sane7222 / mini-utilities

Project 1: Mini Unix Utilities

Introduction This project should be programmed entirely in C and must compile and run on standard Linux environments. In this assignment, you will build a set of simplified Linux utilities: cat, sed, and uniq. We will use slightly different names for the utilities in this assignment to avoid confusion - my-cat, my-sed, and my-uniq.

Summary of what gets turned in:

• Bunch of .c files, one each for a utility: my-cat.c, my-sed.c, my-uniq.c. – Each should compile successfully with the -Wall and -Werror flags. – Each should pass tests we supply.

• You must supply a Makefile to compile your source.

• Include a single README.md for all the files describing your implementation.

• Assume that input files for each utility can be larger than RAM available on system.

1. my-cat The program my-cat is a simple program. Generally, it reads a file as specified by the user and prints its contents. A typical usage is as follows, in which the user wants to see the contents of main.c, and thus types: prompt> ./my-cat main.c #include <stdio.h> ...

As shown, my-cat reads the file main.c and prints out its contents. To create the my-cat binary, youll be creating a single source file, my-cat.c, and writing a little C code to implement this simplified version of cat. To compile this program, you will do the following: prompt> gcc -o my-cat my-cat.c -Wall -Werror

This will make a single executable binary called my-cat which you can then run as above. You’ll need to learn how to use a few library routines from the C standard library (often called libc) to implement the source code for this program, which we’ll assume is in a file called my-cat.c. All C code is automatically linked with the C library, which is full of useful functions you can call to implement your program.

For this project, we recommend using the following routines to do file input and output: fopen(), fgets(), and fclose(). On UNIX systems, the best way to read about such functions is to use what are called the man pages (short for manual). To access the man page for fopen(), for example, just type the following at your UNIX shell prompt: prompt> man fopen

Here is a typical usage of fopen(): FILE *fp = fopen("main.c", "r"); if (fp == NULL) { printf(‘‘cannot open file \n’’); exit(1); }

Thus, as the code above does, please check that fopen() does not return NULL before trying to use the FILE pointer it returns. Third, note that when the error case occurs, the program prints a message and then exits with error status of 1. In UNIX systems, it is traditional to return 0 upon success, and non-zero upon failure. Here, we will use 1 to indicate failure.

Side note: if fopen() does fail, there are many reasons possible as to why. You can use the functions perror() or strerror() to print out more about why the error occurred.

Once a file is open, there are many different ways to read from it. We suggest you use fgets() for this part of the project. fgets() is used to get input from files, one line at a time. To print out file contents, just use printf(). For example, after reading in a line with fgets() into a variable buffer, you can just print out the buffer as follows: printf("%s", buffer);

Note that you should not add a newline (\n) character to the printf(), because that would be changing the output of the file to have extra newlines. Just print the exact contents of the read-in buffer (which, of course, many include a newline). Finally, when you are done reading and printing, use fclose() to close the file (thus indicating you no longer need to read from it).

More Details:

• Your program my-cat can be invoked with one or more files on the command line; it should just print out each file in turn.

• In all non-error cases, my-cat should exit with status code 0, usually by returning a 0 from main() (or by calling exit(0)).

• If no files are specified on the command line, my-cat should just exit and return 0. Note that this is slightly different than the behavior of normal UNIX cat.

• If the program tries to fopen() a file and fails, it should print the exact message “my- cat: cannot open file” (followed by a newline) and exit with status code 1. If multiple files are specified on the command line, the files should be printed out in order until the end of the file list is reached or an error opening a file is reached (at which point the error message is printed and my-cat exits).

2. my-sed The second utility you will build is called my-sed, a variant of the GNU/Linux utility called sed or streaming editor. For all purposes sed is the command line version of find and replace, the power of sed comes from matching regular expressions. Using regexs you don’t just match strings but any possible pattern. But thankfully my-sed will only be used to find and replace it with the exact given string. It will find the first instance of a string in a line and substitute it with another. It will print the output to standard output. Instances following the first instance remain as is. My-sed does not change input files.

In case there is no candidate to substitute the line will be printed as is. Here is how a user will substitute word the foo with bar from baz.txt and qux.txt. prompt>./my-sed foo bar baz.txt qux.txt

More details:

• Your program is passed a find term, a replace term, and arbitrary number of input files.

• If an empty string ("") is specified as the replace term, then instead of replacing, the search term should be deleted (don’t substitute a space).

• The matching is case sensitive. So foo will not match with Foo.

• The find and replace terms will not contain any escape characters like \n or \0.

• The lines can be arbitrarily long (that is, you may see many many characters before you encounter a newline character, \n). my-sed should work as expected even with very long lines. For this, you might want to look into the getline() library call (instead of fgets()), or roll your own.

• If the my-sed is passed with no command line arguments or if any of the manda- tory arguments are missing it should print “my-sed: find term replace term [file ...]” (followed by a newline) and exit with status code 1. Example of such inputs – prompt> ./my-sed prompt> ./my-sed foo

• If my-sed encounters a file that it can’t open it should print “my-sed: cannot open file” (followed by a newline) and exit with status code 1 immediately.

• If no input file is specified, my-sed should work but instead of reading from a file, my-sed should read from standard input. Doing so is easy because the file stream stdin is already open; you can use fgets() (or similar routines) to read from it. Following are different ways my-sed can be executed:

• In the following case term foo will be removed from bar.txt. prompt> ./my-sed foo "" bar.txt

• In the following case word foo will be replaced with bar.txt taking the input from stdin. prompt> ./my-sed foo bar.txt

• In the following case replace foo.txt with bar.txt in baz.txt. prompt>./my-sed foo.txt bar.txt baz.txt

• In the following case replace foo.txt with bar.txt taking input from stdin. prompt> ./my-sed foo.txt bar.txt

• On the other hand if the input to my-sed is the following prompt> ./my-sed foo.txt The output should be– my-sed: find_term replace_term [file ...]

• The above examples should have given you an idea exactly when your program should throw an error.

3. my-uniq The last utility you will build is called my-uniq, a version of the Unix utility uniq. The original Unix uniq utility detects adjacent duplicate lines from the input file and removes them and writes out to an output file. my-uniq will do exactly this, it finds out adjacent duplicate lines in files, and prints them. For example, consider the following command: prompt>./my-uniq foo.txt bar.txt

This will read contents from file foo.txt and bar.txt, delete adjacent duplicate lines from each of them and print the output to shell.

More details:

• If my-uniq encounters a file that it can’t open it should print. “my-uniq: cannot open file” (followed by a newline) and exit with status code 1 immediately.

• my-uniq should accept an arbitrary number of files as input and print the output to standard output. However, it should only detect duplicates within each file. For example, if the first line in the second file is the same as the last line in the first file, it should not be removed.

• The input file can be really large as well as each line can be arbitrarily long.

• The input file should not be modified.

• If no files are specified, my-uniq should read from standard input.

Deliverables:

• Please submit your deliverables using Canvas before 11:59pm on the due date. • Please include all files (including Makefiles and source code) necessary for a successful build as a zip file. • The name of your submission should be cs460-project1.zip.

Grading: Your submission will be graded by compiling and running it.

• Please make sure your source code can compile. Absolutely no credit if it does not compile. • Please make sure your programs run ocan standard Linux servers. • Please don’t include the binary files. Do a make clean before submission. • Please don’t leave out any files! • Please don’t modify any files you don’t need to! • Please don’t send us the meta-information from your revision control system!