linux tail源码

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>

void tail_file(const char *filename, int lines) {
    FILE *file = fopen(filename, "r");
    if (!file) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    // 定位到文件末尾
    fseek(file, 0, SEEK_END);

    // 读取并显示内容
    char buffer[1024];
    long pos = ftell(file);
    int count = 0;
    while (pos > 0 && count < lines) {
        pos--;
        fseek(file, pos, SEEK_SET);
        int ch = fgetc(file);
        if (ch == '
') {
            count++;
        }
        if (count == lines) {
            break;
        }
    }

    // 显示剩余内容
    while ((ch = fgetc(file)) != EOF) {
        putchar(ch);
    }

    fclose(file);
}

int main(int argc, char *argv[]) {
    if (argc < 2) {
        fprintf(stderr, "Usage: %s <filename> [-n <lines>]
", argv[0]);
        return EXIT_FAILURE;
    }

    const char *filename = argv[1];
    int lines = 10; // 默认显示10行
    if (argc == 4 && strcmp(argv[2], "-n") == 0) {
        lines = atoi(argv[3]);
    }

    tail_file(filename, lines);
    return EXIT_SUCCESS;
}