text-utils/tailf.c

   1 /* tailf.c -- tail a log file and then follow it
   2  * Created: Tue Jan  9 15:49:21 1996 by faith@acm.org
   3  * Copyright 1996, 2003 Rickard E. Faith (faith@acm.org)
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining a
   6  * copy of this software and associated documentation files (the "Software"),
   7  * to deal in the Software without restriction, including without limitation
   8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   9  * and/or sell copies of the Software, and to permit persons to whom the
  10  * Software is furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be included
  13  * in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  19  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  20  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  21  * OTHER DEALINGS IN THE SOFTWARE.
  22  *
  23  * less -F and tail -f cause a disk access every five seconds.  This
  24  * program avoids this problem by waiting for the file size to change.
  25  * Hence, the file is not accessed, and the access time does not need to be
  26  * flushed back to disk.  This is sort of a "stealth" tail.
  27  */
  28
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <unistd.h>
  32 #include <malloc.h>
  33 #include <sys/stat.h>
  34 #include "nls.h"
  35
  36 static size_t filesize(const char *filename)
  37 {
  38     struct stat sb;
  39
  40     if (!stat(filename, &sb)) return sb.st_size;
  41     return 0;
  42 }
  43
  44 static void tailf(const char *filename, int lines)
  45 {
  46     char **buffer;
  47     int  head = 0;
  48     int  tail = 0;
  49     FILE *str;
  50     int  i;
  51
  52     if (!(str = fopen(filename, "r"))) {
  53         fprintf(stderr, _("Cannot open \"%s\" for read\n"), filename);
  54         perror("");
  55         exit(1);
  56     }
  57
  58     buffer = malloc(lines * sizeof(*buffer));
  59     for (i = 0; i < lines; i++) buffer[i] = malloc(BUFSIZ + 1);
  60
  61     while (fgets(buffer[tail], BUFSIZ, str)) {
  62         if (++tail >= lines) {
  63             tail = 0;
  64             head = 1;
  65         }
  66     }
  67
  68     if (head) {
  69         for (i = tail; i < lines; i++) fputs(buffer[i], stdout);
  70         for (i = 0; i < tail; i++)     fputs(buffer[i], stdout);
  71     } else {
  72         for (i = head; i < tail; i++)  fputs(buffer[i], stdout);
  73     }
  74     fflush(stdout);
  75
  76     for (i = 0; i < lines; i++) free(buffer[i]);
  77     free(buffer);
  78 }
  79
  80 int main(int argc, char **argv)
  81 {
  82     char       buffer[BUFSIZ];
  83     size_t     osize, nsize;
  84     FILE       *str;
  85     const char *filename;
  86     int        count;
  87
  88     setlocale(LC_ALL, "");
  89     bindtextdomain(PACKAGE, LOCALEDIR);
  90     textdomain(PACKAGE);
  91
  92     if (argc != 2) {
  93         fprintf(stderr, _("Usage: tailf logfile\n"));
  94         exit(1);
  95     }
  96
  97     filename = argv[1];
  98
  99     tailf(filename, 10);
 100
 101     for (osize = filesize(filename);;) {
 102         nsize = filesize(filename);
 103         if (nsize != osize) {
 104             if (!(str = fopen(filename, "r"))) {
 105                 fprintf(stderr, _("Cannot open \"%s\" for read\n"), filename);
 106                 perror(argv[0]);
 107                 exit(1);
 108             }
 109             if (!fseek(str, osize, SEEK_SET))
 110                 while ((count = fread(buffer, 1, sizeof(buffer), str)) > 0)
 111                     fwrite(buffer, 1, count, stdout);
 112             fflush(stdout);
 113             fclose(str);
 114             osize = nsize;
 115         }
 116         usleep(250000);         /* 250mS */
 117     }
 118     return 0;
 119 }