I'm trying to create Google App Engine environment in my Mac OS X Mountain Lion. Downloaded the Googleapplauncher.dmg file. While I tried to unzip the file it shows "the following disk images couldn't be opened" . Reason: "Not recognised".
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php
macos
google-app-engine
It's likely that the download was corrupted if you are getting an error with the disk image. Go back to the downloads page at https://developers.google.com/appengine/downloads and look at the SHA1 checksum. Then, go to your Terminal app on your mac and run the following:
openssl sha1 [put the full path to the file here without brackets]
For example:
openssl sha1 /Users/me/Desktop/myFile.dmg
If you get a different value than the one on the Downloads page, you know your file is not properly downloaded and you should try again.
Source: Stackoverflow.com