自己动手写shell命令之write

#include	<stdio.h>
#include	<fcntl.h>
#include	<unistd.h>
#include	<utmp.h>
#include	<pwd.h>
#include	<sys/types.h>
#include	<stdlib.h>
#include	<sys/stat.h>
#include	<time.h>

char * get_terminal_name(char *);
char * get_terminal_name_by_user_name(char *);
void hello();

int main(int argc, char * argv[]) {
int fd;
char buffer[1024];
char * terminal_name;
if (argc != 2) {
printf("write usage: write [ttyname|username]");
return 1;
}
terminal_name = get_terminal_name(argv[1]);
if(terminal_name == NULL)
{
printf("get terminal name error\n");
return 1;
}
//printf("terminate_name:%s", terminal_name);

fd = open(terminal_name,O_WRONLY);
hello(fd);

while(fgets(buffer,1024,stdin) != EOF)
{
write(fd,buffer,strlen(buffer));
}
close(fd);
return 0;
}

void hello(int fd) {
char greeting[1024];
struct passwd * passwd_pointer;
time_t now;
char host[255];
gethostname(host, 255);
time(&now);
passwd_pointer = getpwuid(getuid());
sprintf(greeting, "Message from %s@%s on %s at %5.5s ...\n",
passwd_pointer->pw_name, host, ttyname(0), ctime(&now) + 11);
write(fd,greeting,strlen(greeting));
}

char * get_terminal_name(char * user_input) {
char terminal_name[255];
struct stat stat_buffer;
if (lstat(user_input, &stat_buffer) != -1) {
if (S_ISCHR(stat_buffer.st_mode)) {
return user_input;
}
}
return get_terminal_name_by_user_name(user_input);
}

char * get_terminal_name_by_user_name(char * user_name) {
struct utmp * utmp_pointer;
setutent();
int number = 0;
char * result = (char *) malloc(sizeof(char) * 255);
char *mytty = ttyname(0); /* begins "/dev/" */
char *ttydev = mytty + strlen("/dev/");
printf("%s\n", mytty);

while ((utmp_pointer = getutent()) != NULL) {
if (strcmp(user_name, utmp_pointer->ut_user) == 0
&& utmp_pointer->ut_type == USER_PROCESS
&& strcmp(utmp_pointer->ut_line, ttydev) != 0
&& utmp_pointer->ut_line[0] != ':') {
number++;
//printf("%s\n", utmp_pointer->ut_line);
if (number == 1) {
strcpy(result, "/dev/");
strcat(result, utmp_pointer->ut_line);
}
}
}
endutent();
if (number > 1)
printf("warning:%s is logged in %d different terminals,using %s\n",
user_name, number, result);
if(number == 0)
return NULL;
return result;
}