my @foo = ([qw(one two)], [qw(three four)], [qw(five six)]);
# use List::Util 'reduce';
# oops: my $str = reduce {"[$a,$b]"} map { reduce {"[$a,$b]"} @$_ } @foo;
my $str = sprintf "[%s]", join ',', map { sprintf '["%s"]', join '","', @$_} @foo;
print "--- $str ---\n";