Here's a good way if you want to fetch multiple values from the hash: (you mentioned slice)

my $result = {
   'TEST[2]'     => '24',
   'RESPMSG[30]' => 'invalid or empty account expir',
};

my %lookup;
$lookup{/^(.*)\[\d+\]$/ ? $1 : $_} = $_ foreach (keys(%$result));

print($result->{$lookup{'TEST'}}, $/);
# 24

my @slice = @$result{$lookup{'TEST'}, $lookup{'RESPMSG'}};
print(join(', ', @slice), $/);
# 24, invalid or empty account expir

my @keys = ('TEST', 'RESPMSG');
my %subhash = map { shift(@keys) => $_ } @$result{@lookup{@keys}};
print(join(', ', %subhash), $/);
# TEST, 24, RESPMSG, invalid or empty account expir

my @keys2 = ($lookup{'TEST'}, $lookup{'RESPMSG'});
my %subhash2 = map { shift(@keys2) => $_ } @$result{@keys2};
print(join(', ', %subhash2), $/);
# TEST[2], 24, RESPMSG[30], invalid or empty account expir
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