Perhaps overkill for this application, but useful where the gathering of a predetermined set of fields is spread over a more complex gathering process.

1. Predefine the hask keys, setting the values to undef.
2. Use Internals::SetReadOnly to ensure that no other spurious keys can be autovivified accidentally.
3. Use (Updated)keys( %hash ) == grep defined, values( %hash ) to ensure that you got them all.

   Or more simply, 0 == grep !defined, values %hash;

use Internals qw[ SetReadOnly ];

my %hash; 
undef @hash{ qw[ the quick brown fox ] };
SetReadOnly( \%hash );
...

while( <$fh> ) {
    if( ... some capturing regex ... ) { 
        $hash{ $1 } = $2;
    }
    elsif( ... regex ... ) {
        $hash{ $1 } = $2;
    }
    else {
        $hash{ fox } == FOX_DEFAULT;
    }
    last if keys %hash == grep defined, values( %hash ); ## Updated, s
+ee below.
}
[download]

In the event that one of your regex accidentally matches the wrong key/value pairing, setting (say) $1 = 'bill', then you'll get a fatal error:

Attempt to access disallowed key 'bill' in a restricted hash at yoursc
+ript.pl line nn, <$fh> line mm
[download]

Telling you not only which line of code the error occured, but also which line of the data file (and the value) that was involved.