AW: reading from a file

[Angerstein]

There is a modul on cpan that does what you want.
It´s called File::Tail or something like that.

-----Ursprüngliche Nachricht-----
Von: Andrew Curry [mailto:[EMAIL PROTECTED] 
Gesendet: Dienstag, 24. Juli 2007 12:12
An: Octavian Rasnita; Jeff Pang; beginners perl
Betreff: 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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