# solution 1
bash-4.2$ perl -lne 'print if (!/(.)(?=$1)/g && /.{10}/)' <<< 'abcdefghij'

# solution 2

bash-4.2$ perl -lne 'print if (!/(.)(?=\1)/g && /.{10}/)' <<< 'a b c d e '
a b c d e

bash-4.2$ perl -lne 'print if (!/(.)(?=\1)/g && /.{10}/)' <<< 'abcdefghij klmno pqrstuvwxyz'
abcdefghij klmno pqrstuvwxyz

# solution 3

bash-4.2$ perl -lne 'print if ( /(.)(?!$1)/g && /.{10}/)' <<< 'abcdefghij'