sysread - fixed-length unbuffered input from a filehandle
Attempts to read LENGTH bytes of data into variable SCALAR from the
specified FILEHANDLE, using the system call read(2). It bypasses
stdio, so mixing this with other kinds of reads may cause confusion.
Returns the number of bytes actually read, or undef if there was an
error. SCALAR will be grown or shrunk to the length actually read. An
OFFSET may be specified to place the read data at some other place than
the beginning of the string.