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/* tailf.c -- tail a log file and then follow it
* Created: Tue Jan 9 15:49:21 1996 by r.faith@ieee.org
* Revised: Thu Jan 11 16:47:20 1996 by r.faith@ieee.org
* Copyright 1996 Rickard E. Faith (r.faith@ieee.org)
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2, or (at your option) any
* later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 675 Mass Ave, Cambridge, MA 02139, USA.
*
* $Id: tailf.c,v 1.1 1996/01/11 21:51:07 faith Exp $
*
* 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 <unistd.h>
#include <malloc.h>
#include <sys/stat.h>
size_t filesize( const char *filename )
{
struct stat sb;
if (!stat( filename, &sb )) return sb.st_size;
return 0;
}
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( char * ) );
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;
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 );
}
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;
}
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