Is there a way to get the name of the dmg package an app is started/installed from?
Your question is quite unclear, since I can not figure out what name you want to get. But in any way, the answer will be the same: No, there is no direct way.
Name of the .dmg-file
The name of the .dmg-file is impossible to find out, since the file is mounted as a volume. Usually the mount-point (/Volumes/xxxx) has the name of the .dmg-file, but if the mount-point already exists, the name is extended with a number.
It is possible, that the .dmg-file had a number in the end; so you can not simply drop the number in the end, cause you do not know if it was extended due to the fact, that the mount-point was already in use, or the fact, that the name had a trailing number.
Name of the installer package
Where do you need to find out the name of the installer package? In a Pre- or Postflight-Script? There is not really a simple way to find out the name of the installer-package, but there might be some workarounds to reach the target you want.
UPDATE / Solution:
I found a way, to find out the name of a mounted dmg-file: Run the following command on terminal (can be also done by a script, so that the result can be used within a program):
hdiutil info
The result will look something like this:
================================================
image-path : /Users/username/Downloads/yourDMGFile-v2.0b10.dmg
image-alias : /Users/username/Downloads/yourDMGFile-v2.0b10.dmg
shadow-path : <none>
icon-path : /System/Library/PrivateFrameworks/DiskImages.framework/Resources/CDiskImage.icns
image-type : UDIF, read only, compressed (zlib)
system-image : false
blockcount : 80040
blocksize : 512
writeable : false
autodiskmount : TRUE
removable : TRUE
image-encrypted : false
mounting user : username
mounting mode : <unknown>
process ID : 17177
/dev/disk5 GUID_partition_scheme
/dev/disk5s1 48664310-0200-11FC-ACX1-00360534ACDC /Volumes/yourDMGFile v2.0b10
Here the name of the dmg-file is printed out, as well as the name of the mount-point and further informations about the .dmg-file as well.