I'm sorry. I asked a similar question before but lost track of it as I went out of town for a few days. The original question was to parse a custom filter and apply to a dataset. For example, parse this filter: 
(AND
      (OR
            AUTHOR=John PROFIT=90%
            AUTHOR=Matt PROFIT=80%
      )
      PUBLISHER=OReilly
)

[download]
And apply to: 
Page 1

AUTHOR: John
PROFIT: 20%
PUBLISHER: TMH
BOOK: OPERATING SYSTEMS

Page 2

AUTHOR: John
PROFIT: 90%
PUBLISHER: OREILLY
BOOK: ALGORITHMS

Page 3

AUTHOR: Matt
PROFIT: 80%
PUBLISHER: TMH
BOOK: COMPUTER NETWORKS

Page 4

AUTHOR: Matt
PROFIT: 80%
PUBLISHER: OREILLY
BOOK: COMMUNICATION SYSTEMS

[download]
to get the relevant results. I think it was BrowserUK who gave me a working solution which was this: 
#! perl -slw
use strict;

## Convert query syntax to evalable Perl code
sub buildQuery {
    local $_ = uc shift;
    while( m[ \( (?: AND | OR ) | != | = ]x ) {

        s< ( [^!=()\s]+ ) ( != | = ) ( [^()\s]+ ) >{
            my $op = ( $2 eq '!=' ? 'ne' : 'eq' );
            "[\$\L$1\E $op '$3']";
        }xge;

        s< \( \s* ( AND ) \s+ ( \[ [^()]+ \] ) \s+ ( \[ [^()]+ \] ) \s
+* \) >
        { "[$2 && $3]" }xge;

        s< \( \s* ( OR ) \s+ ( \[ [^()]+ \] ) \s+ ( \[ [^()]+ \] ) \s*
+ \) >
        { "[$2 || $3]" }xge;
    }
    tr/[]/()/;
    return $_;
}

## Read data and UPPER case
my $data = do{ local $/; uc <DATA> };

## Some variables
my( $author, $profit, $publisher, $book );

## And a regex to populate them from each record
my $re = qr[
    PAGE        \s+ \d+ \s+
    AUTHOR:     \s+ ( [^\n]+ ) (?{ $author    = $^N }) \s+
    PROFIT:     \s+ ( [^\n]+ ) (?{ $profit    = $^N }) \s+
    PUBLISHER:  \s+ ( [^\n]+ ) (?{ $publisher = $^N }) \s+
    BOOK:       \s+ ( [^\n]+ ) (?{ $book      = $^N }) \s+
]x;

## Covert the query NOTE: (AND ) syntax is required
## where example used implicit AND
my $query = buildQuery( <<EOQ );
(AND
    (OR
        (AND AUTHOR=John PROFIT=90% )
        (AND AUTHOR=Matt PROFIT=80% )
    )
    PUBLISHER=OReilly
)
EOQ
print "\nQuery: $query\n";

## Test the condition and print the record if it matches
## For each record
eval "$query" and print $1 while $data =~ m[ ( $re ) ]xg;

## Same again for another query
## Note != also accepted.
my $query2 = buildQuery( <<EOQ );
(OR
    (AND AUTHOR=John PROFIT!=90% )
    (AND AUTHOR=Matt PUBLISHER!=OReilly )
)
EOQ
print "\nQuery: $query2\n";

eval "$query2" and print $1 while $data =~ m[ ( $re ) ]xg;


__DATA__
Page 1

AUTHOR: John
PROFIT: 20%
PUBLISHER: TMH
BOOK: OPERATING SYSTEMS

Page 2

AUTHOR: John
PROFIT: 90%
PUBLISHER: OREILLY
BOOK: ALGORITHMS

Page 3

AUTHOR: Matt
PROFIT: 80%
PUBLISHER: TMH
BOOK: COMPUTER NETWORKS

Page 4

AUTHOR: Matt
PROFIT: 80%
PUBLISHER: OREILLY
BOOK: COMMUNICATION SYSTEMS

[download]
Now, the problem is I have to use the same filter in a code that I've already written for another format. I have some lines in my code that print the fields: 
        print $db_title."\n";
    print $db_source."\n";
    print $db_length."\n";
    print $db_author."\n";
    print $db_body."\n";
    print $db_language."\n";
    print $db_subject."\n";
    print $db_datepub."\n";
    print $db_loaddate."\n";
    print "\n\n\n";

[download]
Now, I have to print all the fields only if the filter condition matches but I am unable to get it right on how to use the filter with this data. Can someone help me out please?

In reply to Filtering some text by legend

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