tcap: Tcl pcap interface


1. install

edit the makefile for your local paths, then run "make install" as root or via sudo

2. use:

   $ tclsh
   % package require tcap
   % tcap help
    tcap - Tcl pcap(3) interface
              list all available devices.
            open dev promisc snaplen
              opens a new packet capture interface.
              returns the datalink offset in byes.
            filter bpg_program
              sets a bpf(3) filter on the pcap interface.
              returns the next packet as a list of bytes.
              closes the capture interface.

3. more? see test.tcl for some info on how to use tcap

a minimal sniffer in Tcl using tcap:

 #!/usr/bin/env tclsh

 package require tcap

 tcap open fxp0 0 1500
 set dl [tcap dloff]
 tcap filter "tcp"
 while {1} {
         set g [tcap get]
         if {[llength [split $g]] > 0} {
                 puts [lrange $g $dl end]
 tcap close

Tcap was built and tested on BSD UNIX and MacOS X, and should work on Linux. Testing on Windows is incomplete.

Tcap uses a couple of routines from Dug Song's dsniff utility to streamline the pcap interface. As a result, tcap open lets you call an interface or a file for parsing.

The tcap command is global, so use Tcl namespaces to have more than one sniffer active.

The pcap_inject() command is not implemented. For writing packets in Tcl look up Clif Flynt's Packet Master library (a Tcl interface to libdnet). Very useful when combined with tcap. URL:

Also see pktsrc, the (formerly) QACafe Tcl packet creation and capture utility.

baski - 2010-02-19 21:52:02

Hi Jose,

I compiled your tcap tool in linux fedora core but 'tcap get' always returns two hex chars are the output. thanks