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The second best solution is to write a Windows Scripting Host script instead of a batch file since it is much safer to read and parse the registry there.
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The absolute best solution is to call ShellExecuteEx with a forced progid but that is only possible in a real application. html extension to execute a browser and not a HTML editor is somewhat risky as pointed out in another answer but I'm not sure if I would dare to query the registry in a batch-file either. This means you have to give up using the users default browser and I would not recommend it for this reason. If this is not good enough then you can try using IE Automation to start and control Internet Explorer. This does not mean that the browser will respect the anchor but that is a implementation detail in the browser that you have no control over and results might vary depending on which browser is the default. On my system start "" "file:///C:/Program%20Files/Common%20Files/microsoft%20shared/Stationery/Soft%20Blue.htm#whatever" does work as far as accepting the command and starting the browser. A file:// URL will work because Windows only looks at the protocol when dealing with URLs. Just to be clear, appending a anchor to a plain file system path will not work because it technically changes the extension. htm files and/or file:// URLs and this seems to strip away the anchor. In my experience Internet Explorer will sometimes do some kind of internal redirection when dealing with local.
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It does seem to work without quotes as well but I personally prefer them just in case there is a space or a & there.
ATOM FOR MAC OPEN AN .HTML DOC IN BRO WINDOWS 8.1
On my Windows 8.1 machine anchors work fine: start "" "" If you want to start the default browser then you should obviously not hardcode iexplore! The start command will figure out the system default on its own based on the file extension or URL protocol.
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