use Algorithm::FastPermute;
my @c = ('a'..'c');
for my $i (0..2) {
    for my $j (0..2) {
        my @c = @c[$i..$j] if $i <= $j;
        permute {print @c , "\n"} @c;
    }
}

__END__
a
ab
ba
abc
acb
cab
bac
bca
cba
b
bc
cb
c
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