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 stdio, so mixing this with reads (other than
eof may cause confusion because stdio usually buffers data. Returns the number of bytes actually written, or
undef if there was an error. 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 bytes counting backwards from the end of the string. In the case the SCALAR is empty you can use OFFSET but only zero offset.