How to fetch a variable value which name is from another variable in bash

Problem

I want to implement a function like this, I have variables like below, and I want to print the value of ${app}_title, for example, when the app is app1, it will print Application 1, if app is app2, then it will print Application 2.

app1_title="Application 1" 
app2_title="Application 2" 
 
app="app1"

Solution

The implementation is like below:

app_title="${app}_title" 
echo ${!app_title}

In this script, app_title is a variable that holds the string "app1_title". The ${!app_title} syntax is used to get the value of the variable whose name is stored in app_title, which is "Application 1". This feature of bash is called variable indirection.

Full Example

app1_title="Application 1" 
app2_title="Application 2" 
 
app="app1" 
 
if [ ! -z $1 ]; then 
    app="$1" 
fi 
 
app_title_var=${app}_title 
echo "The app title is ${!app_title_var}"

If the bash file is called var.sh , then the output is like below:

$ ./var.sh  
The app title is Application 1 
 
$ ./var.sh app2 
The app title is Application 2