Variables

FS

Field separator.

NR

Number of records.

NF

Number of fields.

FNR

File - Number of records.

(Relative to current file).

$ awk '{print FILENAME, FNR;}' student-marks bookdetails.

student-marks 1

student-marks 2

student-marks 3

student-marks 4

student-marks 5

bookdetails 1

bookdetails 2

bookdetails 3

bookdetails 4

bookdetails 5

OFS

Output field separator.

RS

Record separator.

ORS

Output record separator.

FILENAME.