If you followed my guide on setting up Tomcat on Mac OS with Homebrew, at some point you may want to update Tomcat to the latest version.

You could stop remove the old version, install the new version, update the symlink then restart the service. You might even get away with leaving the restart to the end. I prefer to install the new version side by side and then flip the symlink just before restarting. This leaves a much smaller downtime window and makes rolling back really easy.

The first step is to update your local formula with the new version info by running the following:

brew edit tomcat

Here's the change I made to move from 7.0.6 to 7.0.8:

diff --git a/Library/Formula/tomcat.rb b/Library/Formula/tomcat.rb
index 90b3443..bded504 100644
--- a/Library/Formula/tomcat.rb
+++ b/Library/Formula/tomcat.rb
@@ -1,9 +1,9 @@
 require 'formula'
 
 class Tomcat <Formula
-  url 'http://archive.apache.org/dist/tomcat/tomcat-7/v7.0.6/bin/apache-tomcat-7.0.6.tar.gz'
+  url 'http://archive.apache.org/dist/tomcat/tomcat-7/v7.0.8/bin/apache-tomcat-7.0.8.tar.gz'
   homepage 'http://tomcat.apache.org/'
-  md5 '1c54578e2e695212ab3ed75170930df4'
+  md5 'b18b0f1d987f82038a7afeb2e3075511'
 
   skip_clean :all

After the formula is updated you can install the new version with:

brew install tomcat

As per the initial install, Homebrew links the keg which results in a handful of generically named scripts being added to your path. We'll need to unlink it.

If you try to unlink with brew unlink tomcat you'll get Error: tomcat has multiple installed versions. It seems the brew command doesn't really like multiple versions of the same formula being installed at the same time and it presently doesn't expose a way to do this other than removing the old version first. We can however unlink it by calling the Homebrew API directly:

ruby -I/usr/local/Library/Homebrew -rglobal -rkeg -e 'puts Keg.new("/usr/local/Cellar/tomcat/7.0.8").unlink'

The next step is to switch out the libexec symlink:

sudo -u tomcat ln -sf /usr/local/Cellar/tomcat/7.0.8/libexec /usr/local/tomcat/

And then restart the service:

sudo launchctl unload -w /Library/LaunchDaemons/org.apache.tomcat.plist
sudo launchctl load -w /Library/LaunchDaemons/org.apache.tomcat.plist

If all goes well, remove the old version (via the API to workaround the brew limitation with multiple versions):

ruby -I/usr/local/Library/Homebrew -rglobal -rkeg -e 'k = Keg.new("/usr/local/Cellar/tomcat/7.0.6"); puts k.unlink; k.uninstall'