Question

如何确定新数据是否已写入日志文件以及如何提取这些新数据并将其写入另一个文件？

我的目标是为调试目的创建一个大日志文件，因为当文件达到特定大小时，当前日志文件总是删除数据。

我唯一的想法是每隔几分钟从旧日志文件创建一个副本。

Answer 1

快速＆amp;脏的方法是在控制台中键入以下行 - 用实际路径和日志文件替换“path / to / ...”和“other / path / ...”：

* * * * * /path/to/small_file.log >> /other/path/to/big_file.log

每次写入都不会执行IO，但它会每分钟执行一次，这可能会或可能不足以满足您的需求。

编辑：尝试使用C找到更好的方法，这是我到目前为止所得到的内容（请阅读我在帖子中的评论以获取更多信息）。

//Include the full pathname and file for LOG_BIG and LOG_SMALL
#define LOG_BIG "/var/.../log_example_big.txt"
#define LOG_SMALL "/var/.../log_example_small.txt"
//FIXME: change LOG_BIG and LOG_SMALL to match the locations of the logfiles

#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <math.h>
#include <sys/types.h>

time_t last_mod_time(const char *path);


int main(int argc, const char * argv[]) {
    char outstr[200];
    time_t t;
    struct tm *tmp;

    t = time(NULL);
    tmp = localtime(&t);

    // check for local time set failure
    if (tmp == NULL) {
        perror("localtime");
        return 0;
    }
    //if the returned size_t for strftime is 0, we exit
    if (strftime(outstr, sizeof(outstr), argv[1], tmp) == 0) {
        fprintf(stderr, "strftime returned 0");
        return 0;
    }
    double diff_log_mod_time;
    // get the difference of last modified time between LOG_BIG and LOG_SMALL
    diff_log_mod_time = difftime(last_mod_time(LOG_BIG),last_mod_time(LOG_SMALL));

    //difference in log modification times should be close to 0 +/- 10 ... I think
    if(fabs(diff_log_mod_time) > 10.0) {

        /* to finish the code, we would need to find the difference between the data in LOG_BIG and LOG_SMALL (assuming that LOG_BIG should contain all of LOG_SMALL and then some) */

    }
    exit(EXIT_SUCCESS);
}

/**
 * last_mod_time - this function finds the last modification time for a filename specified and returns 
 * it in epoch time (seconds lapsed since 1/1/1970)
 */
time_t last_mod_time(const char *path) {
    struct stat statbuf;
    if (stat(path, &statbuf) == -1) {
        perror(path);
        exit(1);
    }
    return statbuf.st_mtime;
}

Answer 2

实现这一目标的另一种快速而肮脏的方法是执行以下操作：

cp /path/to/small_file.log /other/path/to/big_file.log;
nohup tail -f /path/to/small_file.log >> /other/path/to/big_file.log &

将新数据从日志文件追加到另一个文件

2 个答案: