=head1 NAME

chksum - Computes the file checksum of a file or files.

chksum [options] file1 {file2 file3 ...}

=head1 DESCRIPTION

I<chksum>  provides  most  of  the capabilities of the Unix I<sum> and I<cksum>
programs. It also implements the MD5 checksum based on the GNU MD5 code
implementation all in one package.

=head1 Usage

I<chksum>  command  can  be  used  to  compare  a  suspect file copied or
communicated over noisy transmission lines, internet or unpacked  from
an  archive  against  an exact copy of a trusted file.  The comparison
made by the command may not be cryptographically secure ; however,  it
is  unlikely  that  an accidentally damaged file will produce the same
checksum as the original file.

I<chksum>  was  initially written  to  offer  to  OpenVMS Users an exact
equivalent tool than what already exists (or  available  as  freeware)
under  Unix  system.  However, I<chksum> can be compiled on Unix system
and provides the same functionality across platform since the available
cksum and sum programs seems to give different results and their options
have different meaning.

=head1 Options

 -b     Computes the BSD checksum, computation with BUFSIZ blocks
 -r	Computes the BSD checksum, computation with 1Kb blocks
 -s	512-byte blocks SYSV compatible
 -o	1Kb blocks SYSV compatible
 -c	Cyclic Redundancy Check (CRC) checksum and number of bytes
	(according to IEEE Std 1003.2-1992 and X/Open CAE)
 -m	Compute MD5 checksum of files according to the definition
	of MD5 in RFC 1321 from April 1992.

Default is C<-b> unless overwritten by the environment variable CHKSUM_OPTION.
This variable should be set to one of "b","r","s","o","c" or "m".

=head1 Equivalences

 VMS/Unix	Digital Unix	Linux
 ------------------------------------------------
 $ chksum -r 	% sum -r	% sum -r
 $ chksum -o	% sum -o	% sum --sysv
 $ chksum -c	see below       % cksum

There are differences between the natice Digital Unix I<cksum> program
and the GNU I<cksum> program. I<chksum> is compatible with the GNU version
of I<cksum>.

=head1 Limitations

The default option is non-portable (depends on your OS BUFSIZ). It has
been preserved for backward compatibility purposes only. To change the
default option, define the environment variable CHKSUM_OPTION as described
in the C<Options> section.

Currently,  only  the  last version of a file can be checksum-ed under
VMS OS.

=head1 ReturnValue

I<chksum>  returns  a EXIT_SUCCESS status if no error was found, each +10
correspond to one file open/close error and +1 for each read-error.

=head1 VMSNotes

Return value

=over 4

This  return  value  will  produce  a  VMS  cli message which
relevance is doubtful AND misleading.  We maintained the  initial  scheme
for  cross-platform  portability  reasons i.e.  regardless of where you are
running chksum, the value returned to the shell  can  be  tested  within  a
script.

=back

Caveat

=over 4

How  did  I  test this program and what are the caveat ? Well, first,
I have tested on both Digital Unix and Linux for consistent results.

Then, I went  to  the  Seti homepage at 
C<http://setiathome.ssl.berkeley.edu/>  and  looked  at the different
checksum given in C<http://setiathome.ssl.berkeley.edu/unix.html> for
alpha_openvms_bck.exe downloaded on a Digital Unix machine. I could
reproduce the checksums given there using  C<-m>,  C<-r>  and C<-c>
options.

The  preceding  test failed when the same package was downloaded under
an OpenVMS node.  U<Don't panic> ! This is normal as explained below.

This   missmatch   comes   from   the  VMS  RMS  file  attributes  and
specifically, the missmatch between the 2 OS produced 'Record Format'.

 OSF1 downloaded file : Stream_LF, maximum 0 bytes, longest 0 bytes
 VMS downloaded file  : Fixed length 512 byte records

For  a fair comparison, you MUST convert your file to Stream_LF format
before using I<chksum>.  This can be done by using  (OpenVMS  6.2  and
above) the following command :

 $ set file/attribute=RFM:STMLF file.ext

=back

=head1 Version&Author

This help describes version 1.2* .

=over 4

The  CRC  code has been taken from cksum written by Q.  Frank Xia, and
Copyright (C) 92, 1995-1999 Free Software Foundation, Inc.

The  MD5  checksum has been implemented based on the routines provided
in the GNU version of MD5.C, written by Written by Ulrich Drepper  and
Copyright (C) 1995, 1996 Free Software Foundation, Inc.

=back

This software was otherwise written by Jerome LAURET
Copyright (c) 1999-2001 under the terms of the GNU GPL.

If  you encounter any problem with this utility (other than IO error),
please, send me an Email along with a description of what you did  and
the    file    you    tried    to    check.     Also,   please,   send
comments/suggestions/flame/blame/curses to me.  They are all  welcomed
and will help other people in future by making this software better.

Email : C<jlauret@mail.chem.sunysb.edu>

=cut