pipe.c

#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>

#define BUFSIZE 4096

int main(int argc, char const *argv[]) {
	int rc, status, filedes[2];
	pid_t pid;
	if (pipe(filedes) == -1) {
		printf("pipe() error %d\n", errno);
		return 1;
	}

	pid = fork();
	if (pid > 0) {
		// read output
		printf("I am parent %d\n", getpid());

		// hangs if this is commented out!!
		//close(filedes[1]);

		size_t bytesRead;
		char buf[BUFSIZE];
		memset(buf, '\0', BUFSIZE);
		while ((bytesRead = read(filedes[0], buf, BUFSIZE - 1)) > 0) {
			printf("%s", buf);
			memset(buf, '\0', BUFSIZE);
		}

		int status;
		wait(&status);

		
	} else {
		// write output
		printf("I am child %d\n", getpid());
		//close(filedes[0]);

		FILE* fp = popen("ls -l /usr/bin", "r");
		if (fp == NULL) {
			printf("popen() fails %d\n", errno);
			return 1;
		}
		size_t bytesRead;
		char buf[BUFSIZE];
		while ((bytesRead = fread(buf, 1, BUFSIZE, fp)) > 0) {
			// write to pipe 
			write(filedes[1], buf, bytesRead);
		}
		pclose(fp);
		close(filedes[1]);
	}

	return 0;
}