Miscellaneous improvements

manuscript/chapter18.txt

@@ -95,16 +95,16 @@ f()for i in "$@"; do echo "$i"; done
 ```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
+[[ $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 ]] && \
+[[ $var == hello ]] &&
     echo hi
 
 # Multi line (no else)
-[[ "$var" == hello ]] && {
+[[ $var == hello ]] && {
     echo hi
     # ...
 }