How to ask a [Y/n] question in bash script? [duplicate]

The main problem is here:

read $input

In bash, usually, $foo is the value of the variable foo. Here, you don't want the value, but the name of the variable, so it should be just:

read input

Similarly, in the if tests, $yes and $no should be just yes and no, since you just want the strings yes and no there.

You could use a case statement here, which (IMHO) makes it easier to do multiple cases based on input:

case $input in
[Yy]es)    # The first character can be Y or y, so both Yes and yes work
    echo "Hello!"  
    echo "Hello!" | festival --tts
    ;;
[Nn]o)     # no or No
    echo "Are you sure?"
    echo "Are you sure?" | festival --tts
    ;;
*)         # Anything else
    echo "Please answer yes or no."
    echo "Please answer yes or no." | festival --tts
    ;;
esac

You could wrap the two echo statements and the use of festival in a function to avoid repeating yourself:

textAndSpeech ()
{
    echo "$@"
    echo "$@" | festival --tts
}
case $input in
[Yy]es)    # The first character can be Y or y, so both Yes and yes work
    textAndSpeech "Hello!"  
    ;;
[Nn]o)     # no or No
    textAndSpeech "Are you sure?"
    ;;
*)         # Anything else
    textAndSpeech "Please answer yes or no."
    ;;
esac

With $input, bash replaces this with its value, which is nothing initially, so the read command run is:

read 

And read by default stores the input in the variable REPLY. So you can, if you want, eliminate the input variable altogether and use $REPLY instead of $input.

Also have a look at the select statement in Bash.

TL;DR: fix syntax errors, ensure you actually have non-empty variables in [ test, and make a function to pipe through tee into festival.

As far as printing to screen and outputting to festival, I personally would wrap the script into a function and pipe everything to festival, with tee in between (which sends text both to screen and pipe).

There's three syntax problems to fix, however:

• read $input should be read input. The $ symbol dereferences variable in shell scripting (i.e., it $input will be replaced with what input holds).
• You've no yes and no variables declared. What you should be doing is string comparison: [ "$input" == "yes" ]
• Extra ]] in elif

As for why you get Hello! all the time, that's exactly because of first two bullet points. Before read $input the variable input doesn't exist, so you're only performing read (i.e., nonexistent variable $input is dereferenced into empty string, leaving only read command there). So whatever you type gets stored in the REPLY variable which is what read uses when no variable name has been given. And because yes variable doesn't exist, that gets replaced with empty string too. Thus in reality [ $input == $yes ] is treated as [ "" == "" ] which is always true.

$ [ $nonexistent == $anothernonexistent  ] && echo "Success"
Success

The fixed script should be as so:

#!/bin/bash
main(){
    read -p "Are you there?" input  

    if [ "$input" == "yes" ]; then  
        echo "Hello!"  
    elif [ "$input" == "no" ]; then  
        echo "Are you sure?"  
    else  
        echo "Please answer yes or no."  
    fi 
}
main | tee /dev/tty | festival --tts

Remember to quote the variables and read up on difference between = and == in test command.