Making git show to show information in a machine parseable format
Solution 1:
git cat-file tag <tag_name>
will give you the actual contents of the file that represents that tag (helpfully unpacked and uncompressed).
Example
$ git init
$ touch README
$ git add README
$ git commit -m 'Initial commit'
$ git tag -a foo -m 'Tagging foo'
$ git cat-file tag foo
object 91654534f5ac138a3adb56a9e6dc3bacae5bae53
type commit
tag foo
tagger Peter Lundgren <[email protected]> 1369779403 -0400
Tagging foo