diff --git a/essential/introduction_to_the_commandline.md b/essential/introduction_to_the_commandline.md
index 388c48d..bef8c7d 100644
--- a/essential/introduction_to_the_commandline.md
+++ b/essential/introduction_to_the_commandline.md
@@ -1648,4 +1648,4 @@ Most of these pipes are not actually *useful* but I hope they illustrate the fle
 * find valid mobile phone numbers [based on](https://en.wikipedia.org/wiki/Telephone_numbers_in_Belgium#Mobile_numbers)
 * find valid IP addresses
 * find all ugly filenames and replace with better names (replace with \_)
-* 
+* regex crossword puzzle