You can use indirect parameter expansion (see man bash):
If the first character of parameter is an exclamation point (!), it
introduces a level of variable indirection. Bash uses the value of the
variable formed from the rest of parameter as the name of the variable;
this variable is then expanded and that value is used in the rest of
the substitution, rather than the value of parameter itself. This is
known as indirect expansion. The exceptions to this are the expansions
of ${!prefix*} and ${!name[@]} described below. The exclamation point
must immediately follow the left brace in order to introduce indirec-
tion.
That is:
for i in 1 2; do var="TEST_$i"; echo "${!var}"; done
Test:
$ TEST_1=12345
$ TEST_2=54321
$ for i in 1 2; do var="TEST_$i"; echo "${!var}"; done
12345
54321
