Attempts to write LENGTH bytes of data from variable SCALAR to the
specified FILEHANDLE, using the system call write(2). If LENGTH is
not specified, writes whole SCALAR. It bypasses buffered IO, so
mixing this with reads (other than sysread()), print, write,
seek, tell, or eof may cause confusion because the perlio and
stdio layers usually buffers data. Returns the number of bytes
actually written, or undef if there was an error (in this case the
errno variable $! is also set). If the LENGTH is greater than the
available data in the SCALAR after the OFFSET, only as much data as is
available will be written.
An OFFSET may be specified to write the data from some part of the string other than the beginning. A negative OFFSET specifies writing that many characters counting backwards from the end of the string. In the case the SCALAR is empty you can use OFFSET but only zero offset.
Note that if the filehandle has been marked as :utf8, Unicode
characters are written instead of bytes (the LENGTH, OFFSET, and the
return value of syswrite() are in UTF-8 encoded Unicode characters).
The :encoding(...) layer implicitly introduces the :utf8 layer.
See /binmode, /open, and the open pragma, open.