You do have code for these cases? So in addition to your logic above you have:

sub this {
  return "this"; # Whatever
}

sub that {
  return "that"; # Being simple here
}
# etc
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Combine the two:

my %action = (
  this => sub {return "this"},
  that => sub {return "that"},
  # etc
);

# Then later:
if (exists $action{$in}) {
  $action{in}->();
}
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In fact if you have a lot of cases you can probably find room to factor:

sub ret_simple_returner {
  my $arg = shift;
  return ($arg, sub {$arg});
}

my %action = map ret_simple_returner($_), qw(this that);
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The point being that every time you eliminate the need to keep two pieces of code in sync you eliminate another possible source of bugs...