cannot use assignment expression concatenation (||) in the physical file name of an infile statement.
If the parts are strings, just make it one string.
If some parts are macro variables, enclose all fixed strings and the macro variables in one double quoted(") string.
If any parts are created in a data step variable, then you need to derive a variable holding the concatenated string like[pre] fullName ='me/you/' || variable || 'rest of the file name' ;[/pre] and use the infile option FILEVAR= fullName.
Once you have achieved this concatenation in the relevant way, another infile option FILENAME= {someVarName} will reveal the full path and filename from which the current infile buffer has been loaded.
worth playing around with. For the only example of FILENAME= at support.sas.com, see INFILE example 5 at
http://support.sas.com/documentation/cdl/en/lrdict/61724/HTML/default/a000146932.htm#a000177201 .
good luck
PeterC