Hello,
I want to redirect stdin and stdout of "cat" program to my program.
For example if I type "cat" in terminal, and enter input and press enter it outputs the same string I entered.
In my c program I am trying to use pipes and dup. I cannot figure out why it is not working.
When I launch it, it exits without reading stdout of "cat".
Here is what I have so far:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#define STDIN fileno(stdin)
#define STDOUT fileno(stdout)
#define STDERR fileno(stderr)
int main(int argc, char *argv[]){
int p2c[2] = {-1, -1}; /* parent -> child */
int c2p[2] = {-1, -1}; /* child -> parent */
pid_t childpid; /* child process id */
if (pipe(p2c) < 0 || pipe(c2p)){
/* Error establishing pipes */
} else {
#define CHILDREAD p2c[0]
#define CHILDWRITE c2p[1]
#define PARENTREAD c2p[0]
#define PARENTWRITE p2c[1]
childpid = fork();
if (childpid == 0) {
/* Child process */
close(PARENTWRITE);
close(PARENTREAD);
dup2(CHILDREAD, STDIN);
dup2(CHILDWRITE, STDOUT);
close(CHILDREAD);
close(CHILDWRITE);
execv("cat", NULL);
} else {
/* Parent process */
close(CHILDREAD); close(CHILDWRITE);
char *writing = "BLAHHHHH\n";
char *reading = calloc(strlen(writing), sizeof(char));
write(PARENTWRITE, writing, strlen(writing));
read(PARENTWRITE, reading, strlen(reading));
printf("Parent read from child: %s\n",reading);
close(PARENTWRITE); close(PARENTREAD);
wait(NULL);
}
}
return 0;
}Thanks for your help!!!