C++ 如何用c语言修改shadow文件hash部分(编程)

下面的代码是我需要的全部.

1:我根据关键参数找到了具体的行. 2:我倒回文件指针 3:读取除特定行外的所有字符并写入副本文件. 4:重命名副本文件名.

const char* filename="/etc/shadow_old";  //just change shadow_old to shadow.

const char* filenameReplica="/etc/shadow_replica";

int renamePassword(const char* key,const char* value){

    system("cp /etc/shadow /etc/shadow_old");
    
    FILE* shadow = fopen(filename,"r+");
    FILE* replica = fopen(filenameReplica,"w");;
    if (shadow == NULL  || replica == NULL)
        {
            printf ("Cannot open shadow file \n");
            return -1;
        }

    

    int lineCounter=1;
    int lineNumber=0;

    char * line = NULL;
        size_t len = 0;
        char* delimiter= ":";
        ssize_t read;
        int ret = 0;
        char* pch = NULL;
    char* token = NULL;
    short userFound=0;
    
    while ((read = getline(&line, &len, shadow)) != -1)
        {
        pch = NULL;
            pch = strstr(line, key);
        
            if(pch)
        {   
            lineNumber=lineCounter;
            userFound=1;
        }else lineCounter++;
    }

    char ch='A';
    int tmp=1;
    rewind(shadow);
    while((ch =getc(shadow))!=EOF){
        //ch =getc(shadow);
        //printf("ch: %c\n",ch);
        if(tmp != lineNumber)
        {
            putc(ch,replica);
        }
        if(ch=='\n')
        {   
            tmp++;
        }
    }

    int lenOfReplacement=strlen(value); 
    int lenOfKey = strlen(key);
    char* tmpValue=(char*) malloc (lenOfKey+lenOfReplacement+1);
    strncpy(tmpValue,key,lenOfKey);
    strncpy(tmpValue + lenOfKey,value,lenOfReplacement);
    tmpValue[lenOfKey+lenOfReplacement+1]='\0';

    printf("tmpValue-->  %s\n",tmpValue);
    //fwrite("\n",1,strlen("\n"),replica); //uncomment this line if you want to change multiple user not only one user. this line create new line in shadow file(no bad effect).
    fwrite(tmpValue,1,strlen(tmpValue),replica);
    free(tmpValue);
    

    fclose(shadow);
    fclose(replica);
    remove(filename);
    rename(filenameReplica,filename);
    
    return 0;
}