Added introduction.

manuscript/chapter9.txt

@@ -1,30 +1,41 @@
-# Arithmetic
+# Brace Expansion
 
-## Simpler syntax to set variables
+## Ranges
 
 ```shell
-# Simple math
-((var=1+2))
+# Syntax: {<START>..<END>}
 
-# Decrement/Increment variable
-((var++))
-((var--))
-((var+=1))
-((var-=1))
+# Print numbers 1-100.
+echo {1..100}
 
-# Using variables
-((var=var2*arr[2]))
+# Print range of floats.
+echo 1.{1..9}
+
+# Print chars a-z.
+echo {a..z}
+echo {A..Z}
+
+# Nesting.
+echo {A..Z}{0..9}
+
+# Print zero-padded numbers.
+# CAVEAT: bash 4+
+echo {01..100}
+
+# Change increment amount.
+# Syntax: {<START>..<END>..<INCREMENT>}
+# CAVEAT: bash 4+
+echo {1..10..2} # Increment by 2.
 ```
 
-## Ternary tests
+## String Lists
 
 ```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))
+echo {apples,oranges,pears,grapes}
+
+# Example Usage:
+# Remove dirs Movies, Music and ISOS from ~/Downloads/.
+rm -rf ~/Downloads/{Movies,Music,ISOS}
 ```
 
 <!-- CHAPTER END -->