Can't execute console commands in C with fork and pipe - c

Question

I'm trying to make program on C, which execute console shell command
cat log.txt| awk '{ print $7 }' | head -10
but the third command won't work with 2 present.
Here's what i done
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main()
{
int fd[2], status;
pipe(fd);
pid_t pid1 = fork();
if (!pid1)
{
dup2(fd[1], 1);
close(fd[0]);
close(fd[1]);
char* command[3] = {"/bin/cat", "log.txt", 0};
execvp(command[0], command);
exit(EXIT_FAILURE);
}
else if (pid1 == -1)
{
fprintf(stderr, "Can't fork, exiting...\n");
exit(EXIT_FAILURE);
}
pid_t pid2 = fork();
if (!pid2) {
dup2(fd[0], 0);
close(fd[0]);
close(fd[1]);
char* command[3] = {"awk", "{ print $7 }", 0};
execvp(command[0], command);
exit(EXIT_FAILURE);
} else if (pid2 == -1) {
fprintf(stderr, "Can't fork, exiting...\n");
exit(EXIT_FAILURE);
}
pid_t pid3 = fork();
if (!pid3) {
dup2(fd[0], 0);
close(fd[0]);
close(fd[1]);
char* command[3] = {"head", "-10", 0};
execvp(command[0], command);
exit(EXIT_FAILURE);
} else if (pid3 == -1) {
fprintf(stderr, "Can't fork, exiting...\n");
exit(EXIT_FAILURE);
}
close(fd[0]);
close(fd[1]);
waitpid(pid1, NULL, 0);
waitpid(pid2, NULL, 0);
waitpid(pid3, &status, 0);
exit(status);
return 0;
}
pid3 can't execute. I tried to make dup2(fd[1], 1) in pid3, but thats doesn't work. What should be on pid3 to make it's work and how to make more than 3 commands using dup2?

Answer 1

You have created one pipe. One pipe has two ends. Two ends are enough for two processes. If you have three processes all in a single pipeline, you need two pipes. The process in the middle holds on two pipes and two other processes hold on the remaining ends.
Look at this picture:
cat | awk | head
See two pipe symbols? They are the two pipes you need.

Answer 2

You will have to set up two pipes-- one to connect cat to awk and one to connect awk to head.
Also, don't close file descriptors that you actually need (such as fd[0] in your first fork!)