If a module returns false, then its filename is not added to %INC, which is supposed to mean that the module hasn't been loaded. But if it never returns anything, i.e. if there's a compile-time error or the module throws an exception, then the filename is added to %INC. As a result, if you try to load a module twice in a row, it can fail the first time and then look like it succeeds the second time, even though the file still doesn't really load successfully. Example: 
foo.pl:

  for (1..2) {
    eval "require bar";
    print "attempt $_: ", ($@ ? 'fail' : 'succeed'), "\n";
  }

bar.pm:

  die;

> perl foo.pl
attempt 1: fail
attempt 2: succeed

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Is this a perl bug, or is there some justification for the behavior? What's the correct way to load a module if and only if it hasn't already been loaded successfully?

In reply to Failed require looks like it succeeded by Anonymous Monk

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