This is the code I'm using. It reproduces the same results as zip's CRC32.
(try zipping a small file and then unzip -v file on the cmdline). The poly is the same as the one mentioned in the cksum man page.
methyl thanks for the link, it has some pseudo code new to me. I'll try to find the Sarwate article about table generation, maybe it will cast some light on what is done different in cksum.
hi,
I am trying to use the cksum feature in unix. when i make a call to it i get returned something along the lines of:
4603435 14 file3
how do i get the first part of this response only; i.e:
4603435
I'm trying to use at a way without the use of sed and creating temp... (4 Replies)
Hello,
I am trying to return the name of the resulting file from a .zip archive file using unix unzip command.
unzip c07212007.cef7081.zip
Archive: c07212007.cef7081.zip
SecureZIP for z/OS by PKWARE
inflating: CEP/CEM7080/PPVBILL/PASS/G0063V00
I used the following command to unzip in... (5 Replies)
I have to zip many pdf files and the size of zip file must not exceed 200 MB. When size is more than 200 MB then multiple zip files needs to be created.
How we can achieve this in UNIX?
I have tried ZIP utility but it takes a lot of time when we add individual pdfs by looping through a... (1 Reply)
Is cksum the right command to calculate the crc32 checksum value? I tried it for a number of files now and every time the results dont match. So there is nothing wrong with the file. Also, cksum gives me an all numerical value while crc32 is alpha numeric. What am I doing wrong?
Thanks (9 Replies)
I would like to list all files in a directory tree but with a prepended digest hash code (like CRC32). CRC32 is not a MUST. If suitable another hash code can be used as well. In case of CRC32 the listing should look like
3765AC \usr\bin\spool
23CE99 \usr\bin\spool\list.h
...
11AA04... (3 Replies)
Hi
I have a requirement in unix shell where I need to zip multiple files on server to one single .zip file. I dont see zip command in AIX and gzip command not doing completely what I want.
One I do .zip file, I should be able to unzip in my local Computer.
Here is example what I want... (9 Replies)
Hi all i am very new to shell scripting and need some help from you to learn
1)i have some log files that gets generated on daily basis example: i have abc_2017_01_30_1.log ,2017_01_30_2.log like wise so i want to zip this 4 logs which are created on same date into one zip folder.
2)Post zipping... (2 Replies)
Hi all i am very new to shell scripting and need some help from you to learn
1)i have some log files that gets generated on daily basis example: i have abc_2017_01_30_1.log ,2017_01_30_2.log like wise so i want to zip this 4 logs which are created on same date into one zip folder.
2)Post zipping... (1 Reply)
Discussion started by: b.saipriyanka
1 Replies
LEARN ABOUT OSX
cksum
CKSUM(1) BSD General Commands Manual CKSUM(1)NAME
cksum, sum -- display file checksums and block counts
SYNOPSIS
cksum [-o 1 | 2 | 3] [file ...]
sum [file ...]
DESCRIPTION
The cksum utility writes to the standard output three whitespace separated fields for each input file. These fields are a checksum CRC, the
total number of octets in the file and the file name. If no file name is specified, the standard input is used and no file name is written.
The sum utility is identical to the cksum utility, except that it defaults to using historic algorithm 1, as described below. It is provided
for compatibility only.
The options are as follows:
-o Use historic algorithms instead of the (superior) default one.
Algorithm 1 is the algorithm used by historic BSD systems as the sum(1) algorithm and by historic AT&T System V UNIX systems as the
sum(1) algorithm when using the -r option. This is a 16-bit checksum, with a right rotation before each addition; overflow is dis-
carded.
Algorithm 2 is the algorithm used by historic AT&T System V UNIX systems as the default sum(1) algorithm. This is a 32-bit checksum,
and is defined as follows:
s = sum of all bytes;
r = s % 2^16 + (s % 2^32) / 2^16;
cksum = (r % 2^16) + r / 2^16;
Algorithm 3 is what is commonly called the '32bit CRC' algorithm. This is a 32-bit checksum.
Both algorithm 1 and 2 write to the standard output the same fields as the default algorithm except that the size of the file in
bytes is replaced with the size of the file in blocks. For historic reasons, the block size is 1024 for algorithm 1 and 512 for
algorithm 2. Partial blocks are rounded up.
The default CRC used is based on the polynomial used for CRC error checking in the networking standard ISO/IEC 8802-3:1989. The CRC checksum
encoding is defined by the generating polynomial:
G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
Mathematically, the CRC value corresponding to a given file is defined by the following procedure:
The n bits to be evaluated are considered to be the coefficients of a mod 2 polynomial M(x) of degree n-1. These n bits are the bits
from the file, with the most significant bit being the most significant bit of the first octet of the file and the last bit being the
least significant bit of the last octet, padded with zero bits (if necessary) to achieve an integral number of octets, followed by one
or more octets representing the length of the file as a binary value, least significant octet first. The smallest number of octets
capable of representing this integer are used.
M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by G(x) using mod 2 division, producing a remainder R(x) of degree
<= 31.
The coefficients of R(x) are considered to be a 32-bit sequence.
The bit sequence is complemented and the result is the CRC.
EXIT STATUS
The cksum and sum utilities exit 0 on success, and >0 if an error occurs.
SEE ALSO md5(1)
The default calculation is identical to that given in pseudo-code in the following ACM article.
Dilip V. Sarwate, "Computation of Cyclic Redundancy Checks Via Table Lookup", Communications of the ACM, August 1988.
STANDARDS
The cksum utility is expected to conform to IEEE Std 1003.2-1992 (``POSIX.2'').
HISTORY
The cksum utility appeared in 4.4BSD.
BSD April 28, 1995 BSD