Many systems, and most GNU/Linux distros, use gawk as their default awk. (Older BSD systems also used gawk as their default awk, until newer BSD systems switched to nawk.) gawk was the only free awk, until the 1991 release of mawk.
A "gawkism" is an extension that works with gawk, but not with other AWK variants. Gawk's own manual identifies GNU extensions, so programmers know which features require gawk.
Some gawkisms are
- GNU-style regular expressions.
- extra built-in functions, like
- Korn-style coprocesses.
- TCP and UDP networking with "/inet/".
- (since gawk 4.0.0) arrays of arrays, like
ary = 4.
- (since gawk 4.0.0) indirect function calls, like
str = "foo"; @str() # calls foo().
- other GNU extensions in the manual.