While all the platforms I tested (Linux 2.6, Solaris, and Windows XP) have the case sensitive environment variable table, Windows batch script handles environment variable in the case preserving but case insensitive way (that is, cmd.exe can get both FOO and foo as environment variables when it's launched, and the "set" command will display it accordingly, but "echo %foo%" results in echoing the value of "FOO", not "foo" — this is presumably caused by the behavior of the underlying Win32 API GetEnvironmentVariable acting in case insensitive way.) Windows users are also used to write environment variable case-insensitively (like %Path% vs %PATH%), and you can see many documents on the web that claims Windows environment variables are case insensitive.
So for a consistent cross platform behavior, it creates the least confusion to make the table case insensitive but case preserving.
In Jenkins, often we need to build up "environment variable overrides" on master, then to execute the process on slaves. This causes a problem when working with variables like PATH. So to make this work, we introduce a special convention PATH+FOO — all entries that starts with PATH+ are merged and prepended to the inherited PATH variable, on the process where a new process is executed. @author Kohsuke Kawaguchi
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