/* tailf.c -- tail a log file and then follow it  
 * Created: Tue Jan  9 15:49:21 1996 by [email protected]  
 * Copyright 1996, 2003 Rickard E. Faith ([email protected])  
 *  
 * Permission is hereby granted, free of charge, to any person obtaining a  
 * copy of this software and associated documentation files (the "Software"),  
 * to deal in the Software without restriction, including without limitation  
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,  
 * and/or sell copies of the Software, and to permit persons to whom the  
 * Software is furnished to do so, subject to the following conditions:  
 *  
 * The above copyright notice and this permission notice shall be included  
 * in all copies or substantial portions of the Software.  
 *  
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR  
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,  
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL  
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR  
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,  
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR  
 * OTHER DEALINGS IN THE SOFTWARE.  
 *   
 * less -F and tail -f cause a disk access every five seconds.  This  
 * program avoids this problem by waiting for the file size to change.  
 * Hence, the file is not accessed, and the access time does not need to be  
 * flushed back to disk.  This is sort of a "stealth" tail.  
 */   
   
#include <stdio.h>   
#include <stdlib.h>   
#include <unistd.h>   
#include <malloc.h>   
#include <sys/stat.h>   
//#include "nls.h"   
#define _(s) s   
   
static size_t filesize(const char *filename)   
{   
    struct stat sb;   
   
    if (!stat(filename, &sb)) return sb.st_size;   
    return 0;   
}   
   
static void tailf(const char *filename, int lines)   
{   
    char **buffer;   
    int  head = 0;   
    int  tail = 0;   
    FILE *str;   
    int  i;   
   
    if (!(str = fopen(filename, "r"))) {   
    fprintf(stderr, _("Cannot open \"%s\" for read\n"), filename);   
    perror("");   
    exit(1);   
    }   
   
    buffer = malloc(lines * sizeof(*buffer));   
    for (i = 0; i < lines; i++) buffer[i] = malloc(BUFSIZ + 1);   
   
    while (fgets(buffer[tail], BUFSIZ, str)) {   
    if (++tail >= lines) {   
        tail = 0;   
        head = 1;   
    }   
    }   
   
    if (head) {   
    for (i = tail; i < lines; i++) fputs(buffer[i], stdout);   
    for (i = 0; i < tail; i++)     fputs(buffer[i], stdout);   
    } else {   
    for (i = head; i < tail; i++)  fputs(buffer[i], stdout);   
    }   
    fflush(stdout);   
   
    for (i = 0; i < lines; i++) free(buffer[i]);   
    free(buffer);   
}   
   
int main(int argc, char **argv)   
{   
    char       buffer[BUFSIZ];   
    size_t     osize, nsize;   
    FILE       *str;   
    const char *filename;   
    int        count;   
   
    //setlocale(LC_ALL, "");   
    //bindtextdomain(PACKAGE, LOCALEDIR);   
    //textdomain(PACKAGE);   
   
    if (argc != 2) {   
    fprintf(stderr, _("Usage: tailf logfile\n"));   
    exit(1);   
    }   
   
    filename = argv[1];   
   
    tailf(filename, 10);   
   
    for (osize = filesize(filename);;) {   
    nsize = filesize(filename);   
    if (nsize != osize) {   
        if (!(str = fopen(filename, "r"))) {   
        fprintf(stderr, _("Cannot open \"%s\" for read\n"), filename);   
        perror(argv[0]);   
        exit(1);   
        }   
        if (!fseek(str, osize, SEEK_SET))   
                while ((count = fread(buffer, 1, sizeof(buffer), str)) > 0)   
                    fwrite(buffer, 1, count, stdout);   
        fflush(stdout);   
        fclose(str);   
        osize = nsize;   
    }   
    usleep(250000);     /* 250mS */   
    }   
    return 0;   
}   
   

gcc -Wall -o /usr/bin/tailf tailf.c