Added build files to turn the bible into a book

manuscript/chapter15.txt

@@ -1,78 +1,150 @@
-# Information about the terminal
+# Conversion
 
-## 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.
+## Convert a hex color to RGB
 
 **Example Function:**
 
 ```sh
-get_term_size() {
-    # Usage: get_term_size
+hex_to_rgb() {
+    # 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
-    # exported immediately.
-    shopt -s checkwinsize; (:;:)
-    printf '%s\n' "$LINES $COLUMNS"
+    printf '%s\n' "$r $g $b"
 }
 ```
 
 **Example Usage:**
 
 ```shell
-# Output: LINES COLUMNS
-$ get_term_size
-15 55
+$ hex_to_rgb "#FFFFFF"
+255 255 255
 ```
 
-## Get the terminal size in pixels
 
-**CAVEAT**: This does not work in some terminal emulators.
+## Convert an RGB color to hex
 
 **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]}"
+rgb_to_hex() {
+    # Usage: rgb_to_hex "r" "g" "b"
+    printf '#%02x%02x%02x\n' "$1" "$2" "$3"
 }
 ```
 
 **Example Usage:**
 
 ```shell
-# Output: WIDTHxHEIGHT
-$ get_window_size
-1200x800
-
-# Output (fail):
-$ get_window_size
-x
+$ rgb_to_hex "255" "255" "255"
+#FFFFFF
 ```
 
-## Get the current cursor position
 
-This is useful when creating a TUI in pure bash.
+# Code Golf
 
-**Example Function:**
+## Shorter `for` loop syntax
 
-```sh
-get_cursor_pos() {
-    # Usage: get_cursor_pos
-    IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
-    printf '%s\n' "$x $y"
+```shell
+# Tiny C Style.
+for((;i++<10;)){ echo "$i";}
+
+# Undocumented method.
+for i in {1..10};{ echo "$i";}
+
+# Expansion.
+for i in {1..10}; do echo "$i"; done
+
+# C Style.
+for((i=0;i<=10;i++)); do echo "$i"; done
+```
+
+## Shorter infinite loops
+
+```shell
+# Normal method
+while :; do echo hi; done
+
+# Shorter
+for((;;)){ echo hi;}
+```
+
+## Shorter function declaration
+
+```shell
+# Normal method
+f(){ echo hi;}
+
+# Using a subshell
+f()(echo hi)
+
+# Using arithmetic
+# You can use this to assign integer values.
+# Example: f a=1
+#          f a++
+f()(($1))
+
+# Using tests, loops etc.
+# NOTE: You can also use ‘while’, ‘until’, ‘case’, ‘(())’, ‘[[]]’.
+f()if true; then echo "$1"; fi
+f()for i in "$@"; do echo "$i"; done
+```
+
+## Shorter `if` syntax
+
+```shell
+# One line
+# Note: The 3rd statement may run when the 1st is true
+[[ "$var" == hello ]] && echo hi || echo bye
+[[ "$var" == hello ]] && { echo hi; echo there; } || echo bye
+
+# Multi line (no else, single statement)
+# Note: The exit status may not be the same as with an if statement
+[[ "$var" == hello ]] && \
+    echo hi
+
+# Multi line (no else)
+[[ "$var" == hello ]] && {
+    echo hi
+    # ...
 }
 ```
 
-**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
-# Output: X Y
-$ get_cursor_pos
-1 8
+# Modified snippet from Neofetch.
+case "$OSTYPE" in
+    "darwin"*)
+        : "MacOS"
+    ;;
+
+    "linux"*)
+        : "Linux"
+    ;;
+
+    *"bsd"* | "dragonfly" | "bitrig")
+        : "BSD"
+    ;;
+
+    "cygwin" | "msys" | "win32")
+        : "Windows"
+    ;;
+
+    *)
+        printf '%s\n' "Unknown OS detected, aborting..." >&2
+        exit 1
+    ;;
+esac
+
+# Finally, set the variable.
+os="$_"
 ```
 
 <!-- CHAPTER END -->