V10/man/man2/read.2

.TH READ 2
.CT 2 file_io comm_proc
.SH NAME
read, write \(mi read or write file
.SH SYNOPSIS
.nf
.B int read(fildes, buffer, nbytes)
.B char *buffer;
.PP
.B int write(fildes, buffer, nbytes)
.B char *buffer;
.fi
.SH DESCRIPTION
.I Read
reads
.I nbytes
bytes of data
from the file pointer location in the file associated with
.I fildes
into memory at
.IR buffer .
The file pointer is advanced by the number of bytes read.
It is not guaranteed
that all
.I nbytes
bytes will be read; for example
if the file refers to a terminal at most one line
will be returned.
In any event the number of characters read is returned.
A return value of
0 is conventionally interpreted as end of file.
.PP
.I Write
writes
.I nbytes
bytes of data starting at
.I buffer
to the file associated with
.I fildes
at the file pointer location.
The file pointer is advanced by the number of bytes written.
The number of characters actually written is returned.
It should be regarded as an error
if this is not the same as requested.
.PP
Reads and writes which are aligned with file system blocks
are more efficient than others; see
.IR filsys (5).
.SH "SEE ALSO"
.IR open (2), 
.IR dup (2),
.IR pipe (2),
.IR select (2),
.IR dirread (2)
.SH DIAGNOSTICS
.IR read :
.BR EBADF ,
.BR EFAULT ,
.BR EINTR ,
.BR EINVAL ,
.BR ENXIO
.br
.IR write :
.BR EBADF ,
.BR EFAULT ,
.BR EINTR ,
.BR EINVAL ,
.BR EIO ,
.BR ENXIO ,
.BR EPIPE ,
.BR EROFS
.SH BUGS
A
.I read
or a
.I write
call may fail because of a prior call to
.IR lseek (2).