Unix in a Nutshell, 4th Edition

Built-in Variables

All awk variables are included in gawk.

Version	Variable	Description
awk	ARGC	Number of arguments on the command line.
	ARGV	An array containing the command-line arguments, indexed from 0 to ARGC - 1.
	CONVFMT	String conversion format for numbers ("%.6g"). (POSIX)
	ENVIRON	An associative array of environment variables.
	FILENAME	Current filename.
	FNR	Like NR, but relative to the current file.
	FS	Field separator (a space).
	NF	Number of fields in current record.
	NR	Number of the current record.
	OFMT	Output format for numbers ("%.6g"). (Pre-POSIX awk used this for string conversion also.)
	OFS	Output field separator (a space).
	ORS	Output record separator (a newline).
	RLENGTH	Length of the string matched by match() function.
	RS	Record separator (a newline).
	RSTART	First position in the string matched by match() function.
	SUBSEP	Separator character for array subscripts ("\034").
	$0	Entire input record.
	$ n	nth field in current record; fields are separated by FS.
gawk	ARGIND	Index in ARGV of current input file.
	BINMODE	Controls binary I/O for input and output files. Use values of 1, 2, or 3 for input, output, or both kinds of files, respectively. Set it on the command line to affect standard input, standard output and standard error.
	ERRNO	A string indicating the error when a redirection fails for getline or if close() fails.
	FIELDWIDTHS	A space-separated ...