a C program (time_shm.c) that determines the amount of time necessary to run a command from the command line.

This program will be run as ./time and will report the amount of elapsed time to run the specified command

This will involve using fork() and execvp() functions, as well as the gettimeofday() function to determine the elapsed time.

time_shm.c, will have the child process write the starting time to a region of shared memory before it calls execvp(). After the child process terminates, the parent will read the starting time from shared memory. The region of shared memory should be established before the child process is forked, allowing both the parent and child processes access to the region of shared memory

You will use the gettimeofday() function to record the current timestamp. This function is passed a pointer to a struct timeval object, which contains two members: tv_sec and tv_usec. These represent the number of elapsed seconds and microseconds since January 1, 1970 (known as the UNIX EPOCH). The following code sample illustrates how this function can be used:

// Get current time timeval_t startTime; gettimeofday( &startTime, 0 );

// get the end time timeval_t end_time; gettimeofday( &end_time, 0 );

// calculate elapsed time timeval_t elapsed_time; timersub( &end_time, startTime, &elapsed_time );

// print elapsed time (microseconds right justified zero filled) printf( " Elapsed time: %d.%06d seconds ", elapsed_time.tv_sec, elapsed_time.tv_usec );