BEGIN { require bytes; bytes->import if $condition }

##</code><code>##

$foo = $a;
BEGIN { require strict; strict->import if 1 }
$foo = $a;
__END__
Variable "$foo" is not imported at x line 3.
Global symbol "$foo" requires explicit package name at x line 3.
x had compilation errors.

##</code><code>##

$foo = $a;
BEGIN { require strict; strict->import if 0 }
$foo = $a;
__END__