Ordinarily, the function to use is ParPath$(), which gives you the full path corresponding to a given argument. However, the documentation for ParPath$() says that it's OS 2.0+ only, so if you require it to run on OS 1.x, that's not going to work. It's a long time since I coded specifically for 1.3, but from memory, under dos.library from 1.x, this is a little tricky to do because ReadArgs and associated functionality was only added in 2.0.
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