CS4420/5420 Assignment 1 – System Calls solution

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Description

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Program

You are to write a program called “uniq”. The uniq program takes arguments that specify the name of a file
to process, and writes only non-duplicated adjoining lines to the standard output. In other words, it copies
lines from the input file to the output only if a line is not an exact duplicate of the previous line. To perform
useful work, uniq assumes that the file is already sorted, but it isn’t an error if it isn’t.

Your program should work under the version of Unix on pu1, pu2, and the evens lab computers. Except as
noted below, the program must be written in the the C programming language and must be written using
only system calls and you cannot use any character buffers.

The arguments to the program are as follows:
./uniq [-d] infile
Example
For example, if the input to the program is the following file:
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyZ
abcdefghijklmnopqrstuvwxyZ
abcDEFghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
123456789
123456789
12345678
1234567
123456789
The output should be exactly:
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyZ
abcDEFghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
123456789
12345678
1234567
123456789

Requirements

Other than system calls (open(), read(), write(), close(), lseek(), exit()), the only routines that
you can use that you did not write yourself are printf() and perror().

Your program should work for any file, no matter how large it is. Efficiency will be considered in the grading,
so think carefully about the algorithm.

Your program must check the return values of all system calls. Failure to check all return values will result
in lost credit for the assignment. You program should also detect and report other errors, including invalid
arguments.

Your program must support a “-d” option that prints debugging information to the standard error. Do NOT
wait until the last minute to implement this – that’s a waste of your time.

Any solution using a buffer (character array) will receive no credit.
Beware that there is a standard Unix command with the same name that performs the same function; don’t
get them confused. The output from your program should be identical to that of the Unix uniq program.

Extra Credit Ideas

Duplicate the behavior of the standard Unix “uniq” tool by adding the functionality of the “-c” flag (required
for graduate students)

Allow multiple files as arguments.
Support a case-insensitive comparison option using “-i”.
Anything else that you think is useful…

Turn In
The program will be turned in using Github for Education. We’ll talk more about that next week. You must
include a Makefile. Next week, I will provide some additional testing files, until then you should create your
own.