This tutorial sums up how to slipstream content into OSX packages (pkg files). The tutorial works on the GrowlMail.pkg package with is meant to install GrowlMail which is incompatible with newer versions of Mail.app under Snow Leopard.

• The GrowlMail.pkg package is placed on the desktop.

cd ~/Desktop/
pkgutil --expand GrowlMail.pkg GrowlMail

cd GrowlMail/growlmail.pkg
cat Payload | gzip -d | cpio -id
mkdir ~/Desktop/Bundle
mv GrowlMail.mailbundle ~/Desktop/Bundle
cd ~/Desktop/Bundle

Now you can edit the files or add new files. In this case, we add:

                <string>588FF7D1-4310-4175-9980-145B7E975C02</string>          
                <string>064442B6-53C0-4A97-B71B-2F111AE4195B</string>

to the ~/Desktop/Bundle/GrowlMail.mailbundle/Contents/Info.plist file.

cd ~/Desktop/Bundle
find . | cpio -o --format odc | gzip -c > ~/Desktop/GrowlMail/growlmail.pkg/Payload
mkbom ./ ~/Desktop/GrowlMail/growlmail.pkg/Bom

Still in ~/Desktop/Bundle we issue:

du -sk 

and then edit ~/Desktop/GrowlMail/growlmail.pkg/PackageInfo and modify the line:

    <payload installKBytes="1288" numberOfFiles="60"/>

so that installKBytes is the value we obtained with du -sk minus 4 (assuming that the disk is using 4KB blocks).

The result is thus:

    <payload installKBytes="1300" numberOfFiles="60"/>

Additionally, if we had added or removed files, we have to issue:

find ~/Desktop/Bundle/ | wc 

and update ~/Desktop/GrowlMail/growlmail.pkg/PackageInfo to change numberOfFiles which represents the total number of nodes (files, directories, sockets, etc…) including ..

cd ~/Desktop
rm GrowlMail.pkg
pkgutil --flatten GrowlMail GrowlMail.pkg

The result is the following package that makes GrowlMail compatible with Snow Leopard including the latest security updates that made GrowlMail incompatible with Mail.app.

• GrowlMail.pkg