Grepping for multiple strings in a file

We will use egrep which accepts a regular expression to grep for multiple strings.

tail -f localhost_access_log.txt | egrep "\" 404|\" 500" 

Here our example looks at logs to see if we got 404 or 500 request.

 "GET /favicon.ico HTTP/1.1" 404 973
 "GET /login.html  HTTP/1.1" 500 1230
 "GET /favicon.ico HTTP/1.1" 404 973