Re: reading from a file

[Octavian Rasnita]

Thank you. The program works and it prints the lines from the file, but it 
also waits for more seconds before printing a new group of last added lines.

I think it is a problem due to the program that makes the link between the 2 
computers. I don't remember its name, but it is not Samba.

Thanks.

Octavian

----- Original Message ----- 
From: "Andrew Curry" <[EMAIL PROTECTED]>
To: "Octavian Rasnita" <[EMAIL PROTECTED]>; "Jeff Pang" 
<[EMAIL PROTECTED]>; "beginners perl" <beginners@perl.org>
Sent: Tuesday, July 24, 2007 1:12 PM
Subject: RE: reading from a file


If you want an over complex solution you could try using

use IPC::Open3;
use IO::Select;
use IO::Handle;

i.e.

#!/usr/local/bin/perl -w
use Data::Dumper;
use File::Copy;
use IPC::Open3;
use IO::Select;
use IO::Handle;
use strict;

use vars qw(
 $line $select
 $read $write $error
);

( $select, $read, $error ) =
 process_command('/usr/bin/tail -f tmp.dat');
 process_tail($select);
close_handles( $read, $error );

sub process_command {
   my ($command) = @_;

   my ( $pid, $readbuff, $timeout, $s );
   $timeout = 10;
   $read    = new IO::Handle;
   $error   = new IO::Handle;

   $pid = open3( $write, $read, $error, $command );

   #
   # create selects
   #
   $s = IO::Select->new();
   $s->add($read);
   $s->add($error);

   return ( $s, $read, $error ); }

sub process_tail {
   my ($select) = shift;
   my ( @ready, $handle, $timeout, $readbuff, $flag, $tapeloc, $newnum );
   $flag = 0;

   #
   # get write handle
   #

   while ( $flag == 0 ) {
       @ready = $select->can_read($timeout);

       foreach $handle (@ready) {
           sysread( $handle, $readbuff, 256 ); # 256 is the number of 
chars
to read.

           if ( length($readbuff) == 0 ) {
               $flag = 1;
           }
       }
#
# do something here
#
print "$readbuff\n";
       }
       sleep(1);
   }

sub close_handles {
   my ( $r, $e ) = @_;
   $r->close();
   $e->close();
}


Its not been tested so not sure if it will do what you require.

-----Original Message-----
From: Octavian Rasnita [mailto:[EMAIL PROTECTED]
Sent: 24 July 2007 10:45
To: Jeff Pang; beginners perl
Subject: Re: reading from a file

From: "Jeff Pang" <[EMAIL PROTECTED]>


--- Octavian Rasnita <[EMAIL PROTECTED]> wrote:

Hi,

I am trying to read from a log file which increase continuously
almost every second.

You may try the Unix 'tail' command and pipe the result to your Perl
program.Like:

tail -f access_log|perl -e
'while(<>){handle_routine()}'

handle_routine() is your routine for handling logfile lines.



I can do this, but in that case I don't know how to be sure that I don't
skip any line of the file.
The condition is to not skip any line and to not get the same line twice.

I tested the tail command in the command line using:

tail -n 1 /path/to/file

because I wanted to get only the last line of the file.

If I use that command for more times, sometimes the same last line is
printed for more times, but sometimes the tail command doesn't print
anything.

I don't know if the result of tail can be trusted...

Thank you.

Octavian



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