Added section for =~ operator

bash.html.markdown

@@ -161,6 +161,16 @@ then
     echo "This will run if $Name is Daniya OR Zach."
 fi
 
+# There is also the =~ operator, which tests a string against a Regex pattern:
+Email=me@example.com
+if [[ "$Email" =~ [a-z]+@[a-z]{2,}\.(com|net|org) ]]
+then
+    echo "Valid email!"
+fi
+# Note that =~ only works within double [[ ]] square brackets,
+# which are subtly different from single [ ].
+# See the appropriate [manual section](http://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs) for more on this.
+
 # Expressions are denoted with the following format:
 echo $(( 10 + 5 )) # => 15