This is in Unix

Problem 3 (14 points): Answer the following questions about regular expressions: a) A regular expression is a that can be specified to perform advanced searches. b) Thecommand performs searches for text using simple regular expression rules. c) Give the command to search the file 'usernames.txt' for all lines ending with goodbye' or 'later or 'farewell' Give regular expressions (such that could be used with grep and egrep) for each of the following: d) All lines beginning with the phrase 'Unix is' e) All lines that end in either 'a, 'b', or c' fAll lines that contain the word 'result' followed by any three numbers ) All lines that contain either 0 or 1 instances of the character 'x', but no more h) All ines that contain a word with 0 or more of the letter 'a', followed by 1 or more of the letter 'b', followed by 0 or 1 letter 'c