Grepping across multiple fields

Sometimes one needs to get an idea of how a certain value looks across multiple fields—most common are IP/MAC addresses, dates, and formatted messages. For examples, if I want to see all IP addresses mentioned throughout a file or a document, I need to replace the cut command in the previous example by grep -o -E [1-9][0-9]{0,2}(?:\\.[1-9][0-9]{0,2}){3}, where the –o option instructs grep to print only the matching parts—a more precise regex for the IP address should be grep –o –E (?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?), but is about 50% slower on my laptop and the original one works in most practical cases. I'll leave it as an excursive to run this command on the sample file provided with the book.