my @date = grep /$date/,@{$countries${cntry_of_issue}})
That code doesn't even compile. Try this instead: 
my @dates = grep /$date/, @{ $countries{$cntry_of_issue} };

[download]

I got rid of the unmatched right paren, added a semicolon, and moved the dollar sign to the right of the curly bracket to form the scalar variable $cntry_of_issue, rather than the bareword cntry_of_issue.

Here is a self-contained example which seems to work for me: 

use warnings;
use strict;
use Data::Dumper;

my %countries;
while (<DATA>) {
        chomp;
        next if /^\s*$/ || /^\#/;
        my $aref = [split /,/, $_];
        push( @{$countries{$aref->[2]}}, $aref->[5]);
}

my $date = 20100101;
my $cntry_of_issue = 'CH';
my @dates = grep /$date/, @{ $countries{$cntry_of_issue} };
print Dumper(\@dates);

__DATA__
978,XBRN,CH,Berne Stock Exchange,2010,20100101
978,XBRN,CH,Berne Stock Exchange,2010,20100102
978,XBRN,CH,Berne Stock Exchange,2010,20100321
978,XBRN,CH,Berne Stock Exchange,2010,20100324

[download]
Prints: 
$VAR1 = [
          '20100101'
        ];

[download]

In reply to Re: Trouble grepping values when hash contains multiple values per key by toolic
in thread Trouble grepping values when hash contains multiple values per key by dirtdog

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