Você pode tentar a seguinte função bash
#!/bin/bash
function get_password(){
echo "Enter wour password: "
read password
if [[ -n "$password" ]]; then
a=$(echo $password | tr -d "\n" | wc -c)
b=$(echo $password | tr -cd "[:alnum:]" | wc -c)
if [[ $a != $b ]]; then
echo "Plz enter alphanumeric words"
echo "Retry or Press Ctrl + C to exit"
get_password
else
echo "it is fine"
exit 0
fi
else
echo "password can't be left empty"
echo "Retry or Press Ctrl + C to exit"
get_password
fi
}
get_password
Como funciona:
./script.sh
Enter wour password:
12%
Plz enter alphanumeric words
Retry or Press Ctrl + C to exit
Enter wour password:
^C
./script.sh
Enter wour password:
123sddf
it is fine