It would be use Module1 || use Module2, but that doesn't work because use dies on failure. You might try to wrap the use in an eval BLOCK, but that doesn't work because of compile-time vs run-time issues. You could succeed, however, by following the advice given in "use" dynamic module. Alternativly, eval EXPR does the trick:

# Approximate
#    use Module1 || use Module2;

BEGIN {
   eval qq{ use Module1 };
   eval qq{ use Module2 } if not $@;
   die("Unable to load Module1 or Module2\n" if not $@;
}
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