The "Found = in Conditional" warning was not from the tertiary, but the logical and. Since you are not really doing a logical test, but just combining statements, I would use the comma operator, here.

$allowed{action} = 'post|edit|delete|long|short';
$query->{action} eq "post"
  ? (($allowed{msgid} = '^(\d+|new)$'),
    ($allowed{data}  = '^(([^|+]*[^|]+.*\|){4}[^|+]*[^|]+.*)$'))
  : 1;
$query->{action} eq "edit"
  ? ($allowed{msgid} = '^(\d+|new)$')
  : 1;
$query->{action} eq "delete"
  ? ($allowed{msgid} = '^(\d+)$')
  : 1;
$query->{action} eq "long"
  ? (($allowed{sort}  = '^(author|date|subject|expire)$'),
    ($allowed{msgid} = '^(\d*|all)$'))
  : 1;
$query->{action} eq "short"
  ? (($allowed{sort}  = '^(author|date|subject|expire)$'),
    ($allowed{msgid} = '^(\d+|all)$'))
  : 1;

foreach $key (keys %$query){
  exists $allowed{$key} ? 1 : return 0;
  return 0 if $query->{$key}!~/$allowed{$key}/;
  1;
}
[download]

Now, that said, here's another way to handle this:

# Map keys to coderefs (used sort of like a switch statement)
my %ActionMap =
  (post => sub{
     $allowed{msgid} = '^(\d+|new)$';
     $allowed{data}  = '^(([^|+]*[^|]+.*\|){4}[^|+]*[^|]+.*)$';
   },
   edit => sub{
     $allowed{msgid} = '^(\d+|new)$';
   },
   delete => sub{
     $allowed{msgid} = '^(\d+)$';
   },
   long => sub{
     $allowed{sort}  = '^(author|date|subject|expire)$';
     $allowed{msgid} = '^(\d*|all)$';
   },
   short => sub{
     $allowed{sort}  = '^(author|date|subject|expire)$';
     $allowed{msgid} = '^(\d+|all)$';
   });
# "Call" the coderef matching the "switch" value
$ActionMap{$query->{action}}->();

for my $key (keys %$query){
  return 0 unless exists $allowed{$key} && $query->{$key} =~ /$allowed
+{$key}/;
}
[download]

Notes:

• I'm concerned about the for loop. It looks like $query->{$key} will never match /$allowed{$key}/. This was just a code example, though, so...
• This "switch" construct avoids your void-context values. The ternary may feel easier to read, but it leaves the reader wondering what you are doing with that 1 in each ternary.
• There are, of course, other ways to do "switch" statements...this is merely one of them.

Russ
Brainbench 'Most Valuable Professional' for Perl