Built-in Variables (The GNU Awk User’s Guide)

From Get docs
Gawk/docs/latest/Built 002din-Variables

7.5 Predefined Variables

Most awk variables are available to use for your own purposes; they never change unless your program assigns values to them, and they never affect anything unless your program examines them. However, a few variables in awk have special built-in meanings. awk examines some of these automatically, so that they enable you to tell awk how to do certain things. Others are set automatically by awk, so that they carry information from the internal workings of awk to your program.

This section documents all of gawk’s predefined variables, most of which are also documented in the chapters describing their areas of activity.

User-modified    Built-in variables that you change to control awk.
Auto-set    Built-in variables where awk gives you information.
ARGC and ARGV    Ways to use ARGC and ARGV.