分类: LINUX
2013-04-26 11:31:05
#include#include #include #include
#include/* * write1.c * * purpose: send messages to another terminal * method: open the other terminal for output then * copy from stdin to that terminal * usage: write1 username */ main( int ac, char *av[] ) { int fd; char buf[BUFSIZ];
char buf_enter[10]; char *get_tty(), *tty_for_user; if ( ac != 2 ){ /* check args */ fprintf(stderr,"usage: write0 logname\n"); exit(1); } tty_for_user = get_tty( av[1] ); /* find user */ if ( tty_for_user == NULL ) {
fprintf(stderr,"\n %s not exist or not login",av[1]); return 1;
} sprintf(buf, "/dev/%s", tty_for_user); /* open device */ fd = open( buf, O_WRONLY ); if ( fd == -1 ){ perror(buf); exit(1); }
sprintf(buf_enter,"\n");
write(fd,buf_enter,strlen(buf_enter)); /* input Enterkey */
while( fgets(buf, BUFSIZ, stdin) != NULL ) /* write to user */ if ( write(fd, buf, strlen(buf)) == -1 ) break; close( fd ); } char * get_tty( char *logname ) /* * purpose: find the tty at which 'logname' is logged in * returns: a string or NULL if not logged in * errors: does not handle multiple logins */ { static struct utmp utrec; int utfd; int namelen = sizeof( utrec.ut_name ); char *retval = NULL ; if ( (utfd = open( UTMP_FILE, O_RDONLY )) == -1 ) /* open utmp */ return NULL; /* look for a line where the user is logged in */ while( read( utfd, &utrec, sizeof(utrec)) == sizeof(utrec) ) if ( strncmp(logname, utrec.ut_name, namelen ) == 0 ) { retval = utrec.ut_line ; break; } close(utfd); /* close & go */ return retval; }