Bash Shell Script: How can I restrict getopts so that it only takes one type of option?

Question

I am using getopts and for the options I want to accept just one type of letter but it can be passed multiple times. Can't figure out how to do this but it should work the way ls -l does where that ls -lllllll and ls -l -l -l -l -l all return the same thing and it only runs once.

while getopts ":abc" opt; do
        case "$opt" in
                a) echo "a"
                ;;
                b) echo "b"
                ;;
                p) echo "c"
                ;;
                ?) echo "error"
                ;;
        esac
done

so in this example, I want ./program.sh -a, ./program.sh -aaaaaaa (with any number of as), and ./program.sh -a -a -a -a to all return "a" just one time and then something like ./program.sh -ab or ./program.sh -abc or ./program.sh -a -c to return an error

Answer 1

Don't take action while parsing your options. Just record which options are seen, and take action afterwards.

while getopts ":abc" opt; do
        case "$opt" in
                a) A=1
                ;;
                b) B=1
                ;;
                c) C=1
                ;;
                ?) echo "error"
                ;;
        esac
done

if ((A + B + C > 1)); then
    printf 'Only one of -a, -b, -c should be used.\n' >&2
    exit 1;
fi

[[ $A == 1 ]] && echo "a"
[[ $B == 1 ]] && echo "b"
[[ $C == 1 ]] && echo "c"

Answer 2

You have to write the logic yourself to handle multiple invocations of the same argument.

A=0
while getopts ":a" option; do
        case "$option" in
                a) [[ $A != 1 ]] && echo "a" 
                   A=1
                ;;
                *) echo "error"
                ;;
        esac
done