editcap - Edit and/or translate the format of capture files
editcap [ -c <packets per file> ] [ -C <choplen> ]
[ -E <error probability> ] [ -F <file format> ] [ -A <start time> ]
[ -B <stop time> ] [ -h ] [ -i <seconds per file> ] [ -r ]
[ -s <snaplen> ] [ -t <time adjustment> ] [ -T <encapsulation type> ]
[ -v ] infile outfile [ packet#[-packet#] ... ]
editcap -d | -D <dup window> | -w <dup time window> [ -v ] infile
Editcap is a program that reads some or all of the captured packets
from the infile, optionally converts them in various ways and writes
the resulting packets to the capture outfile (or outfiles).
By default, it reads all packets from the infile and writes them to the
outfile in libpcap file format.
An optional list of packet numbers can be specified on the command
tail; individual packet numbers separated by whitespace and/or ranges
of packet numbers can be specified as start-end, referring to all
packets from start to end. By default the selected packets with those
numbers will not be written to the capture file. If the -r flag is
specified, the whole packet selection is reversed; in that case only
the selected packets will be written to the capture file.
Editcap can also be used to remove duplicate packets. Several
different options (-d, -D and -w) are used to control the packet window
or relative time window to be used for duplicate comparison.
Editcap is able to detect, read and write the same capture files that
are supported by Wireshark. The input file doesn't need a specific
filename extension; the file format and an optional gzip compression
will be automatically detected. Near the beginning of the DESCRIPTION
section of wireshark(1) or
<http://www.wireshark.org/docs/man-pages/wireshark.html> is a detailed
description of the way Wireshark handles this, which is the same way
Editcap handles this.
Editcap can write the file in several output formats. The -F flag can
be used to specify the format in which to write the capture file;
editcap -F provides a list of the available output formats.
-c <packets per file>
Splits the packet output to different files based on uniform packet
counts with a maximum of <packets per file> each. Each output file
will be created with a suffix -nnnnn, starting with 00000. If the
specified number of packets is written to the output file, the next
output file is opened. The default is to use a single output file.
Sets the chop length to use when writing the packet data. Each
packet is chopped at the packet end by a few <choplen> bytes of
This is useful in the rare case that the conversion between two
file formats leaves some random bytes at the end of each packet.
-d Attempts to remove duplicate packets. The length and MD5 hash of
the current packet are compared to the previous four (4) packets.
If a match is found, the current packet is skipped. This option is
equivalent to using the option -D 5.
-D <dup window>
Attempts to remove duplicate packets. The length and MD5 hash of
the current packet are compared to the previous <dup window> - 1
packets. If a match is found, the current packet is skipped.
The use of the option -D 0 combined with the -v option is useful in
that each packet's Packet number, Len and MD5 Hash will be printed
to standard out. This verbose output (specifically the MD5 hash
strings) can be useful in scripts to identify duplicate packets
across trace files.
The <dup window> is specifed as an integer value between 0 and
NOTE: Specifying large <dup window> values with large tracefiles
can result in very long processing times for editcap.
-w <dup time window>
Attempts to remove duplicate packets. The current packet's arrival
time is compared with up to 1000000 previous packets. If the
packet's relative arrival time is less than or equal to the <dup
time window> of a previous packet and the packet length and MD5
hash of the current packet are the same then the packet to skipped.
The duplicate comparison test stops when the current packet's
relative arrival time is greater than <dup time window>.
The <dup time window> is specifed as seconds[.fractional seconds].
The [.fractional seconds] component can be specified to nine (9)
decimal places (billionths of a second) but most typical trace
files have resolution to six (6) decimal places (millionths of a
NOTE: Specifying large <dup time window> values with large
tracefiles can result in very long processing times for editcap.
NOTE: The -w option assumes that the packets are in chronological
order. If the packets are NOT in chronological order then the -w
duplication removal option may not identify some duplicates.
-E <error probability>
Sets the probabilty that bytes in the output file are randomly
changed. Editcap uses that probability (between 0.0 and 1.0
inclusive) to apply errors to each data byte in the file. For
instance, a probability of 0.02 means that each byte has a 2%
chance of having an error.
This option is meant to be used for fuzz-testing protocol
-F <file format>
Sets the file format of the output capture file. Editcap can write
the file in several formats, editcap -F provides a list of the
available output formats. The default is the libpcap format.
-A <start time>
Saves only the packets whose timestamp is on or after start time.
