Description
Write a Linux utility program. Required Reading None, but you may find the links to the C language and C library documentation helpful.
Instructions
For this programming assignment you are going to implement a simple C version of the UNIX cat program called kitten. The cat program allows you to display the contents of one or more text files. The kitten program will only display one file. The correct usage of your program should be to execute it on the command line with a single command line argument consisting of the name you want to display.
However, your program should also respond well when it is used incorrectly. Processing Command-Line Arguments Unless you have done Linux programming before you probably haven’t needed to process command line arguments. A typical C program has a main function that looks like this: in t main () { // body of main function } This works just fine if your program does not take any command line arguments. If it does, as is the case with kitten, you will need access to those arguments. You will need to write your main function like this: in t main ( in t argc , char * argv []) { // body of main function }
1 The argc parameter is the number of command line arguments provided to the program including the name of the command itself. The kitten program should have two command line arguments if it is used correctly: the name of the command and the file to display. The argv parameter is an array of C-strings, or nullterminated character arrays. This means that argv[0] is the name of the program, argv[1] is the first command line argument, argv[2] is the second command line argument, and so on. The kitten program should display a usage message to standard error and exit the program using exit(1) if argc is anything other than 2. Otherwise it should use the C-string contained in argv[1] as the name of the input file to open. Note that exit function requires the following preprocessor statement: #inc lude < stdlib .h > Streams The standard way to deal with files, the console, and other sources of input and output is by using streams. For historical reasons, the data type used to deal with a stream, whether or not it uses a file, is FILE *. Working with streams requires the following preprocessor statement: #inc lude < stdio .h >
To declare a stream variable use the FILE * data type: FILE * stream ; To open a file use the fopen function: stream = fopen ( filename , opentype ); • fopen has two parameters: filename is the name of the input file as a C-string, and opentype is a C-string containing information about how the file is to be opened. • If the file is to be opened for reading only, the second argument should be “r”. • fopen returns a value of type FILE * if the file opened successfully, and NULL otherwise. • If your program can not open the file, display a message that the file was not found to standard error and exit the program. To read a single character from a file, use the fgetc function: character = fgetc ( stream ); • fgetc has one parameter: the stream that was returned by fopen. • fgetc returns the character read if it was successful and the special EOF character if it was not successful. To close a file use the fclose function: fclose ( stream ); • fclose has one parameter: the stream representing the file to be closed. • fclose returns 0 if the file closed correctly and EOF if it did not. The latter case is rare, so the return value is typically ignored. 2 To write a string to standard output use the puts function: puts ( string ); • puts has one parameter: the C-string to be printed. Note that if you want a newline to be displayed you have to use the special character \n at the end of the string. • puts returns a non-negative value if successful and EOF if unsuccessful. The return value is typically ignored.
• You will not need this function for this assignment, but it may be helpful to you for debugging purposes. To write a string to standard error use the fputs function: fputs ( string , stream ); • fputs has two parameters: string is the C-string to be printed, and stream is the stream representing the destination of the output. • To print to standard error, use stderr as the second argument. • fputs returns a non-negative value if successful and EOF if unsuccessful. The return value is typically ignored. To write a single character to the console use the putchar function: putchar ( character ); • putchar takes a single argument: the character to be printed. • putchar returns the character if it printed successfully and EOF if it does not. The return value is typically ignored. Linux Development Tools You should not be using Windows development tools for this class! Instead, you should use the development tools provided on the Linux server. Writing Your Code The best way to write a Linux program is to use one of the many text editors provided on a typical Linux distribution. If you are using the Linux server you have several options, but the nano text editor mentioned in Assignment 1 is probably the simplest. If you want to use a text editor with more features for writing source code you can try using vim (see Chapter 6 of the Linux book) or emacs (see Chapter 7 of the Linux book.)
Compiling Your Code Your source file should be called yourlastnameAssign2.c except with your actual last name. To compile this code you should use the gcc compiler on the Linux server. To create an executable file called kitten use the following command: gcc -o kitten yourlastnameAssign2.c If your program compiled, you should see an entry for kitten when you execute the ls command. 3 Running Your Code Since your home directory on the Linux server is not in your execution path, you will need to specify the file you are executing directly by putting a ./ before the name of the executable.
Here are some examples of what several runs should look like: $ ./kitten foo.txt This is a text file that I created in a text editor in order to test out the kitten program. $ ./kitten usage: kitten $ ./kitten foo.txt otherFile.txt usage: kitten $ ./kitten no_such_file.txt error: file not found What to Hand In Download the source file yourlastnameAssign2.c to your local machine, then upload it to D2L in the dropbox called Assignment 2. 4
