Print preceding line from text database

nasa has asked for the wisdom of the Perl Monks concerning the following question:

I have pulled a line out of a database thus.

$data_file="learn.data";
open(DAT, $data_file) || die("Could not open file!");
@raw_data=<DAT>;
@results = grep( /^$line[0]/, @raw_data );
foreach( @results ) {
    $record = $_;   
}
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Then I have split the line thus.

open(I, $data_path);
$found=0;
 while(<I>){
    chomp;
    @line = split(/\t/, $_);
    if($line[0] eq $GET{'id'}){
        $found=1;
        last;
    }
}
close(I);
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Puzzle is. How can I ask, What is the preceding line in the database.? Give me the line that was printed just before the one we just extracted.? May god bless your living sole . Nasa.

update (broquaint): title change (was What wize monk can help?)

Comment on Print preceding line from text database Select or Download Code

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Re: What wize monk can help? by DamnDirtyApe (Curate) on Nov 27, 2002 at 22:00 UTC
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[ $row + 1 ] ; ### And so on and so forth... } }` [download] _______________ DamnDirtyApe Those who know that they are profound strive for clarity. Those who would like to seem profound to the crowd strive for obscurity. --Friedrich Nietzsche	[reply] [d/l]
Re: What wize monk can help? by John M. Dlugosz (Monsignor) on Nov 28, 2002 at 00:45 UTC
At the end of the while loop's body, say `$prev_line= $_;` to save what you have before doing `<I>` again. I'd also go ahead and used a named variable instead of relying on $_ to still hold the line. Something like: `my ($current_line, $prev_line); while($current_line=<I>){ chomp; @line = split(/\t/, $_); if($line[0] eq $GET{'id'}){ $found=1; last; } $prev_line= $current_line; } close(I); # value in $prev_line still good.` [download]	[reply] [d/l] [select]