Added build files to turn the bible into a book

manuscript/chapter10.txt

@@ -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
-# Simple math
-((var=1+2))
-
-# Decrement/Increment variable
-((var++))
-((var--))
-((var+=1))
-((var-=1))
-
-# Using variables
-((var=var2*arr[2]))
+# Clear screen on script exit.
+trap 'printf \\e[2J\\e[H\\e[m' EXIT
 ```
 
-## Ternary tests
+## Ignore terminal interrupt (CTRL+C, SIGINT)
 
 ```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))
+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 -->