while (my $line = <INFILE>) {
    if ( ($. % 5000) == 0) {
        print "Processed $. records\n";
        # or, just to let them know
        # print ".";
    }
    ## process away
}

##</code><code>##

my $TOTAL = (-s $FILE);
while (read(INFILE,$buf,$bufsize)) {
    ## do work
    $BYTES_READ+=$bufsize;
    if ( ($BYTES_READ % 5000) == 0) {
        printf("%.3f %% (%d of %d)\n",($BYTES_READ/$TOTAL)*100,$BYTES_READ,$TOTAL);
    }
}