# 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]

Sometimes being able to do it in "just a few lines" isn't the point (take Data::Page for example). It's having to always rewrite, correctly, those lines every time you want to solve this particular problem. In this case, the module makes for a more flexible solution, and it's a "few lines" (about 12 actually) that I don't have to rewrite. The downside is that it is about 20% slower, but that's a non-issue when response to any single query is imperceptible.

I can't see much justification for anything more complicated.


Optionally searching for strings instead of numbers?
Not having to have a fixed record size or not having to know what the recordsize is? (note: there is a set recordsize function in File::SortedSeek which claims to improve performance, but I could not see any difference in speed from using it)

Anyway, here's your function using F:SS instead:

use File::SortedSeek;

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

    # I don't see any difference in speed with the next line
    # File::SortedSeek::set_line_length($recordsize);
    numeric( $fh, $key);
    return File::SortedSeek::was_exact();
}
[download]

Update: Looking at the answers below, I learned about Search::Dict, which would work just about as well, and has been in core perl since at least 5.6.1, but still supports my point about saving just a few lines.