If Excel does this, you could find out by simply trying to open the file. It'll fail if it's already open.
Actually, this is not true. Under cygwin perl I was able to open (using open) for writing a file that was currently opened by Excel. Trying to open that same file using WordPad, however, resulted in the familiar "The document ... is in use by another application ..." message.

In reply to Re^2: Finding if a file is open by pc88mxer
in thread Finding if a file is open by merrymonk

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