Dynamic Bash Variable Names

I found myself in the middle of a rather large Bash project a little while back. Basically, I had defined several file paths in variable names and needed to access that information dynamically.

The scenario is this: a value would be supplied by the user, and I had to pull out some hard-wired information based on this value. So, suppose you were writting a script that referenced file types arranged by extenstions and was selected by the user at run time. This would be easily solvable in the following:

#!/usr/bin/env bash

# List of variables maybe in some other file
JPG_FILE_PATH="/opt/path/one"
DOC_FILE_PATH="/opt/path/two"
MP3_FILE_PATH="/opt/path/three"
XLS_FILE_PATH="/opt/path/four"

get_file_path() {
    local ID=${1-''}
    # Sets FILE_PATH to the desired value. If not exist then null.
    FILE_PATH=$(eval "echo \${$(echo ${ID}_FILE_PATH)"-''})
}

get_file_path "MP3" 
echo $FILE_PATH

$ ./test_pre.sh
/opt/path/three

The above snippet -- admittedly a bit humorous -- is very useful in several situations. I happened to use it in creating a shell library of functions and paths that are used by others in the easy creation of scripts around Oracle RDBMS.