I don't think using /^$key/ is a good idea because you want an exact match so that a key of "b" doesn't find an entry of "bbking" => "legend". A test for string equality would be safer.

use strict;
use warnings;

my @ta = (q{a x}, q{b y}, q{c z});

my $key = q{b};
print qq{key = $key, value is @{[getValue($key)]}\n};

sub getValue
{
    my $key = shift;
    return
       map  { $_->[1] }
       grep { $_->[0] eq $key }
       map  { [ split ] }
       @ta;
}
[download]

The output is

key = b, value is y
[download]

I hope this is of use.

Cheers,

JohnGG

Update: Thinking about it, you could do most of the work inside the print statement, getting rid of the subroutine

use strict;
use warnings;

my @ta = (q{a x}, q{b y}, q{c z});

my $key = q{b};
print qq{key = $key, value is @{ [ 
   map  { $_->[1] }
   grep { $_->[0] eq $key }
   map  { [ split ] }
   @ta ] }\n};
[download]

This produces the same output as the first version.