Manual Pages  — NGHOOK

If the -e option is given, the third argument is interpreted as the path to a program, and this program is executed with the remaining arguments as its arguments. Before executing, the program Netgraph messages (specified by the -m option) are sent to the node. The program is executed with its standard input (unless closed by -n) and output connected to the hook.

If the -e option is not given, all data written to standard input is sent to the node, and all data received from the node is relayed to standard output. Messages specified with -m are sent to the node before the loop is entered. The nghook utility exits when EOF is detected on standard input in this case.

The options are as follows:

-a
	Output each packet read in human-readable decoded ASCII form instead of raw binary.
-d
	Increase the debugging verbosity level.
-e
	Execute the program specified by the third argument.
-l
	Loops all received data back to the hook in addition to writing it to standard output.
-m msg
	Before executing the program (in -e mode) send the given ASCII control message to the node. This option may be given more than once.
-n
	Do not attempt to read any data from standard input. The nghook utility will continue reading from the node until stopped by a signal.
-S
	Use file descriptor 0 for output instead of the default 1.
-s
	Use file descriptor 1 for input instead of the default 0.