sum (Unix)
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| sum | |
|---|---|
| [[Programmer|Original authorTemplate:Pluralize from text]] | Ken Thompson |
| [[Programmer|DeveloperTemplate:Pluralize from text]] | AT&T Bell Laboratories |
| Initial release | November 3, 1971 |
| Operating system | Unix, Unix-like, Inferno |
| Platform | Cross-platform |
| Type | Command |
| License | coreutils: GPLv3+ |
| Website | Script error: No such module "WikidataIB". |
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Page Template:Mono/styles.css has no content.sum is a legacy utility available on some Unix and Unix-like operating systems. This utility outputs a 16-bit checksum of each argument file, as well as the number of blocks they take on disk.[1] Two different checksum algorithms are in use. POSIX abandoned sum in favor of cksum.
Overview
The Page Template:Mono/styles.css has no content.sum program is generally only useful for historical interest. It is not part of POSIX. Two algorithms are typically available: a BSD checksum and a SYSV checksum. Both are weaker than the already weak 32-bit CRC used by cksum.[2]
The default algorithm on FreeBSD and GNU implementations is the BSD checksum. Switching between the two algorithms is done via command line options.[2][1]
The two commonly used algorithms are as follows.
The BSD sum, -r in GNU sum and -o1 in FreeBSD cksum:
- Initialize checksum to 0
- For each byte of the input stream
- Perform 16-bit bitwise right rotation by 1 bit on the checksum
- Add the byte to the checksum, and apply modulo 2 ^ 16 to the result, thereby keeping it within 16 bits
- The result is a 16-bit checksum
The above algorithm appeared in Seventh Edition Unix.
The System V sum, -s in GNU sum and -o2 in FreeBSD cksum:
- checksum0 = sum of all bytes of the input stream modulo 2 ^ 32
- checksum1 = checksum0 modulo 2 ^ 16 + checksum0 / 2 ^ 16
- checksum = checksum1 modulo 2 ^16 + checksum1 / 2 ^ 16
- The result is a 16-bit checksum calculated from the initial 32-bit plain byte sum
Syntax
The Page Template:Mono/styles.css has no content.sum utility is invoked from the command line according to the following syntax:
sum [OPTION]... [FILE]...
with the possible option parameters being:
- Page Template:Mono/styles.css has no content.-r
- use BSD checksum algorithm, use 1K blocks (defeats Page Template:Mono/styles.css has no content.-s)
- Page Template:Mono/styles.css has no content.-s, Page Template:Mono/styles.css has no content.--sysv
- use SYSV checksum algorithm, use 512 bytes blocks
- Page Template:Mono/styles.css has no content.--help
- display the help screen and exit
- Page Template:Mono/styles.css has no content.--version
- output version information and exit
When no file parameter is given, or when FILE is Page Template:Mono/styles.css has no content.-, the standard input is used as input file.
Example of use:
$ echo Hello > testfile
$ sum testfile
36978 1
Example of -s use in GNU sum:
$ echo Hello > testfile
$ sum -s testfile
510 1 testfile
Example of using standard input, -r and printf to avoid newline:
$ printf Hello | sum -r
08401 1
See also
- GNU Core Utilities
- UnxUtils port to native Win32
References
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- ^ a b Template:Man/format — manual pages from GNU coreutils
- ^ a b Template:Man
External links
- sum in The Single UNIX ® Specification, Version 2, 1997, opengroup.org – does not specify checksum algorithm
- C.4 Utilities in The Open Group Base Specifications Issue 7, 2018 edition, opengroup.org – indicates sum as removed
- Template:Man
- Template:Man/format – manual pages from GNU coreutils
- Template:Man – states the sum algorithms in options -o1 and -o2 to cksum
- Template:Man
- Template:Man
- The Unix Tree, tuhs.org – the source code of old versions of Unix
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