variable substitution (what do you call/name this method)?

Question

Say in bash I have:

c=3

b3=4

instead of:

echo $b3 

what kinda of command to have output of "4" ? I tried below but couldn't.

1. echo $b($(c))

2. echo $b{!c}

3. echo $b${c}

4. echo ${d[$c]}

Answer 1

You can use an indirect reference for that:

$ c=3
$ b3=4
$ d=b$c
$ echo "${!d}"
4

Although usually instead of indirect references, arrays should be used when possible.