while(1) {
    bool czyczekac = true;

    ...

    if(read_line[length-2]=='&') {
        czyczekac = false;
        read_line[length-2]='\0'
;   }

    ...

    int pid = fork();
    if(pid == 0) {
        execvp(progpath, argv);
        fprint(stderr, "Couldn execvp\n");
        exit(EXIT_FAILURE);
    } else {
        if(czyczekac) {
            wait();
        }
    }
}