.\" Hey Emacs! This file is -*- nroff -*- source. .\" .\" This manpage is Copyright (C) 1992 Drew Eckhardt; .\" 1993 Michael Haardt, Ian Jackson. .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" Modified Sat Jul 24 00:06:00 1993 by Rik Faith (faith@cs.unc.edu) .\" Modified Wed Jan 17 16:02:32 1996 by Michael Haardt .\" (michael@cantor.informatik.rwth-aachen.de) .\" Modified Thu Apr 11 19:26:35 1996 by Andries Brouwer (aeb@cwi.nl) .\" Modified Sun Jul 21 18:59:33 1996 by Andries Brouwer (aeb@cwi.nl) .\" .TH READ 2 "17 Januari 1996" Linux "Linux Programmer's Manual" .SH NAME read \- read from a file descriptor .SH SYNOPSIS .nf .B #include .sp .BI "ssize_t read(int " fd ", void *" buf ", size_t " count ); .fi .SH DESCRIPTION .B read() attempts to read up to .I count bytes from file descriptor .I fd into the buffer starting at .IR buf . .PP If .I count is zero, \fBread()\fP returns zero and has no other results. If .I count is greater than SSIZE_MAX, the result is unspecified. .PP .SH "RETURN VALUE" On success, the number of bytes read is returned (zero indicates end of file), and the file position is advanced by this number. It is not an error if this number is smaller than the number of bytes requested; this may happen for example because fewer bytes are actually available right now (maybe because we were close to end-of-file, or because we are reading from a pipe, or from a terminal), or because \fBread()\fP was interrupted by a signal. On error, \-1 is returned, and .I errno is set appropriately. In this case it is left unspecified whether the file position (if any) changes. .SH ERRORS .TP 0.8i .B EINTR The call was interrupted by a signal before any data was read. .TP .B EAGAIN Non-blocking I/O has been selected using .B O_NONBLOCK and no data was immediately available for reading. .TP .B EIO I/O error. This will happen for example when the process is in a background process group, tries to read from its controlling tty, and either it is ignoring or blocking SIGTTIN or its process group is orphaned. .TP .B EISDIR .I fd refers to a directory. .TP .B EBADF .I fd is not a valid file descriptor or is not open for reading. .TP .B EINVAL .I fd is attached to an object which is unsuitable for reading. .TP .B EFAULT .I buf is outside your accessible address space. .PP Other errors may occur, depending on the object connected to .IR fd . POSIX allows a .B read that is interrupted after reading some data to return \-1 (with .I errno set to EINTR) or to return the number of bytes already read. .SH "CONFORMING TO" SVID, AT&T, POSIX, X/OPEN, BSD 4.3 .SH "SEE ALSO" .BR readdir "(2), " write "(2), " write "(2), " fcntl "(2), " close "(2), " .BR lseek "(2), " .BR select "(2), " readlink "(2), " ioctl "(2), " fread (3).