How to get bash file to echo differently based on user input?

Question

I'm pretty new at shell scripts, but I would like to write a basic script where the bash file will echo a different line of text depending on the user input. For example if the script asks the user "Are you there?" and the user input is "yes" or "Yes" then the script would echo something like "hello!". But if the user input is "no" or "No" the script would echo something else. And finally, if the user input is something other than yes/Yes or no/No, the script would echo "Please answer yes or no". Here is what I have so far:

echo "Are you there?"  
read $input  

if [ $input == $yes ]; then  
    echo "Hello!"  
elif [ $input == $no ]]; then  
    echo "Are you sure?"  
else  
    echo "Please answer yes or no."  
fi  

However, no matter the input, I always get the first response ("Hello!")

Also, I would like to incorporate text to speech (as I have done with other bash file projects using festival). In other bash files I have done it this way:

echo "Hello!"  
echo "Hello!" | festival --tts

Is there a way to incorporate this into the if then/yes no prompt above? Thank you in advance, I'm using this to make simple bash files and to help myself learn.

Answer 1

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.

Answer 2

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.

Answer 3

A third approach would be to assign to a common variable for each case, and in the end act upon that variable. I'm not sure how common this approach is in bash, but in other programming languages it's fairly standard.

Also shopt -s nocasematch in conjunction with [[ for case-insensitive string comparison.
With this also YES and NO are treaded as valid input.

shopt
[[

#!/bin/bash

shopt -s nocasematch

read -p "Are you there?" input  

if [[ "$input" == "yes" ]]; then  
    msg="Hello!"  
elif [[ "$input" == "no" ]]; then  
    msg="Are you sure?"  
else  
    msg="Please answer yes or no."  
fi 

echo $msg
echo $msg | festival --tts