You'll need to do the ReadLine() just once in each iteration of the loop so that you don't get the P1 from one line pairing with the P2 from the next line, something like this:

set file=##class(%Stream.FileCharacter).%New()

do file.LinkToFile("c:\location of csv")

for  quit:file.AtEnd  set line=file.ReadLine() set ^GLOBAL($piece(line,",",1),$piece(line,",",*))=""
 

Many command line utilities are listed and documented in the legacy documentation:

https://cedocs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=GDOC_legacy
 

Or

USER>k temp  set $LIST(temp,31)="",myVar=$LISTTOSTRING(temp,"=?",1)
USER>w myVar
=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?=?