Attempts to read LENGTH characters of data into variable SCALAR from the
specified FILEHANDLE, using the system call read(2). It bypasses buffered IO, so mixing
this with other kinds of reads, print, write, seek,
tell, or eof can cause confusion because stdio usually buffers
data. Returns the number of characters actually read, 0 at end of file, or
undef if there was an error. SCALAR will be grown or shrunk so that the last byte actually
read is the last byte of the scalar after the read.
Note the characters: depending on the status of the filehandle, either (8-bit)
bytes or characters are read. By default all filehandles operate on bytes, but for example
if the filehandle has been opened with the :utf8 I/O layer (see /open, and the open
pragma, open), the I/O will
operate on characters, not bytes.
An OFFSET may be specified to place the read data at some place in the string other
than the beginning. A negative OFFSET specifies placement at that many characters counting
backwards from the end of the string. A positive OFFSET greater than the length of SCALAR
results in the string being padded to the required size with "\0"
bytes before the result of the read is appended.
There is no syseof() function, which is ok, since eof() doesn't work very well on
device files (like ttys) anyway. Use sysread() and check for a return value for 0 to
decide whether you're done.
