Example |
-| --------- | ---------------- | ------- |
-| `,` | Comma Separator | `((a=1,b=2,c=3))`
+## Variable Comparisons
 
+| Expression | What does it do? |
+| ---------- | ---------------- |
+| `var = var2` | Equal to.
+| `var == var2` | Equal to (*synonym for `=`*).
+| `var != var2` | Not equal to.
+| `var < var2` | Less than (*in ASCII alphabetical order.*)
+| `var > var2` | Greater than (*in ASCII alphabetical order.*)
 
 <!-- CHAPTER END -->
 
diff --git a/manuscript/chapter11.txt b/manuscript/chapter11.txt
index e7e3f0b..fedbce7 100644
--- a/manuscript/chapter11.txt
+++ b/manuscript/chapter11.txt
@@ -1,31 +1,58 @@
-# ARITHMETIC
 
-## Simpler syntax to set variables
+# ARITHMETIC OPERATORS
 
-```shell
-# Simple math
-((var=1+2))
+## Assignment
 
-# Decrement/Increment variable
-((var++))
-((var--))
-((var+=1))
-((var-=1))
+| Operators | What does it do? |
+| --------- | ---------------- |
+| `=`       | Initialize or change the value of a variable.
 
-# Using variables
-((var=var2*arr[2]))
-```
+## Arithmetic
 
-## Ternary Tests
+| Operators | What does it do? |
+| --------- | ---------------- |
+| `+` | Addition
+| `-` | Subtraction
+| `*` | Multiplication
+| `/` | Division
+| `**` | Exponentiation
+| `%` | Modulo
+| `+=` | Plus-Equal (*Increment a variable.*)
+| `-=` | Minus-Equal (*Decrement a variable.*)
+| `*=` | Times-Equal (*Multiply a variable.*)
+| `/=` | Slash-Equal (*Divide a variable.*)
+| `%=` | Mod-Equal (*Remainder of dividing a variable.*)
+
+## Bitwise
+
+| Operators | What does it do? |
+| --------- | ---------------- |
+| `<<` | Bitwise Left Shift
+| `<<=` | Left-Shift-Equal
+| `>>` | Bitwise Right Shift
+| `>>=` | Right-Shift-Equal
+| `&` | Bitwise AND
+| `&=` | Bitwise AND-Equal
+| `\|` | Bitwise OR
+| `\|=` | Bitwise OR-Equal
+| `~` | Bitwise NOT
+| `^` | Bitwise XOR
+| `^=` | Bitwise XOR-Equal
+
+## Logical
+
+| Operators | What does it do? |
+| --------- | ---------------- |
+| `!` | NOT
+| `&&` | AND
+| `\|\|` | OR
+
+## Miscellaneous
+
+| Operators | What does it do? | Example |
+| --------- | ---------------- | ------- |
+| `,` | Comma Separator | `((a=1,b=2,c=3))`
 
-```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))
-```
 
 <!-- CHAPTER END -->
 
diff --git a/manuscript/chapter12.txt b/manuscript/chapter12.txt
index 14c380b..e7e3f0b 100644
--- a/manuscript/chapter12.txt
+++ b/manuscript/chapter12.txt
@@ -1,42 +1,30 @@
-# TRAPS
+# ARITHMETIC
 
-Traps allow a script to execute code on various signals. In [pxltrm](https://github.com/dylanaraps/pxltrm) (*a pixel art editor written in bash*)  traps are used to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit.
-
-Traps should be added near the start of scripts so any early errors are also caught.
-
-**NOTE:** For a full list of signals, see `trap -l`.
-
-
-## Do something on script exit
+## Simpler syntax to set variables
 
 ```shell
-# Clear screen on script exit.
-trap 'printf \\e[2J\\e[H\\e[m' EXIT
+# Simple math
+((var=1+2))
+
+# Decrement/Increment variable
+((var++))
+((var--))
+((var+=1))
+((var-=1))
+
+# Using variables
+((var=var2*arr[2]))
 ```
 
-## Ignore terminal interrupt (CTRL+C, SIGINT)
+## Ternary Tests
 
 ```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
+# 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))
 ```
 
 <!-- CHAPTER END -->
diff --git a/manuscript/chapter13.txt b/manuscript/chapter13.txt
index 3e49886..14c380b 100644
--- a/manuscript/chapter13.txt
+++ b/manuscript/chapter13.txt
@@ -1,13 +1,42 @@
-# PERFORMANCE
+# TRAPS
 
-## Disable Unicode
+Traps allow a script to execute code on various signals. In [pxltrm](https://github.com/dylanaraps/pxltrm) (*a pixel art editor written in bash*)  traps are used to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit.
 
