Usage:

Take a packet data from a log or packet sniffer:

11:31:30.94467 rx: buf 00 (MGMT/Beacon): time 5059409 len 56 signal 42 SNR 0 macstat 25 phystat 10 phyrate 110 status 1
11:31:30.94469 rx: 802.11 buf[56]: 80 00 00 00 FF FF FF FF FF FF 00 09 5B 68 2D 39
11:31:30.94471 00 09 5B 68 2D 39 F0 86 5D B5 3E 25 00 00 00 00
11:31:30.94475 41 01 11 00 00 03 61 63 78 01 04 82 84 8B 96 03
11:31:30.94477 01 0B 05 04 00 01 00 00

or invent your own packet contents.

Then:

printhex \
80 00 00 00 FF FF FF FF FF FF 00 09 5B 68 2D 39 \
00 09 5B 68 2D 39 F0 86 5D B5 3E 25 00 00 00 00 \
41 01 11 00 00 03 61 63 78 01 04 82 84 8B 96 03 \
01 0B 05 04 00 01 00 00 \
| sendpkt wlan0

will send a custom packet with same bytes.

If you wonder, this packet has the following structure:
fc: 0080
dur: 0000
ra: FFFFFFFFFFFF
ta: 00095B682D39
bssid: 00095B682D39
seq: 86F0
timestamp: 00000000253EB55D
bcn_int: 0141
cap_info: 0011
ssid: 00 03 61 63 78 ('acx')
supp_rates: 01 04 82 84 8B 96 (1, 2, 5.5, 11)
ds_parms: 03 01 0B (channel 11)
tim: 05 04 00 01 00 00
