Character classes

Character classes, also known as a character set, is a regular expression consisting of a group of characters enclosed in brackets. It matches any one of the enclosed characters, irrespective of the order of occurrence of that character in the bracket. For example, [abcdefgh] matches any of the a, b, c, d, e, f, g, or h characters. 

In the following example, we print the employee information for those whose names begin with any of the characters enclosed within brackets:

$ awk '/^[ ABCDEFGHIJ ]/{ print }' emp.dat

The output on execution of the given code is as follows:

Jack    Singh   9857532312  jack@gmail.com      M   hr      2000Jane    Kaur    9837432312  jane@gmail.com      F   hr      1800Eva     Chabra  8827232115  eva@gmail.com       F   lgs     2100Amit Sharma 9911887766 ...

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