sub doit
{
 my @array = qw(1 2 3 4);
 # this doesn't damage outer @array:
 $_ = 'xyz' foreach (@array);
}

my @array = qw(a b c d);
print join("|", @array), "\n";

foreach (@array)
{
 my $f = doit('abcd');
}

print join("|", @array), "\n";