Create an SSIS package that processes the file;
whether the procedure calls CLR to process the file, or you load the file contents into a SQL table via that SSIS package , and then call the stored procedure is up to you.
then you can have a job that calls that SSIS package every x minutes, across a schedule when you might expect the file.
(ie i expect the file M-F somewhere between 4 am and 7 am, execute the package every ten minutes.)
you use a foreach loop to go through all files int he folder, even if you expect there to be only one.
that way, no files means the package exits quickly when no files found.
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