The time is given in the following format YYYY-MM-DD HH:MM:SS
-B <stop time>
Saves only the packets whose timestamp is on or before stop time.
The time is given in the following format YYYY-MM-DD HH:MM:SS
-h Prints the version and options and exits.
-i <seconds per file>
Splits the packet output to different files based on uniform time
intervals using a maximum interval of <seconds per file> each. Each
output file will be created with a suffix -nnnnn, starting with
00000. If packets for the specified time interval are written to
the output file, the next output file is opened. The default is to
use a single output file.
-r Reverse the packet selection. Causes the packets whose packet
numbers are specified on the command line to be written to the
output capture file, instead of discarding them.
Sets the snapshot length to use when writing the data. If the -s
flag is used to specify a snapshot length, packets in the input
file with more captured data than the specified snapshot length
will have only the amount of data specified by the snapshot length
written to the output file.
This may be useful if the program that is to read the output file
cannot handle packets larger than a certain size (for example, the
versions of snoop in Solaris 2.5.1 and Solaris 2.6 appear to reject
Ethernet packets larger than the standard Ethernet MTU, making them
incapable of handling gigabit Ethernet captures if jumbo packets
-t <time adjustment>
Sets the time adjustment to use on selected packets. If the -t
flag is used to specify a time adjustment, the specified adjustment
will be applied to all selected packets in the capture file. The
adjustment is specified as [-]seconds[.fractional seconds]. For
example, -t 3600 advances the timestamp on selected packets by one
hour while -t -0.5 reduces the timestamp on selected packets by
This feature is useful when synchronizing dumps collected on
different machines where the time difference between the two
machines is known or can be estimated.
-T <encapsulation type>
Sets the packet encapsulation type of the output capture file. If
the -T flag is used to specify an encapsulation type, the
encapsulation type of the output capture file will be forced to the
specified type. editcap -T provides a list of the available types.
The default type is the one appropriate to the encapsulation type
of the input capture file.
Note: this merely forces the encapsulation type of the output file
to be the specified type; the packet headers of the packets will
not be translated from the encapsulation type of the input capture
file to the specified encapsulation type (for example, it will not
translate an Ethernet capture to an FDDI capture if an Ethernet
capture is read and '-T fddi' is specified). If you need to
remove/add headers from/to a packet, you will need
-v Causes editcap to print verbose messages while it's working.
Use of -v with the de-duplication switches of -d, -D or -w will
cause all MD5 hashes to be printed whether the packet is skipped or
To see more detailed description of the options use:
To shrink the capture file by truncating the packets at 64 bytes and
writing it as Sun snoop file use:
editcap -s 64 -F snoop capture.pcap shortcapture.snoop
To delete packet 1000 from the capture file use:
editcap capture.pcap sans1000.pcap 1000
To limit a capture file to packets from number 200 to 750 (inclusive)
editcap -r capture.pcap small.pcap 200-750
To get all packets from number 1-500 (inclusive) use:
editcap -r capture.pcap first500.pcap 1-500
editcap capture.pcap first500.pcap 501-9999999
To exclude packets 1, 5, 10 to 20 and 30 to 40 from the new file use:
editcap capture.pcap exclude.pcap 1 5 10-20 30-40
To select just packets 1, 5, 10 to 20 and 30 to 40 for the new file
editcap -r capture.pcap select.pcap 1 5 10-20 30-40
To remove duplicate packets seen within the prior four frames use:
editcap -d capture.pcap dedup.pcap
To remove duplicate packets seen within the prior 100 frames use:
editcap -D 101 capture.pcap dedup.pcap
To remove duplicate packets seen equal to or less than 1/10th of a
editcap -w 0.1 capture.pcap dedup.pcap
To display the MD5 hash for all of the packets (and NOT generate any
real output file):
editcap -v -D 0 capture.pcap /dev/null
or on Windows systems
editcap -v -D 0 capture.pcap NUL
To introduce 5% random errors in a capture file use:
editcap -E 0.05 capture.pcap capture_error.pcap
tcpdump(8), pcap(3), wireshark(1), tshark(1), mergecap(1), dumpcap(1),
capinfos(1), text2pcap(1), od(1)
Editcap is part of the Wireshark distribution. The latest version of
Wireshark can be found at <http://www.wireshark.org>.
HTML versions of the Wireshark project man pages are available at:
Richard Sharpe <sharpe[AT]ns.aus.com>
Guy Harris <guy[AT]alum.mit.edu>
Ulf Lamping <ulf.lamping[AT]web.de>