Using variables for variables in a bourne shell script

1 - background

Based on this Twitter thread: https://twitter.com/DLangille/status/1436388549985771520

In a bourne shell, with VAR=ab and ab=123, can I get at the 123 value using ony VAR and not ab?

e.g. echo $VAR gives ab, but I want 123

It's not ${!VAR} because I think that's bash.

$ echo ${!VAR}
/bin/sh: ${!V...}: Bad substitution

2 - script

#!/bin/sh

INGRESS_JAIL="ingress01"
WEB_JAIL="nginx01"
PG_JAIL="pg01"

DEFAULT_REPO_TREE="130amd64-default-primary"
eval ${INGRESS_JAIL}_REPO_TREE="${DEFAULT_REPO_TREE}"
eval ${WEB_JAIL}_REPO_TREE="${DEFAULT_REPO_TREE}"
eval ${PG_JAIL}_REPO_TREE="130amd64-default-pg13"

JAILS="$INGRESS_JAIL $WEB_JAIL $PG_JAIL"

for jail in ${JAILS}
do
  eval repo_tree=\$${jail}_REPO_TREE
  echo $jail will use $repo_tree
done

3 - output

$ ~/tmp/vars.sh
ingress01 will use 130amd64-default-primary
nginx01 will use 130amd64-default-primary
pg01 will use 130amd64-default-pg13


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