In bash v4 you can use a "nameref"

$ foobar_darwin_amd64=pinto
$ package=foobar
$ declare -n var=${package}_darwin_amd64
$ echo $var
pinto
# and .....
echo ${!var}
foobar_darwin_amd64

In bash v4 you can use a "nameref"

$ foobar_darwin_amd64=pinto
$ package=foobar
$ declare -n var=${package}_darwin_amd64
$ echo "$var"
pinto

The variable name you constructed can be obtained with the indirect variable expansion syntax:

$ echo "${!var}"
foobar_darwin_amd64

In bash v4 you can use a "nameref"

$ foobar_darwin_amd64=pinto
$ package=foobar
$ declare -n var=${package}_darwin_amd64
$ echo $var
pinto

In bash v4 you can use a "nameref"

$ foobar_darwin_amd64=pinto
$ package=foobar
$ declare -n var=${package}_darwin_amd64
$ echo $var
pinto
# and .....
echo ${!var}
foobar_darwin_amd64