read - read from a file descriptor
#include <unistd.h>
ssize_t read(int fd, void buf[.count], size_t count);read() attempts to read up to count bytes
from file descriptor fd into the buffer starting at
buf.
On files that support seeking, the read operation commences at the file offset, and the file offset is incremented by the number of bytes read. If the file offset is at or past the end of file, no bytes are read, and read() returns zero.
If count is zero, read() may
detect the errors described below. In the absence of any errors, or if
read() does not check for errors, a
read() with a count of 0 returns zero and has
no other effects.
According to POSIX.1, if count is greater than
SSIZE_MAX, the result is implementation-defined; see
NOTES for the upper limit on Linux.
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 read() was interrupted by a signal. See also NOTES.
On error, -1 is returned, and errno is set to indicate the
error. In this case, it is left unspecified whether the file position
(if any) changes.