Here is another excellent tutorial from Nixcraft
How do I use the Grep command with regular expressions under Linux operating systems?
Linux comes with GNU grep, which supports extended regular expressions. GNU grep is the default on all Linux systems. The grep command is used to locate information stored anywhere on your server or workstation.
Regular Expressions is nothing but a pattern to match for each input line. A pattern is a sequence of characters. Following all are examples of pattern:
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