LINEIN(testdata.txt,1,1)
reads the first line from "testdata.txt".
LINEIN(testdata.txt)
reads one line from "testdata.txt" at the current read position.
LINEIN(testdata.txt,,0)
reads no line from "testdata.txt" at the current read position.
VarString = linein(testdata.txt)
assigns one line of text read from "testdata.txt" to the variable VarString.