my %results;
for my $tok ( split /\s+/, $input ) {
  $results{ $1 } = $2 if $tok =~ /^ (.) = (\d+) $/x;
}

for my $k ( qw( a b c ) ) {
  print "$k is ", exists $results{ $k } ? $results{ $k } : 'missing', "\n";
}