You can still do it with awk, but with different "ergonomics":

  awk -F= '$2 ~ /[0-9]+/ { print $2 }'

With imaginative choice of FS and RS you can push it very far.

Whether other people having to deal with such code will appreciate your imagination is another matter, though.

Edit: I missed the detail where you want to specifically match "foo" as lhs, and anywhere on the line. So the correct condition would be even lengthier : ^ ) You have a valid point. Captures would provide for shorter patterns.