Seems almost like overkill when it can be done in just a few lines. The function below searches three million records very quickly. 
# Usage: record_search($search_string, $filename, 11);
# Returns the record number if the record is found, undef otherwise.
# Searched file must be sorted.

sub record_search {
    my ($key, $filename, $recordsize) = @_;
    my $fh = IO::File->new($filename, 'r')
        or croak("Could not open `$filename': $!");

    my $hi = ($fh->stat)[7] / $recordsize;
    my $lo = 0;

    while ($lo < $hi) {
        my $mid = int(($lo + $hi) / 2);
        $fh->seek($mid * $recordsize, 0);
        my $target = $fh->getline();
        chomp($target);

        if ($target < $key) {
            $lo = $mid + 1;
        } elsif ($target == $key) {
            return $mid;
        } else {
            $hi = $mid;
        }
    }
}

[download]
Update Forgot to mention: even though this function opens the file every time, it can successfully search 3 million records about 2000 times per second on a 3Ghz Pentium 4. I can't see much justification for anything more complicated. Threads? Bit strings? Crazy! :)

In reply to Re^3: Searching text files by xach
in thread Searching text files by SteveS832001

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