See section Extensions in
gawk Not in POSIX
for a summary of the GNU extensions to the
awk language and program.
All of these features can be turned off by invoking
gawk with the
--traditional option or with the --posix option.
gawk is compiled for debugging with ‘-DDEBUG’, then there
is one more option available on the command line:
Print out the parse stack information as the program is being parsed.
This option is intended only for serious
and not for the casual user. It probably has not even been compiled into
your version of
gawk, since it slows down execution.