Added build files to turn the bible into a book

manuscript/chapter13.txt

@@ -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.
-- The latter assumes it is always installed to `/bin/` which can cause issues.
+## Get the location to the `bash` binary
 
 ```shell
-# Right:
-
-    #!/usr/bin/env bash
-
-# Wrong:
-
-    #!/bin/bash
+"$BASH"
 ```
 
-## Command Substitution
-
-Use `$()` instead of `` ` ` ``.
+## Get the version of the current running `bash` process
 
 ```shell
-# Right.
-var="$(command)"
+# As a string.
+"$BASH_VERSION"
 
-# Wrong.
-var=`command`
-
-# $() can easily be nested whereas `` cannot.
-var="$(command "$(command)")"
+# As an array.
+"${BASH_VERSINFO[@]}"
 ```
 
-## Function Declaration
-
-Don't use the `function` keyword, it reduces compatibility with older versions of `bash`.
+## Open the user's preferred text editor
 
 ```shell
-# Right.
-do_something() {
-    # ...
-}
+"$EDITOR" "$file"
 
-# Wrong.
-function 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"
 ```
 
 <!-- CHAPTER END -->