Question

Some may have found out that in Ubuntu when you install or update via terminal

you get a question similar to

“do you with to install or remove package [Y/n]?”

when you press enter its like its the same as when you type “Y” or “y”

So i was wondering how to make that in bash
This is what i have so far?

echo "question?[Y/n]"
read choose
if [ $choose ~= "Y" ] [ $choose ~= "y" ] [ $choose ~= "" ]
then 
#code
fi

Answer 1

Classically (meaning it will work in POSIX-ish shells other than bash), you’d write:

echo "Question? [Y/n]"
read choose
if [ "$choose" = "Y" ] || [ "$choose" = "y" ] || [ -z "$choose" ]
then 
    # code
fi

The quotes ensure that the test operator see an argument even if $choose is an empty string.

The [[ operator seems to allow you to get away without quoting strings, but is not part of a POSIX shell. POSIX recognizes its existence by noting:

The following words may be recognized as reserved words on some implementations (when none of the characters are quoted), causing unspecified results:

[[    ]]    function    select

If you want the shell to leave the cursor on the same line as the prompt, you can use:

printf "Question? [Y/n] "

POSIX shells recognize the \c escape; bash does not:

echo "Question? [Y/n] \c"

(There may be a way to make bash handle that, but printf is probably more portable.)