V3/man/man1/sum.1

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NAME		sum  --  sum file
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SYNOPSIS	sum___ name\d1\u ...
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DESCRIPTION	sum___
sums the contents of the bytes (mod 2^16) of
one or more files and prints the answer in octal.
A separate sum is printed for each file specified,
along with the number of whole or partial
512-byte blocks read.

In practice, sum___ is often used to verify that
all of a special file can be read without error.
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FILES		none
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SEE ALSO	--
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DIAGNOSTICS	"oprd" if the file cannot be
opened; "?" if an error is discovered during the read.
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BUGS		none