linux命令实现:write

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write:用于终端之间的用户通信。

write [username] [终端]

代码实现

#include<stdio.h>#include<stdlib.h>#include<termios.h>#include<unistd.h>#include<utmp.h>#include<fcntl.h>#include<string.h>#include<malloc.h>#define PATH "/var/run/utmp"#define PREPATH "/dev/"char BUF[4096];char *getpath(char *);void write_p(char *); int main(int ac,char **av){if(ac != 2&&ac != 3){return ;}char *str;if(ac == 2){str = getpath(av[1]);write_p(str);return ;}if(find(av[2],av[1])) {printf("%s is not login this \n",av[1]);return;}write_p(av[2]);}char *getpath(char *name)//return stt* pts/*{if(name == NULL) return NULL;struct utmp p;char *str = (char *)malloc(sizeof(char)*UT_LINESIZE);int fp;ssize_t rd;if((fp = open(PATH,O_RDONLY)) == -1){perror(PATH);exit(-1);}while((rd = read(fp,&p,sizeof(struct utmp))) != 0){if(rd == -1){perror(PATH);exit(-1);}if(strcmp(name,p.ut_user) == 0) strcpy(str,p.ut_line);}if(strlen(str) == 0) {printf("no login\n");exit(-1);}return str;}void write_p(char *path){int fp;ssize_t rd;char str[256];strcpy(str,PREPATH);strcat(str,path);if((fp = open(str,O_WRONLY)) == -1){perror(str);exit(-1);}while(fgets(BUF,4096,stdin) != NULL){if(write(fp,BUF,strlen(BUF)) == -1){perror(str);exit(-1);}}return ;}int find(char *path,char *name){int fp;ssize_t rd;struct utmp x;if((fp = open(PATH,O_RDONLY)) == -1){perror(PATH);exit(-1);}while((rd = read(fp,&x,sizeof(struct utmp))) != 0){if(rd == -1){perror(PATH);exit(-1);}if(strcmp(path,x.ut_line) == 0 && strcmp(name,x.ut_user) == 0) return 0;}return 1;}

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