I think you want to replace:

eval "use $perl_module" or die "Can't find $perl_module: $!\n";
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by:

eval "use $perl_module"; 
die "Can't find $perl_module: $@\n" if $@;
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Eval just returns whatever was returned by use, which to my knowledge is undefined (please someone correct me if I'm wrong).

You need to check whether $@ is non-empty after the eval().

Liz