$Line
is a global variable that specifies the number of the current input line.
Examples
Wolfram Research (1988), $Line, Wolfram Language function, https://reference.wolfram.com/language/ref/$Line.html.
Text
Wolfram Research (1988), $Line, Wolfram Language function, https://reference.wolfram.com/language/ref/$Line.html.
CMS
Wolfram Language. 1988. "$Line." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/$Line.html.
APA
Wolfram Language. (1988). $Line. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/$Line.html