For long and boring reasons, I need to retrieve one environment variable based on the value of another. e.g.
export LOG_PROCESSOR=LOGCOURIER
export LOGCOURIER=/usr/bin/blah
echo ${$LOG_PROCESSOR}
-bash: ${$LOG_PROCESSOR}: bad substitution
How can I get the value /usr/bin/blah echo'd in Bash like this?
Of course after finding nothing on google for ages, I find the answer 3 seconds after posting my question. You do:
> echo ${!LOG_PROCESSOR}
> /usr/bin/logcourier
export LOGCOURIER=/usr/bin/blah
export LOG_PROCESSOR=$LOGCOURIER
echo ${LOG_PROCESSOR}
In addition to indirect parameter expansion, bash 4.3 will have named references.
declare -n LOG_PROCESSOR=LOGCOURIER
After this declaration, a change to one variable results in a change to the other.
If you have access to Python, this can be done like so:
export LOG_PROCESSOR=LOGCOURIER
export LOGCOURIER=/usr/bin/blah
echo $(python -c "import os; print(os.environ[os.environ['LOG_PROCESSOR']])")
> /usr/bin/blah
