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NGREP(8)			 User Manuals			      NGREP(8)

NAME
       ngrep - network grep

SYNOPSIS
       ngrep  <-hNXViwqpevxlDtTRM> <-IO pcap_dump > < -n num > < -d dev > < -A
       num > < -s snaplen > < -S limitlen > < -W normal|byline|single|none > <
       -c cols > < -P char > < -F file > < match expression > < bpf filter >

DESCRIPTION
       ngrep  strives  to provide most of GNU grep's common features, applying
       them to the network layer.  ngrep is a pcap-aware tool that will	 allow
       you  to specify extended regular expressions to match against data pay‐
       loads of packets.  It currently recognizes TCP,	UDP  and  ICMP	across
       Ethernet, PPP, SLIP, FDDI and null interfaces, and understands bpf fil‐
       ter logic in the same fashion as more  common  packet  sniffing	tools,
       such as tcpdump(8) and snoop(1).

OPTIONS
       -h     Display help/usage information.

       -N     Show  sub-protocol number along with single-character identifier
	      (useful when observing raw or unknown protocols).

       -X     Treat the match expression as a  hexadecimal  string.   See  the
	      explanation of match expression below.

       -V     Display version information.

       -i     Ignore case for the regex expression.

       -w     Match the regex expression as a word.

       -q     Be quiet; don't output any information other than packet headers
	      and their payloads (if relevant).

       -p     Don't put the interface into promiscuous mode.

       -e     Show  empty  packets.   Normally	empty  packets	are  discarded
	      because  they  have  no  payload to search.  If specified, empty
	      packets will be shown, regardless of the specified regex expres‐
	      sion.

       -v     Invert the match; only display packets that don't match.

       -x     Dump packet contents as hexadecimal as well as ASCII.

       -l     Make stdout line buffered.

       -D     When reading pcap_dump files, replay them at their recorded time
	      intervals (mimic realtime).

       -t     Print a timestamp in  the	 form  of  YYYY/MM/DD  HH:MM:SS.UUUUUU
	      everytime a packet is matched.

       -T     Print a timestamp in the form of +S.UUUUUU, indicating the delta
	      between packet matches.  Specify a second time to	 indicate  the
	      delta since the first packet match.

       -R     Do not try to drop privileges to the DROPPRIVS_USER.

	      ngrep  makes  no	effort	to validate input from live or offline
	      sources as it is focused more on performance and handling	 large
	      amounts of data than protocol correctness, which is most often a
	      fair assumption to make.	However, sometimes it matters and thus
	      as a rule ngrep will try to be defensive and drop any root priv‐
	      ileges it might have.

	      There exist scenarios where this behaviour can become an	obsta‐
	      cle, so this option is provided to end-users who want to disable
	      this feature, but must do so with an understanding of the risks.
	      Packets  can be randomly malformed or even specifically designed
	      to overflow sniffers and take control of them, and revoking root
	      privileges  is  currently the only risk mitigation ngrep employs
	      against such an attack.  Use this option and turn it off at your
	      own risk.

       -c cols
	      Explicitly set the console width to ``cols''.  Note that this is
	      the console width, and not the full width of what	 ngrep	prints
	      out  as  payloads;  depending on the output mode ngrep may print
	      less than ``cols'' bytes per line (indentation).

       -F file
	      Read in the bpf filter from the specified filename.  This	 is  a
	      compatibility  option  for  users familiar with tcpdump.	Please
	      note that specifying ``-F'' will override any bpf filter	speci‐
	      fied on the command-line.

       -P char
	      Specify  an alternate character to signify non-printable charac‐
	      ters when displayed.  The default is ``.''.

       -K num Kill matching TCP connections (like tcpkill).  The numeric argu‐
	      ment controls how many RST segments are sent.

       -W normal|byline|single|none
	      Specify  an alternate manner for displaying packets, when not in
	      hexadecimal mode.	 The ``byline''	 mode  honors  embedded	 line‐
	      feeds, wrapping text only when a linefeed is encountered (useful
	      for observing HTTP transactions, for  instance).	 The  ``none''
	      mode doesn't wrap under any circumstance (entire payload is dis‐
	      played on one line).  The ``single'' mode	 is  conceptually  the
	      same  as	``none'',  except  that	 everything  including	IP and
	      source/destination  header  information  is  all	on  one	 line.
	      ``normal''  is  the  default  mode and is only included for com‐
	      pleteness.  This option is incompatible with ``-x''.

       -s snaplen
	      Set the bpf caplen to snaplen (default 65536).

       -S limitlen
	      Set the upper limit on the size of packets that ngrep will  look
	      at.   Useful  for	 looking  at only the first N bytes of packets
	      without changing the BPF snaplen.

       -I pcap_dump
	      Input file pcap_dump into ngrep.	Works with any pcap-compatible
	      dump  file  format.   This  option is useful for searching for a
	      wide range of different patterns over the same packet stream.

       -O pcap_dump
	      Output matched packets to a  pcap-compatible  dump  file.	  This
	      feature does not interfere with normal output to stdout.

       -n num Match only num packets total, then exit.

       -d dev By  default  ngrep will select a default interface to listen on.
	      Use this option to force ngrep to listen on interface dev.

       -A num Dump num packets of trailing context after matching a packet.

	match expression
	      A match expression is either an extended regular expression,  or
	      if the -X option is specified, a string signifying a hexadecimal
	      value.  An extended regular  expression  follows	the  rules  as
	      implemented  by  the GNU regex library.  Hexadecimal expressions
	      can optionally be preceded by `0x'.  E.g., `DEADBEEF',  `0xDEAD‐
	      BEEF'.

	bpf filter
	      Selects a filter that specifies what packets will be dumped.  If
	      no bpf filter is given, all IP  packets  seen  on	 the  selected
	      interface will be dumped.	 Otherwise, only packets for which bpf
	      filter is `true' will be dumped.

       The bpf filter consists of one or more primitives.  Primitives  usually
       consist	of  an id (name or number) preceded by one or more qualifiers.
       There are three different kinds of qualifier:

       type   qualifiers say what kind of thing the id name or	number	refers
	      to.  Possible types are host, net and port.  E.g., `host blort',
	      `net 1.2.3', `port 80'.  If there is no type qualifier, host  is
	      assumed.

       dir    qualifiers  specify  a  particular  transfer direction to and/or
	      from id.	Possible directions are src, dst, src or dst  and  src
	      and  dst.	  E.g.,	 `src  foo', `dst net 1.2.3', `src or dst port
	      ftp-data'.  If there is no dir qualifier, src or dst is assumed.
	      For  `null'  link	 layers (i.e. point to point protocols such as
	      slip) the inbound and outbound qualifiers can be used to specify
	      a desired direction.

       proto  qualifiers are restricted to ip-only protocols.  Possible protos
	      are: tcp , udp and icmp.	e.g., `udp src foo' or `tcp port  21'.
	      If  there	 is  no proto qualifier, all protocols consistent with
	      the type are assumed.  E.g., `src foo' means `ip	and  ((tcp  or
	      udp)  src	 foo)',	 `net bar' means `ip and (net bar)', and `port
	      53' means `ip and ((tcp or udp) port 53)'.

       In addition to the above, there are some special	 `primitive'  keywords
       that  don't  follow  the pattern: gateway, broadcast, less, greater and
       arithmetic expressions.	All of these are described below.

       More complex filter expressions are built up by using the words and, or
       and  not to combine primitives.	E.g., `host blort and not port ftp and
       not port ftp-data'.  To save typing, identical qualifier lists  can  be
       omitted.	 E.g., `tcp dst port ftp or ftp-data or domain' is exactly the
       same as `tcp dst port ftp or tcp dst port  ftp-data  or	tcp  dst  port
       domain'.

       Allowable primitives are:

       dst host host
	      True  if	the  IP destination field of the packet is host, which
	      may be either an address or a name.

       src host host
	      True if the IP source field of the packet is host.

       host host
	      True if either the IP source or destination  of  the  packet  is
	      host.   Any  of the above host expressions can be prepended with
	      the keywords, ip, arp, or rarp as in:
		   ip host host
	      which is equivalent to:

       ether dst ehost
	      True if the ethernet destination address is ehost.  Ehost may be
	      either  a	 name from /etc/ethers or a number (see ethers(3N) for
	      numeric format).

       ether src ehost
	      True if the ethernet source address is ehost.

       ether host ehost
	      True if either the ethernet source  or  destination  address  is
	      ehost.

       gateway host
	      True  if	the packet used host as a gateway.  I.e., the ethernet
	      source or destination address was host but neither the IP source
	      nor  the	IP destination was host.  Host must be a name and must
	      be found in both /etc/hosts  and	/etc/ethers.   (An  equivalent
	      expression is
		   ether host ehost and not host host
	      which  can  be  used  with  either  names	 or numbers for host /
	      ehost.)

       dst net net
	      True if the IP destination address of the packet has  a  network
	      number  of net. Net may be either a name from /etc/networks or a
	      network number (see networks(4) for details).

       src net net
	      True if the IP source address of the packet has a network number
	      of net.

       net net
	      True  if	either	the  IP	 source	 or destination address of the
	      packet has a network number of net.

       net net mask mask
	      True if the IP address matches net with  the  specific  netmask.
	      May be qualified with src or dst.

       net net/len
	      True if the IP address matches net a netmask len bits wide.  May
	      be qualified with src or dst.

