I must be missing something here...

You're slurping it line-by-line with <$tail>, and emailing the lines containing the error. What are you resetting file position for? The loop will just proceed to the next line automatically. Why close and reopen? I guess the log is being rotated underneath?

For this sort of thing I'd probably read from a 'tail -F' pipe instead and keep the perl part trivial. Or use any of the multitude of CPAN tail modules, rather than trying to reimplement tail all over again.

See logtail2(and its manpage), which save an offset and allow you to read the file only from the last line which was read.

You can modify it to get your goal, or pipe it to a simple perl script

dirtdog:

Like armstd mentioned, part of the problem is that you're rewinding the file to the beginning. I'd suggest tracking the last line of the file you examined each time with a log tailing module (as described to by i5513) or something like this (untested):

sub saveFilePos {
    my ($fileno, $filename) = @_;
    my $filepos = tell($fileno);
    open my $FH, '>', $filename or die "Can't open $fname: $!";
    print $FH $filepos;
    close $FH;
}

sub process {
    my $file = "/$ENV{HOME}/Error.log";
    my $file_last = "/$ENV{HOME}/Error.log.lastpos";
    my $file_pos = 0;   # Default to beginning of file
    eval {
        # Get last position in file (if any)
        open my $FH, '<', $file_last;
        if ($FH) {
            $file_pos = <$FH>;
            close $FH;
        }

        open ($tail,"<",$file_name) or die "Can't open file $file_name
+";
        seek($tail, $file_pos, 0);
        for(;;) {
            for $line (<$tail>) {
                if ( /OutOfMemoryError/) {
                    send_mail($_,$.);
                }
            }
        }

        # Save last position examined
        saveFilePos($tail, $file_last);
        close($tail);
    }
}
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When your only tool is a hammer, all problems look like your thumb.