my $code = system(q{apt-get -qq -o 'Debug::NoLocking=true' --simulate upgrade});
print "code: ";
print ($code & 127);
print ";\n";

##</code><code>##

code: 0;

##</code><code>##

$ apt-get -qq -o 'Debug::NoLocking=true' --simulate upgrade
E: Unmet dependencies. Try using -f.
$ echo $?
100