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NAMEread - read from a file descriptor
#include <unistd.h> ssize_t read(int fd, void *buf, size_t count);
DESCRIPTIONread() attempts to read up to count bytes from file descriptor fd into the buffer starting at buf.
If count is zero, fBread()fP returns zero and has no other results. If count is greater than SSIZE_MAX, the result is unspecified.
RETURN VALUEOn 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 errno is set appropriately. In this case it is left unspecified whether the file position (if any) changes.
Other errors may occur, depending on the object connected to fd. POSIX allows a read that is interrupted after reading some data to return -1 (with errno set to EINTR) or to return the number of bytes already read.
CONFORMING TOSVr4, SVID, AT&T, POSIX, X/OPEN, BSD 4.3
RESTRICTIONSOn NFS file systems, reading small amounts of data will only update the time stamp the first time, subsequent calls may not do so. This is caused by client side attribute caching, because most if not all NFS clients leave atime updates to the server and client side reads satisfied from the client's cache will not cause atime updates on the server as there are no server side reads. UNIX semantics can be obtained by disabling client side attribute caching, but in most situations this will substantially increase server load and decrease performance.
SEE ALSOclose(2), fcntl(2), ioctl(2), lseek(2), readdir(2), readlink(2), select(2), write(2), fread(3), readv(3)