Bash script - Calling back variables

Question

I’m trying to learn a few things about scripting and Linux systems, so I started learning bash scripting.

For an exercise, I’m trying to program a script that would install all programs that user chooses.

I worked out a skeleton of installation part, but I’m stuck at determining users answer.

Here is my code:

#!/bin/bash

declare -a instal_list=("Gimp" "VLC" "Gedit")

for ((i=0; i<3; i++))
do

echo "Do you want to install ${instal_list[i]} ?"
echo
read answer_${instal_list[i]}

if [[ $answer_${instal_list[i]} == "yes" ]] || [[ $answer_${instal_list[i]} == "Yes" ]] || [[ $answer_${instal_list[i]} == "YES" ]];
then

 instal+=" ${install_list[i]}"

fi

done

My problem is in my if statement. Inside of it, I’m trying to evaluate if users answer is yes. Problem is in answer_${instal_list[i]} variable.

I don't know how to explain what I mean, so I will try to explain it on example.

Example :

We run the script, and the script asks us if we want install Gimp.
We say yes, and the script stores that answer in variable "answer_${instal_list[1]}" ("answer_Gimp").
My problem is when I try to call back that variable ("answer_Gimp"). = To call it I use "$answer_${instal_list[1]}" line, but the shell doesn’t recognize that command as answer_Gimp.

So how can I call back variable answer_${instal_list[1]} so that shell would recognize it as "answer_Gimp"?

If you're using bash 4.x, it has associative arrays. That would be better than indirect variables like this. — Barmar
– Barmar, Commented May 10, 2014 at 1:22
An associative array is an array that uses strings as indexes, instead of just numbers. So you can have ${answer[${instal_list[$i]}]}. — Barmar
– Barmar, Commented May 10, 2014 at 1:30
I think that I understand now. So I would have to declare two arrays at the beginning ( declare -a instal_list and declare -A answer_ ) ? — rkaracic
– rkaracic, Commented May 10, 2014 at 1:42
So my IF should look like this : if [[ ${answer_[${instal_list[i]}]} == "yes" ]] || [[ ${answer_[${instal_list[i]}]} == "Yes" ]] || [[ ${answer_[${instal_list[i]}]} == "YES" ]]; — rkaracic
– rkaracic, Commented May 10, 2014 at 1:55

that other guy · Accepted Answer · 2014-05-10 01:17:27Z

1

thing="Gimp"
answer_Gimp="Yes"

variableName="answer_$thing"
echo "The value of $variableName is ${!variableName}"

answered May 10, 2014 at 1:17

that other guy

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Comments

glenn jackman · Accepted Answer · 2014-05-10 02:55:10Z

0

If you have bash version 4, you can use an associative array:

declare -a instal_list=("Gimp" "VLC" "Gedit")
declare -a to_install
declare -A answers

for prog in "${instal_list[@]}"; do
    read -p "Do you want to install $prog? [y/n] " answer["$prog"]
    if [[ "${answer["$prog"],,}" == y* ]]; then
        to_install+=( "$prog" )
    fi
done

echo you want to install:
printf "   %s\n" "${to_install[@]}"

Looking at that, I don't see why you need to keep the answers in an array. But if you do, that's how you'd do it.

answered May 10, 2014 at 2:55

glenn jackman

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