Add quotes to shell script

- Use consistent syntax
- Make it easier to read the example without scrolling

Author: bkmgit

episodes/04-loops.md

@@ -138,12 +138,13 @@ Alternatively, rather than running the loop above on the command line, you can s
 
 ```
 #!/bin/bash
-# This script loops through .txt files, returns the file name, first line, and last line of the file
+# This script loops through .txt files, returns the file name,
+# first line, and last line of the file
 for file in *.txt
 do
-	echo $file
-	head -n 1 $file
-	tail -n 1 $file
+	echo "$file"
+	head -n 1 "$file"
+	tail -n 1 "$file"
 done
 ```