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INSTALL_HOOK=0 perl -MO=Deparse -MB::Hooks::OP::Check::StashChange -e 
+'BEGIN { my $id = B::Hooks::OP::Check::StashChange::register(sub {}) 
+if $ENV{INSTALL_HOOK}; } print split "x", "1x2"'

...
}
print split(/x/, '1x2', 0);
-e syntax OK

INSTALL_HOOK=1 perl -MO=Deparse -MB::Hooks::OP::Check::StashChange -e 
+'BEGIN { my $id = B::Hooks::OP::Check::StashChange::register(sub {}) 
+if $ENV{INSTALL_HOOK}; } print split "x", "1x2"'

...
}
print 'x', '1x2';
-e syntax OK