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In this assignment, you are asked to implement functions by chaining the standard Unix utility programs. In particular, you are asked to produce a program that searches an input file, selects the lines that match a given regular expression, and sorts the matched lines in reverse order.

Your program should take three arguments:

You are not expected to implement the specific functions, such as matching a regular expression or sorting the lines in reverse order. Rather, you should be using existing Unix utility programs:

1. grep is a utility program which is a file pattern searcher. It takes one command-line argument (the PATTERN string in our case) and search for matches line by line from the standard input (or the file specified as the second command-line argument). When a match is found (a line that matches with the PATTERN string), the program prints the line to the standard output. The utility program outputs all matched lines.

2. sort is a utility program that sorts the text file by lines. By default, it reads from the standard input and generates the sorted text to the standard output. Use -r option to sort in reverse order. 

3. Your program should use fork and exec system calls to run the utility programs. You should also use pipe and dup/dup2 system calls to connect them, so that, for example, the standard output of the grep program is “piped” to the standard input of the sort program.