wishartz has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, I wonder if anybody can help me. I would like to use the POE::FollowTail module to follow various system log files, like /var/log/messages and /var/log/secure and then report any new messages to the user. I have the following example from the POE website, but what I would like it to do, is every time a new message appears to bring up a new xterm console window with the new message being displayed. Using the following code, how can I make it display the messages in a new xterm window, for each different log file. Thanks. 
#!/usr/bin/perl -w

# http://poe.perl.org/?POE_Cookbook/Watching_Logs

use POE qw/Wheel::FollowTail/;
use strict;

$| = 1;

my $filename = $ARGV[0];

die "Usage: $0 <filename>\n"                     unless $filename;
die "$0: $filename: No such file or directory\n" unless -e $filename;
die "$0: $filename: Permission denied\n"         unless -r $filename;

POE::Session->create
  ( inline_states =>
      { _start => sub { $_[HEAP]->{wheel} =
              POE::Wheel::FollowTail->new(
                Filename   => $_[ARG0],
                InputEvent => 'got_line',
                ErrorEvent => 'got_error',
                SeekBack   => 1024,
              );
            $_[HEAP]->{first} = 0;
        },
        got_line => sub { print "$_[ARG0]\n" if $_[HEAP]->{first}++ },
        got_error => sub { warn "$_[ARG0]\n" },
      },
    args => [$filename],
  );

$poe_kernel->run();

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Replies are listed 'Best First'.
Re: POE::FollowTail and xterm
by moklevat (Priest) on Apr 16, 2008 at 15:30 UTC
    If I understand correctly, you would like to use this followtail script to monitor several log files, and you would like to launch a separate xterm for each separate log file. This is fairly straightforward and you could simply shell script the launching of the followtail script 
    #!/bin/bash
 xterm -hold -e /path/to/follow-tail.pl /var/log/httpd/access_log > /d
+ev/null &
 xterm -hold -e /path/to/follow-tail.pl /var/log/httpd/error_log > /de
+v/null &

    [download]
    Is this what you had in mind? I thought briefly that you might want a separate xterm for each message, but that could generate thousands of xterms very quickly, and thus would be silly (to use the technical term).
[reply]
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Re: POE::FollowTail and xterm
by elmex (Friar) on Apr 16, 2008 at 15:25 UTC

    Hmm, I guess the problem is to start an xterm and actually delivering the message there. I would probably start the X term with another script that would connect the my log-analyzing process via a unix socket or some other form of IPC and receive the message from there.

    But I didn't really understand your problem: Do you want a new xterm for every log-message or only one xterm per logfile?

    If you want one xterm per logfile the best would probably just to startup the xterms and run a tail there.

[reply]
Re: POE::FollowTail and xterm
by glide (Pilgrim) on Apr 16, 2008 at 22:19 UTC
[reply]
      Thanks for your help. I wasn't absolutely clear on what I wanted to do. The problem is this program will be for some operators at work and they will be informed when there is a new message for them to take note of. The old script that we use at work was written in kornshell and is run by a crontab every two minutes. What it does is, make a copy of the log file and then compare another version of the log file two minutes later and report if there are any new messages and bring them up in a new xterm window. There is a new xterm window for each log file every two minutes. The reason, I am changing the script is it is not ideal, it's a bit of an overhead to compare the files every two mins. With POE::followtail I don't need to run a cron I could just keep it running and informing on new messages. I could also choose to exclude certain messages as well. I didn't really want to run two scripts to redirect the output to an xterm window, is there anyway of redirecting the output to a new xterm console in the perl script? Thanks
[reply]
        Using the following code, is there any way that I can make it open a new xterm for each log file? 
        
my %logs_to_watch =
  ( cron => "/var/log/cron",
    mail  => "/var/log/maillog",
    ppp   => "/var/log/ppp.log",
    httpd => "/var/log/httpd-access.log",
    msg   => "/var/log/messages",
  );

# Start a session to watch the logs.

POE::Session->create
  ( inline_states =>
      { _start => \&begin_watchers,

        # Handle records from each log differently.
        cron_record  => \&cron_got_record,
        mail_record  => \&mail_got_record,
        ppp_record   => \&ppp_got_record,
        httpd_record => \&httpd_got_record,
        msg_record   => \&msg_got_record,

        # Handle log resets and errors the same way for each file.
        log_reset => \&generic_log_reset,
        log_error => \&generic_log_error,
      }
  );


=for cookbook

Start log watchers.  Scans the hash of %logs_to_watch, creating a new
FollowTail wheel to watch each.

Each watcher emits an event based on its key in %logs_to_watch.  Those
events are handled by functions that will parse, filter, and if
necessary display information about the records.

For example, cron is the key for "/var/log/cron".  The cron log
watcher will emit a "cron_record" event whenever that file extends.
The POE::Session->create() call above associates the "cron_record"
event with the cron_got_record() function later on.

=cut

sub begin_watchers {
    my $heap = $_[HEAP];

    while ( my ( $service, $log_file ) = each %logs_to_watch ) {
        my $log_watcher = POE::Wheel::FollowTail->new
          ( Filename => $log_file,
            InputEvent => $service . "_record",
            ResetEvent => "log_reset",
            ErrorEvent => "log_error",
          );

        $heap->{services}->{ $log_watcher->ID } = $service;
        $heap->{watchers}->{ $log_watcher->ID } = $log_watcher;
    }
}

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