And what about another program that only has one executable file?

my $binary = "/path/to/executable";
-x $binary or die "$binary not found";
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FM seems to be under Windows, since he asks about Win32::DirSize. But I guess -x is *NIX-centric and I don't know how it would behave under redmondish environments. Maybe it would just evaporate silently to -f, but I would probably use directly the latter:

-f or die "`$_' binary not found\n" for 'C:/path/to/executable';
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