自己动手写shell命令之write
Linux下write命令同意用户跟其它终端上的用户对话。用c语言实现shell命令write。代码例如以下:
#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; }