eval "use Some::Module 94.5";
 
if($@) {
  print "Oh noes, it's not installed!\n";
} else {
  ...
}
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Checking $@ is not an appropriate way to check if an eval failed. An eval can fail, but in the clean up (DESTROY for instance), something can unset $@.

The only way to make sure an eval succeeded is to check its return value:

eval "use Some::Module 94.5; 1" or do {
    printf "Loading Some::Module failed: %s", $@ // "Unknown error";
    ...
};
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Can you give an example that would make my code Do The Wrong Thing? Cos I can't think of any way of doing that.