-If unicode is not required, it can be disabled for a performance increase. Results may vary however there have been noticeable improvements in [neofetch](https://github.com/dylanaraps/neofetch) and other programs.
+Traps should be added near the start of scripts so any early errors are also caught.
+
+**NOTE:** For a full list of signals, see `trap -l`.
+
+
+## Do something on script exit
 
 ```shell
-# Disable unicode.
-LC_ALL=C
-LANG=C
+# Clear screen on script exit.
+trap 'printf \\e[2J\\e[H\\e[m' EXIT
+```
+
+## 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 -->
diff --git a/manuscript/chapter14.txt b/manuscript/chapter14.txt
index e03af79..3e49886 100644
--- a/manuscript/chapter14.txt
+++ b/manuscript/chapter14.txt
@@ -1,51 +1,13 @@
-# OBSOLETE SYNTAX
+# PERFORMANCE
 
-## Shebang
+## Disable Unicode
 
-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.
+If unicode is not required, it can be disabled for a performance increase. Results may vary however there have been noticeable improvements in [neofetch](https://github.com/dylanaraps/neofetch) and other programs.
 
 ```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
-
-Do not use the `function` keyword, it reduces compatibility with older versions of `bash`.
-
-```shell
-# Right.
-do_something() {
-    # ...
-}
-
-# Wrong.
-function do_something() {
-    # ...
-}
+# Disable unicode.
+LC_ALL=C
+LANG=C
 ```
 
 <!-- CHAPTER END -->
diff --git a/manuscript/chapter15.txt b/manuscript/chapter15.txt
index 2aaaa32..e03af79 100644
--- a/manuscript/chapter15.txt
+++ b/manuscript/chapter15.txt
@@ -1,93 +1,51 @@
-# INTERNAL VARIABLES
+# OBSOLETE SYNTAX
 
-## Get the location to the `bash` binary
+## 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
-"$BASH"
+# Right:
+
+    #!/usr/bin/env bash
+
+# Wrong:
+
+    #!/bin/bash
 ```
 
-## Get the version of the current running `bash` process
+## Command Substitution
+
+Use `$()` instead of `` ` ` ``.
 
 ```shell
-# As a string.
-"$BASH_VERSION"
+# Right.
+var="$(command)"
 
-# As an array.
-"${BASH_VERSINFO[@]}"
+# Wrong.
+var=`command`
+
+# $() can easily be nested whereas `` cannot.
+var="$(command "$(command)")"
 ```
 
-## Open the user's preferred text editor
+## Function Declaration
+
+Do not use the `function` keyword, it reduces compatibility with older versions of `bash`.
 
 ```shell
-"$EDITOR" "$file"
+# Right.
+do_something() {
+    # ...
+}
 
-# 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"
-```
-
-## 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"
+# Wrong.
+function do_something() {
+    # ...
+}
 ```
 
 <!-- CHAPTER END -->
diff --git a/manuscript/chapter16.txt b/manuscript/chapter16.txt
index 9ebc228..2aaaa32 100644
--- a/manuscript/chapter16.txt
+++ b/manuscript/chapter16.txt
@@ -1,78 +1,93 @@
-# INFORMATION ABOUT THE TERMINAL
+# INTERNAL VARIABLES
 
-## 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:**
+## Get the location to the `bash` binary
 
 ```shell
-# Output: LINES COLUMNS
-$ get_term_size
-15 55
+"$BASH"
 ```
 
-## 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:**
+## Get the version of the current running `bash` process
 
 ```shell
-# Output: WIDTHxHEIGHT
-$ get_window_size
-1200x800
+# As a string.
+"$BASH_VERSION"
 
-# Output (fail):
-$ get_window_size
-x
+# As an array.
+"${BASH_VERSINFO[@]}"
 ```
 
-## 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:**
+## Open the user's preferred text editor
 
 ```shell
-# Output: X Y
-$ get_cursor_pos
-1 8
+"$EDITOR" "$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"
+```
+
+## 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 -->
diff --git a/manuscript/chapter17.txt b/manuscript/chapter17.txt
index 0da32b3..9ebc228 100644
--- a/manuscript/chapter17.txt
+++ b/manuscript/chapter17.txt
@@ -1,145 +1,78 @@
-# CONVERSION
+# INFORMATION ABOUT THE TERMINAL
 
-## Convert a hex color to RGB
+## 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
-hex_to_rgb() {
-    # Usage: hex_to_rgb "#FFFFFF"
-    : "${1/\#}"
-    ((r=16#${_:0:2},g=16#${_:2:2},b=16#${_:4:2}))
-    printf '%s\n' "$r $g $b"
+get_term_size() {
+    # Usage: get_term_size
+
+    # (:;:) is a micro sleep to ensure the variables are
+    # exported immediately.
+    shopt -s checkwinsize; (:;:)
+    printf '%s\n' "$LINES $COLUMNS"
 }
 ```
 
 **Example Usage:**
 
 ```shell
-$ hex_to_rgb "#FFFFFF"
-255 255 255
+# Output: LINES COLUMNS
+$ get_term_size
+15 55
 ```
 
+## Get the terminal size in pixels
 
-## Convert an RGB color to hex
+**CAVEAT**: This does not work in some terminal emulators.
 
