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Full Discussion: cksum parts of a file
Top Forums UNIX for Dummies Questions & Answers cksum parts of a file Post 25441 by auswipe on Tuesday 30th of July 2002 11:38:27 AM
Old 07-30-2002
I would write a routine in C (or C++) that would open the source files and then fseek offsets from 0 to (n-1) (where n is the length of the file) and just skip over or substitute a common character (say, captial X) for bytes 223 and 224 and write it out to a temporary binary file and run checksum against it and then perform the same with the second file and then compare checksums.

You could probably also write a similiar routine in perl as well but C seems to appropriate.
 

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cksum(1)						      General Commands Manual							  cksum(1)

NAME
cksum - print file checksum and sizes SYNOPSIS
[file ...] DESCRIPTION
The command calculates and prints to standard output a checksum for each named file, the number of octets in the file and the filename. uses a portable algorithm based on a 32-bit Cyclic Redundancy Check. This algorithm finds a broader spectrum of errors than the 16-bit algorithms used by (see sum(1)). The CRC is the sum of the following expressions, where x is each byte of the file. + x^8 + x^7 + x^5 + x^4 + x^2 + x^1 + x^0 x26 + x23 + x22 + x16 + x12 + x11 + x10 + x7 + x5 + x4 + x2 + x1 + x0 The results of the calculation are truncated to a 32-bit value. The number of bytes in the file is also printed. Standard input is used if no file names are given. is typically used to verify data integrity when copying files between systems. EXTERNAL INFLUENCES
Environment Variables determines the locale to use for the locale categories when both and the corresponding environment variable (beginning with do not specify a locale. If is not set or is set to the empty string, a default of "C" (see lang(5)) is used. determines the locale for interpretation of sequences of bytes of text data as characters (e.g., single- verses multibyte characters in arguments and input files). determines the language in which messages are displayed. If any internationalization variable contains an invalid setting, behaves as if all internationalization variables are set to "C". See environ(5). RETURN VALUE
Upon completion, returns one of the following values: All files were processed successfully. One or more files could not be read or another error occurred. If an inaccessible file is encountered, continues processing any remaining files, but the final exit status is affected. SEE ALSO
sum(1), wc(1). STANDARDS CONFORMANCE
cksum(1)
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