my %values = (
    a => 'value a',
    b => 'value b',
    c => 'value c',
    d => 'value d',
);

if( $str=~       m/(\S)\s(\S)\s(\S)\s(\S)/) {
    my @captured = ($1,   $2,   $3,   $4);
    ($a,$b,$c,$d)= map { $values{ $_ } || $_ } @captured;
};
print $a,"\n",$b,"\n",$c,"\n",$d;