Wise brothers, I seek your wisdom.

I am looking to monitor changes to a log file that has a Unicode (utf-16) encoding. The file is a log from a windows application, where the application will from time wake up, truncate the file and start emitting log messages to the file. When it finishes a job it will add a 'job done' message to the log and then go back to sleep. I would like to know when those job done messages are written so I can trigger other events.

My initial plan was to use File::Tail to monitor the file:

my $o_tail=File::Tail->new( 
    name               =>  $scan_log_file, 
    maxinterval        =>  1, 
    adjustafter        =>  1, 
    ignore_nonexistant =>  1, 
    reset_tail         => -1,
    tail               => -1,
);

while( my $line = $o_tail->read() )
{
    if( $line =~ m/finished/ )
    {
        # Do stuff
    }
}

[download]

The problem with this is that the file is utf-16, and the lines I get back are encoded rather than perl strings.

From the File::Tail docs, there is no way to provide an encoding as a parameter, and looking at the source it look like that module makes a lot of sysseek and sysread calls, that I guess would not work properly via a Unicode input layer. (Because the one to one relationship between characters and bytes would no longer hold true), so I think patching File::Tail to support Unicode would be a difficult undertaking.

Another approach I thought of is to accept the octet strings from File::Tail, and then pass them through $string = decode("utf-16", $octets) (From the Encode) module. A possible problem with this approach is how newlines are encoded, and how File::Tail copes with them.

A third approach would be to abandon the use of File::Tail, and instead to stat() the file at frequent intervals, and every time it changes, read the entire file using standard IO with a suitable encoding.

Do you have any thoughts or suggestions?

In reply to Using File::Tail on a unicode file by chrestomanci

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