Added build files to turn the bible into a book

manuscript/chapter13.txt

@@ -0,0 +1,52 @@
+# Obsolete Syntax
+
+## Shebang
+
+Use `#!/usr/bin/env bash` instead of `#!/bin/bash`.
+
+- The former searches the user's `PATH` to find the `bash` binary.
+- The latter assumes it is always installed to `/bin/` which can cause issues.
+
+```shell
+# Right:
+
+    #!/usr/bin/env bash
+
+# Wrong:
+
+    #!/bin/bash
+```
+
+## Command Substitution
+
+Use `$()` instead of `` ` ` ``.
+
+```shell
+# Right.
+var="$(command)"
+
+# Wrong.
+var=`command`
+
+# $() can easily be nested whereas `` cannot.
+var="$(command "$(command)")"
+```
+
+## Function Declaration
+
+Don't use the `function` keyword, it reduces compatibility with older versions of `bash`.
+
+```shell
+# Right.
+do_something() {
+    # ...
+}
+
+# Wrong.
+function do_something() {
+    # ...
+}
+```
+
+<!-- CHAPTER END -->
+