Searches for a file on the system environment path
findonpath(fn, status = TRUE, quote = TRUE)
The filename to search for (without a path)
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Enclose returned filename in quotes
The full path and name of the found file, or NULL if not found
This will return the first found occurence of file fn
, searching 1) the current working directory, 2) the user's R 'home' directory,
then 3) the directories on the operating system environment 'path'