 **Example Function:**
 
 ```sh
-rgb_to_hex() {
-    # Usage: rgb_to_hex "r" "g" "b"
-    printf '#%02x%02x%02x\n' "$1" "$2" "$3"
+get_window_size() {
+    # Usage: get_window_size
+    printf '%b' "${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
-$ rgb_to_hex "255" "255" "255"
-#FFFFFF
+# Output: WIDTHxHEIGHT
+$ get_window_size
+1200x800
+
+# Output (fail):
+$ get_window_size
+x
 ```
 
+## Get the current cursor position
 
-# CODE GOLF
+This is useful when creating a TUI in pure bash.
 
-## Shorter `for` loop syntax
+**Example Function:**
 
-```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
-# This can be used to assign integer values.
-# Example: f a=1
-#          f a++
-f()(($1))
-
-# Using tests, loops etc.
-# NOTE: ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’ can also be used.
-f()if true; then echo "$1"; fi
-f()for i in "$@"; do echo "$i"; done
-```
-
-## Shorter `if` syntax
-
-```shell
-# One line
-# Note: The 3rd statement may run when the 1st is true
-[[ "$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
-    # ...
+```sh
+get_cursor_pos() {
+    # Usage: get_cursor_pos
+    IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
+    printf '%s\n' "$x $y"
 }
 ```
 
-## Simpler `case` statement to set variable
-
-The `:` built-in can be used to avoid repeating `variable=` in a case statement. The `$_` variable stores the last argument of the last command. `:` always succeeds so it can be used to store the variable value.
+**Example Usage:**
 
 ```shell
-# Modified snippet from Neofetch.
-case "$OSTYPE" in
-    "darwin"*)
-        : "MacOS"
-    ;;
-
-    "linux"*)
-        : "Linux"
-    ;;
-
-    *"bsd"* | "dragonfly" | "bitrig")
-        : "BSD"
-    ;;
-
-    "cygwin" | "msys" | "win32")
-        : "Windows"
-    ;;
-
-    *)
-        printf '%s\n' "Unknown OS detected, aborting..." >&2
-        exit 1
-    ;;
-esac
-
-# Finally, set the variable.
-os="$_"
+# Output: X Y
+$ get_cursor_pos
+1 8
 ```
 
 <!-- CHAPTER END -->
diff --git a/manuscript/chapter18.txt b/manuscript/chapter18.txt
index f575993..a683fae 100644
--- a/manuscript/chapter18.txt
+++ b/manuscript/chapter18.txt
@@ -1,189 +1,146 @@
-# OTHER
+# CONVERSION
 
-## Use `read` as an alternative to the `sleep` command
-
-Surprisingly, `sleep` is an external command and not a `bash` built-in.
-
-**CAVEAT:** Requires `bash` 4+
+## Convert a hex color to RGB
 
 **Example Function:**
 
 ```sh
-read_sleep() {
-    # Usage: sleep 1
-    #        sleep 0.2
-    read -rst "${1:-1}" -N 999
+hex_to_rgb() {
+    # Usage: hex_to_rgb "#FFFFFF"
+    #        hex_to_rgb "000000"
+    : "${1/\#}"
+    ((r=16#${_:0:2},g=16#${_:2:2},b=16#${_:4:2}))
+    printf '%s\n' "$r $g $b"
 }
 ```
 
 **Example Usage:**
 
 ```shell
-read_sleep 1
-read_sleep 0.1
-read_sleep 30
+$ hex_to_rgb "#FFFFFF"
+255 255 255
 ```
 
-## Check if a program is in the user's PATH
 
-```shell
-# There are 3 ways to do this and either one can be used.
-type -p executable_name &>/dev/null
-hash executable_name &>/dev/null
-command -v executable_name &>/dev/null
-
-# As a test.
-if type -p executable_name &>/dev/null; then
-    # Program is in PATH.
-fi
-
-# Inverse.
-if ! type -p executable_name &>/dev/null; then
-    # Program is not in PATH.
-fi
-
-# Example (Exit early if program is not installed).
-if ! type -p convert &>/dev/null; then
-    printf '%s\n' "error: convert is not installed, exiting..."
-    exit 1
-fi
-```
-
-## Get the current date using `strftime`
-
-Bash’s `printf` has a built-in method of getting the date which can be used in place of the `date` command.
-
-**CAVEAT:** Requires `bash` 4+
+## Convert an RGB color to hex
 
 **Example Function:**
 
