NR: sequence number of the current input record. The entire value of the current input record.
NF: the number of fields in the current record.
$1-$N: ordered fields in the current record.
FS: input field delimiter (white space—tab or space—by default).
OFS: output field separator (space character by default).
RS: input record delimiter (newline by default).
ORS: output record delimiter (newline by default).
FILENAME: current input file name. When reading from standard input, FILENAME is set to - (dash).