       dst port port
	      True if the packet is ip/tcp or ip/udp  and  has	a  destination
	      port  value of port.  The port can be a number or a name used in
	      /etc/services (see tcp(4P) and udp(4P)).	If  a  name  is	 used,
	      both  the	 port number and protocol are checked.	If a number or
	      ambiguous name is used, only the port number is  checked	(e.g.,
	      dst port 513 will print both tcp/login traffic and udp/who traf‐
	      fic, and port domain will print both tcp/domain  and  udp/domain
	      traffic).

       src port port
	      True if the packet has a source port value of port.

       port port
	      True  if	either the source or destination port of the packet is
	      port.  Any of the above port expressions can be  prepended  with
	      the keywords, tcp or udp, as in:
		   tcp src port port
	      which matches only tcp packets whose source port is port.

       less length
	      True  if	the  packet has a length less than or equal to length.
	      This is equivalent to:
		   len <= length.

       greater length
	      True if the packet has a length greater than or equal to length.
	      This is equivalent to:
		   len >= length.

       ip proto protocol
	      True if the packet is an ip packet (see ip(4P)) of protocol type
	      protocol.	 Protocol can be a number or one of the names tcp, udp
	      or  icmp.	  Note	that the identifiers tcp and udp are also key‐
	      words and must be escaped via backslash (\), which is \\ in  the
	      C-shell.

       ip broadcast
	      True  if	the  packet  is an IP broadcast packet.	 It checks for
	      both the all-zeroes  and	all-ones  broadcast  conventions,  and
	      looks up the local subnet mask.

       ip multicast
	      True if the packet is an IP multicast packet.

       ip     Abbreviation for:
		   ether proto ip

       tcp, udp, icmp
	      Abbreviations for:
		   ip proto p
	      where p is one of the above protocols.

       expr relop expr
	      True  if the relation holds, where relop is one of >, <, >=, <=,
	      =, !=, and expr is an arithmetic expression composed of  integer
	      constants	 (expressed  in	 standard C syntax), the normal binary
	      operators [+, -, *, /, &, |], a  length  operator,  and  special
	      packet  data  accessors.	 To access data inside the packet, use
	      the following syntax:
		   proto [ expr : size ]
	      Proto is one of ip, tcp, udp or icmp, and indicates the protocol
	      layer for the index operation.  The byte offset, relative to the
	      indicated protocol layer, is given by expr.   Size  is  optional
	      and  indicates  the number of bytes in the field of interest; it
	      can be either one, two, or  four,	 and  defaults	to  one.   The
	      length  operator, indicated by the keyword len, gives the length
	      of the packet.

	      For example, `ether[0] & 1 != 0' catches all multicast  traffic.
	      The  expression  `ip[0]  & 0xf != 5' catches all IP packets with
	      options. The expression `ip[6:2] &  0x1fff  =  0'	 catches  only
	      unfragmented  datagrams  and  frag zero of fragmented datagrams.
	      This check is implicitly applied to the tcp and udp index opera‐
	      tions.   For instance, tcp[0] always means the first byte of the
	      TCP header, and never means the first  byte  of  an  intervening
	      fragment.

       Primitives may be combined using:

	      A	 parenthesized	group of primitives and operators (parentheses
	      are special to the Shell and must be escaped).

	      Negation (`!' or `not').

	      Concatenation (`&&' or `and').

	      Alternation (`||' or `or').

       Negation has highest precedence.	 Alternation  and  concatenation  have
       equal  precedence  and associate left to right.	Note that explicit and
       tokens, not juxtaposition, are now required for concatenation.

       If an identifier is given without a keyword, the most recent keyword is
       assumed.	 For example,
	    not host vs and ace
       is short for
	    not host vs and host ace
       which should not be confused with
	    not ( host vs or ace )

       Expression arguments can be passed to ngrep as either a single argument
       or as multiple arguments, whichever is more convenient.	Generally,  if
       the  expression	contains Shell metacharacters, it is easier to pass it
       as a single, quoted argument.  Multiple arguments are concatenated with
       spaces before being parsed.

DIAGNOSTICS
       Errors from ngrep, libpcap, and the GNU regex library are all output to
       stderr.

EXIT STATUS
       The ngrep utility exits with one of the following values:

	    0	  One or more frames were matched.
	    1	  No frames were matched.
	    2	  An error occurred.
	    3+	  Hell is freezing over, run!

AUTHOR
       Written by Jordan Ritter <jpr5@darkridge.com>.

REPORTING BUGS
       Please report bugs to the ngrep's GitHub Issue Tracker, located at

	   http://github.com/jpr5/ngrep/issues

       Non-bug, non-feature-request general feedback should  be	 sent  to  the
       author directly by email.

NOTES
       ALL YOUR BASE ARE BELONG TO US.

*nux				September 2017			      NGREP(8)
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