Question

Write a C program for Linux called pipes.c that does the following:

In the main() function, it creates a pipe using the pipe() function, then creates two child processes with

fork(). Child 1 redirects stdout to the write end of the pipe and then executes with execlp() the "ps -aux"

command. Child 2 redirects its input from stdin to the read end of the pipe, then it executes the "sort -r

-n -k 5" command.

After creating both children, the parent process waits for them to terminate before it can exit.

Note that you may have to create Child 2 first, followed by Child 1.

The parent program does the same thing as a shell that runs the command "ps -aux | sort -r -n -k 5".

You must use the fork(), pipe(), dup2(), close(), execlp() functions.

Answer 1

solution:

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
int main(void)
{
int fd[2], nbytes;
pid_t childpid;
char string[] = "Hello, world!\n";
char readbuffer[80];
pipe(fd);
if((childpid = fork()) == -1)
{
perror("fork");
exit(1);
}
if(childpid == 0)
{
/* Child process closes up input side of pipe */
close(fd[0]);
/* Send "string" through the output side of pipe */
write(fd[1], string, (strlen(string)+1));
exit(0);
}
else
{
/* Parent process closes up output side of pipe */
close(fd[1]);
/* Read in a string from the pipe */
nbytes = read(fd[0], readbuffer, sizeof(readbuffer));
printf("Received string: %s", readbuffer);
}
return(0);
}