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The ports tree has been updated. To upgrade your installed ports, you should run
  port upgrade outdated
bash-3.2# port upgrade outdated
Warning: xcodebuild exists but failed to execute
--->  Extracting zlib
Error: Couldn't determine your Xcode version (from '/usr/bin/xcodebuild -version').
Error: 
Error: If you have not installed Xcode, install it now; see:
Error: http://guide.macports.org/chunked/installing.xcode.html
Error: 
Error: Target org.macports.extract returned: unable to find Xcode
Log for zlib is at: /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_ports_archivers_zlib/zlib/main.log
Error: Unable to upgrade port: 1
To report a bug, see <http://guide.macports.org/#project.tickets>