 ```sh
-date() {
-    # Usage: date "format"
-    # See: 'man strftime' for format.
-    printf "%($1)T\\n" "-1"
+rgb_to_hex() {
+    # Usage: rgb_to_hex "r" "g" "b"
+    printf '#%02x%02x%02x\n' "$1" "$2" "$3"
 }
 ```
 
 **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' "$date"
-Fri 15 Jun  - 10:00 AM
+$ rgb_to_hex "255" "255" "255"
+#FFFFFF
 ```
 
-## Generate a UUID V4
 
-**Example Function:**
+# CODE GOLF
 
-```sh
-uuid() {
-    # Usage: uuid
-    C="89ab"
+## Shorter `for` loop syntax
 
-    for ((N=0;N<16;++N)); do
-        B="$((RANDOM%256))"
+```shell
+# Tiny C Style.
+for((;i++<10;)){ echo "$i";}
 
-        case "$N" in
-            6)  printf '4%x' "$((B%16))" ;;
-            8)  printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
+# Undocumented method.
+for i in {1..10};{ echo "$i";}
 
-            3|5|7|9)
-                printf '%02x-' "$B"
-            ;;
+# Expansion.
+for i in {1..10}; do echo "$i"; done
 
-            *)
-                printf '%02x' "$B"
-            ;;
-        esac
-    done
+# C Style.
+for((i=0;i<=10;i++)); do echo "$i"; done
+```
 
-    printf '\n'
+## 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
+# This can be used to assign integer values.
+# Example: f a=1
+#          f a++
+f()(($1))
+
+# Using tests, loops etc.
+# NOTE: ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’ can also be used.
+f()if true; then echo "$1"; fi
+f()for i in "$@"; do echo "$i"; done
+```
+
+## Shorter `if` syntax
+
+```shell
+# One line
+# Note: The 3rd statement may run when the 1st is true
+[[ "$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
+
+The `:` built-in can be used to avoid repeating `variable=` in a case statement. The `$_` variable stores the last argument of the last command. `:` always succeeds so it can be used to store the variable value.
 
 ```shell
-$ uuid
-d5b6c731-1310-4c24-9fe3-55d556d44374
-```
+# Modified snippet from Neofetch.
+case "$OSTYPE" in
+    "darwin"*)
+        : "MacOS"
+    ;;
 
-## Progress bars
+    "linux"*)
+        : "Linux"
+    ;;
 
-This is a simple way of drawing progress bars without needing a for loop
-in the function itself.
+    *"bsd"* | "dragonfly" | "bitrig")
+        : "BSD"
+    ;;
 
-**Example Function:**
+    "cygwin" | "msys" | "win32")
+        : "Windows"
+    ;;
 
-```sh
-bar() {
-    # Usage: bar 1 10
-    #            ^----- Elapsed Percentage (0-100).
-    #               ^-- Total length in chars.
-    ((elapsed=$1*$2/100))
+    *)
+        printf '%s\n' "Unknown OS detected, aborting..." >&2
+        exit 1
+    ;;
+esac
 
-    # 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 in a 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
+# Finally, set the variable.
+os="$_"
 ```
 
 <!-- CHAPTER END -->
diff --git a/manuscript/chapter19.txt b/manuscript/chapter19.txt
new file mode 100644
index 0000000..f575993
--- /dev/null
+++ b/manuscript/chapter19.txt
@@ -0,0 +1,190 @@
+# OTHER
+
+## Use `read` as an alternative to the `sleep` command
+
+Surprisingly, `sleep` is an external command and not a `bash` built-in.
+
+**CAVEAT:** Requires `bash` 4+
+
+**Example Function:**
+
+```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 either one can be used.
+type -p executable_name &>/dev/null
+hash executable_name &>/dev/null
+command -v executable_name &>/dev/null
+
+# As a test.
+if type -p executable_name &>/dev/null; then
+    # Program is in PATH.
+fi
+
+# Inverse.
+if ! type -p executable_name &>/dev/null; then
+    # Program is not in PATH.
+fi
+
+# Example (Exit early if program is not installed).
+if ! type -p convert &>/dev/null; then
+    printf '%s\n' "error: convert is not installed, exiting..."
+    exit 1
+fi
+```
+
+## Get the current date using `strftime`
+
+Bash’s `printf` has a built-in method of getting the date which can be used in place of the `date` command.
+
+**CAVEAT:** Requires `bash` 4+
+
+**Example Function:**
+
+```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 in a 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 -->
+