Show only changed lines with diff, not newly added lines

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http://stackoverflow.com – I'm curious if there is a way to get only changed lines with diff, not the newly added lines? I mean, let's say I have two files file1 and file2. file1 is: abc=123 def=234 klm=10.10 xyz=6666 file2 is: abc+=123 def=234 klm=10.101 xyz=666 stackoverflow=1000 superuser=2000 wtf=911 what I want is giving a command like diff <parameters> file1 file2 and getting an output like - abc=123 + abc+=123 - klm=10.10 + klm=10.101 - xyz=6666 + xyz=666 Such output is welcomed too: - abc=123 + abc+=123 def=234 - klm=10.10 + klm=10.101 - xyz=6666 + xyz=666 I don't want the stackoverflow=1 (HowTos)