The answer to the literal question in your title is: if you need to ask, you shouldn't be using perl. ^* Taking into account the example in your post, you should probably use an array or hash lookup instead if you have a large (for some value of large) amount of tests:

my @lookup = (
  sub { 
     # condition 0
  },
  sub { 
     # condition 1
  },
  sub { 
     # condition 2
  },
  ... 
);
$lookup[$condition]->();
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*) update: what I meant is; if the speed difference is relevant to your application you should be using a faster language - C for example.