$  perl -Mstrict -Mwarnings -E '
my @arr = q{0} .. q{9};
for my $idx ( grep { $_ % 2 } reverse 0 .. $#arr )
{
    $arr[ $idx - 1 ] .= splice @arr, $idx, 1;
}
say for @arr;'
01
23
45
67
89
$