Capturing the output of an external program in C

my_popen.c

#include <stdio.h>
#include <unistd.h>

int my_popen(char *cmd, FILE *handles[2]) {
	/* Naming convention: the child's input and output */
	int input[2];
	int output[2];

	pipe(input);
	pipe(output);

	pid_t child_pid = fork();
	if (child_pid == -1) {
		for (int i = 0; i < 2; i++) {
			close(input[i]); close(output[i]); 
		}
		return -1;
	} else if (!child_pid) {
		/* Redirect stdin and stdout to our pipes. */
		dup2(input[0], STDIN_FILENO);
		dup2(output[1], STDOUT_FILENO);

		/* The pipes have to be closed by both the parent and the child. Closing a
		 * file descriptor in the child does not close it in the parent and vice
		 * versa, even though the child inherits the parent's file descriptors.
		 * Hence we close the parents ends of pipes here in the child. */
		close(input[1]);
		close(output[0]);

		/* The second parameter of execlp is argv[0] for the executed program,
		 * hence there's "sh" twice. */
		execlp("sh", "sh", "-c", cmd, (char*)NULL);
		_exit(127);
	} else {
		/* Close the child's ends of pipes. */
		close(input[0]);
		close(output[1]);
	}

	/* For the handles, we use the same convention as pipe(2): handles[1] is the
	 * write end and handles[0] the read end. */
	handles[0] = fdopen(output[0], "r");
	handles[1] = fdopen(input[1], "w");

	return 0;
}

int main(void) {
	FILE *handles[3];
	char buffer[1024];

	if (my_popen("pandoc", handles) == -1) { perror("my_popen"); return -1; }

	fputs("I don't to *emphasize* my role.", handles[1]);
	fclose(handles[1]);

	fread(buffer, 1, 1024, handles[0]);
	fclose(handles[0]);

	puts("pandoc says:");
	puts(buffer);

	return 0;
}