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cksum - Man Page

Calculate a cksum(1) compatible checksum


package require Tcl  8.2

package require cksum  ?1.1.4?

::crc::cksum ?-format format? ?-chunksize size? [ -channel chan | -filename file | string ]


::crc::CksumUpdate token data

::crc::CksumFinal token


This package provides a Tcl implementation of the cksum(1) algorithm based upon information provided at in the GNU implementation of this program as part of the GNU Textutils 2.0 package.


::crc::cksum ?-format format? ?-chunksize size? [ -channel chan | -filename file | string ]

The command takes string data or a channel or file name and returns a checksum value calculated using the cksum(1) algorithm. The result is formatted using the format(n) specifier provided or as an unsigned integer (%u) by default.


-channel name

Return a checksum for the data read from a channel. The command will read data from the channel until the eof is true. If you need to be able to process events during this calculation see the Programming Interface section

-filename name

This is a convenience option that opens the specified file, sets the encoding to binary and then acts as if the -channel option had been used. The file is closed on completion.

-format string

Return the checksum using an alternative format template.

Programming Interface

The cksum package implements the checksum using a context variable to which additional data can be added at any time. This is expecially useful in an event based environment such as a Tk application or a web server package. Data to be checksummed may be handled incrementally during a fileevent handler in discrete chunks. This can improve the interactive nature of a GUI application and can help to avoid excessive memory consumption.


Begins a new cksum context. Returns a token ID that must be used for the remaining functions. An optional seed may be specified if required.

::crc::CksumUpdate token data

Add data to the checksum identified by token. Calling CksumUpdate $token "abcd" is equivalent to calling CksumUpdate $token "ab" followed by CksumUpdate $token "cb". See Examples.

::crc::CksumFinal token

Returns the checksum value and releases any resources held by this token. Once this command completes the token will be invalid. The result is a 32 bit integer value.


% crc::cksum "Hello, World!"
% crc::cksum -format 0x%X "Hello, World!"
% crc::cksum -file cksum.tcl
% set tok [crc::CksumInit]
% crc::CksumUpdate $tok "Hello, "
% crc::CksumUpdate $tok "World!"
% crc::CksumFinal $tok


Pat Thoyts

Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category crc of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

See Also

crc32(n), sum(n)


checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security


Hashes, checksums, and encryption

Referenced By

crc16(n), crc32(n), sum(n).

1.1.4 tcllib Cyclic Redundancy Checks