Tie::File will serve you well here.

use Tie::File ;

my $data_file="learn.data";
my $search_for = 'foo' ;

tie my @raw_data, 'Tie::File', $data_file or die ;
for ( my $row = 0 ; $row < $#raw_data; ++$row ) {
    if ( $raw_data[ $row ] =~ /$search_for/ ) {
        my $matching_row  = $raw_data[ $row ] ;
        my $previous_row  = $raw_data[ $row - 1 ] ;
        my $following_row = $raw_data[ $row + 1 ] ;
        ### And so on and so forth...
    }
}
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Those who know that they are profound strive for clarity. Those who
would like to seem profound to the crowd strive for obscurity.
            --Friedrich Nietzsche