V3/usr/man/man2/fstat.2

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NAME		fstat  --  get status of open file
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SYNOPSIS	(file descriptor in r0)
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sys fstat; buf  / fstat = 28.
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DESCRIPTION	This
call is identical to stat____, except that it operates
on open files instead of files given by name.
It is most often used to get the status
of the standard input and output files, whose names
are unknown.
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SEE ALSO	stat(II)
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DIAGNOSTICS	The error bit
(c-bit) is set if the file descriptor is unknown.
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BUGS		--