while [ 0 ]
        do
                if [[ "$word" == [a-z]+ ]]
                then
                        word=$(echo $word | tr "[A-Z]" "[a-z]")
                        encrypted=$(echo $word | tr "[a-z]" "-")
                        display $encrypted $word
                        break
                else
                        echo "Please enter a word consisting of only the letters a-z."
                        read word
                fi
        done

bash-2.03$ x="abc"
bash-2.03$ [[ $x == [a-z]+ ]] && echo it matches
bash-2.03$ x="d+"
bash-2.03$ [[ $x == [a-z]+ ]] && echo it matches
it matches
bash-2.03$

#!/bin/bash3 -

# @(#) s1       Demonstrate extended glob matching.
# See man bash "Pattern matching" and extglob shopt.

echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version =o $(_eat $0 $1)

x="abc"
if [[ $x == [a-z]+ ]]
then
  echo " Matched trailing +."
fi

shopt -s extglob
if [[ $x == +([a-z]) ]]
then
  echo " Matched leading +."
fi

exit 0

% ./s1
(Versions displayed with local utility "version")
Linux 2.6.11-x1
GNU bash 3.00.16(1)-release
 Matched leading +.