I want to execve a bash as a child process in a c program. The bash should essentially be controlled by the parent process: the parent process reads from stdin, stores the read input into a buffer and writes the content of the buffer to the bash through a pipe. The output of the bash is supposed to be passed through another pipe back to the parent process's stdout. For instance: the parent process reads "ls" and gives it to the bash through a pipe and receives the output of the bash through another pipe. I know this program doesn't make sense, because there are better ways to execute ls (or some other program) on behalf of the parent process. I'm actually just trying to understand how piping works and this is the first program that came into my mind. And i can't make this program work. That's what i have so far:
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/wait.h>
int main() {
int pc[2];//"parent to child"-pipe
int cp[2];//"child to parent"-pipe
int status;
char buffer[256];
char eof = EOF;
if (pipe(pc) < 0 || pipe(cp) < 0) {
printf("ERROR: Pipes could not be created\n");
return -1;
}
pid_t child_pid = fork();
if (child_pid == 0) { //child has pid 0, child enters here
close(pc[1]);//close write end of pc
close(cp[0]);//close read end of cp
//redirecting file descriptors to stdin/stdout
dup2(cp[1], STDOUT_FILENO);
dup2(pc[0], STDIN_FILENO);
execve("/bin/bash",NULL,NULL);
} else {//parent enters here
close(cp[1]);//close write end of cp
close(pc[0]);//close read end of pc
//redirecting file descriptors to stdin/stdout
dup2(cp[0], STDOUT_FILENO);
while(1) {
read(STDIN_FILENO, buffer, 3);
write(pc[1], buffer, 3);
}
waitpid(child_pid, &status, 0);
}
return 0;
}
On execution: I type in ls, hit enter, nothing happens, hit enter again, output.
$ ./pipe
ls
bash: line 3: s: command not found
Why is only the character 's' delivered to the bash?
