This gives you your desired output: 
use warnings;
use strict;

my %results = (a => 1);

foreach my $var (keys %results) {
    while (my $attr_line = <DATA>) {
        if ($attr_line =~ /^\Q$var/ ) {
            print $attr_line;
        }
    }
}

__DATA__
a|12
a[11]|1
a[11][11]|0
b|2
c|0

[download]
Update: in response to to OP's update, read http://sscce.org

In reply to Re: Parsing for [] in a file by toolic
in thread Parsing for [] in a file by HJ

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