Advanced tcpdump and Wireshark filter string generator.

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Packetman is a packet capture filter generator modeled after Wireshark's String-Matching Capture Filter Generator but with a lot more features allowing much finer control over the packets you see.


  • String-matching (just like Wireshark's tool)
  • bit-string matching
  • hex-string matching
  • easy masking through ? wildcard characters
  • offsets in bits or bytes
  • use header field name instead of manual offsets
  • application specific queries
  • built-in header reference tables


Add this line to your application's Gemfile:

gem 'packetman'

And then execute:

$ bundle

Or install it yourself as:

$ gem install packetman


$ packetman -h

Usage: packetman [OPTIONS] FILTER_STRING
    -p, --protocol PROTO             Transport Protocol (tcp,udp,icmp)
    -t, --transport                  OFFSET starts at transport header instead of data payload
    -r, --radix RADIX                Treat FILTER_STRING as RADIX instead of String
    -o, --offset OFFSET              Offset in bits
    -b, --byte-offset                Use 8-bit bytes instead of bits for offset
    -w, --wildcard [CHARACTER=?]     Treat CHARACTER as single-character wildcard
    -v, --version                    Show version

Create and use a filter string to capture all HTTP GET requests to /foo/bar

$ sudo tcpdump -nA `packetman GET /foo/bar`
tcpdump: data link type PKTAP
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on pktap, link-type PKTAP (Packet Tap), capture size 262144 bytes
16:49:04.516409 IP > Flags [P.], seq 1488105913:1488105994, ack 1397163988, win 4121, options [nop,nop,TS val 875380202 ecr 2751916352], length 81: HTTP: GET /foo/bar HTTP/1.1
[email protected]@..S..
[email protected] /foo/bar HTTP/1.1
Host: localhost
User-Agent: curl/7.43.0
Accept: */*

Hexadecimal string with wildcards

$ packetman -r 16 -w '?' "A8C401???C200A"
tcp[((tcp[12:1] & 0xf0) >> 2) + 0:4] & 0xffffff00 = 0xa8c40100 && tcp[((tcp[12:1] & 0xf0) >> 2) + 4:2] & 0x0fff = 0x0c20 && tcp[((tcp[12:1] & 0xf0) >> 2) + 6:1] & 0xff = 0x0a

Base 4 string with wildcards and offset beginning at start of the TCP header

$ packetman -t -o 3 -r 4 -w i 1223iiii2212
tcp[0:4] & 0x1fe01fe0 = 0x0d6014c0


After checking out the repo, run bin/setup to install dependencies. Then, run rake rspec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.