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Attempts to write LENGTH bytes of data from variable SCALAR to the specified FILEHANDLE, using 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 data available 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. If SCALAR is of length zero, you can only use an OFFSET of 0.

Warning: If the filehandle is marked :utf8, Unicode characters encoded in UTF-8 are written instead of bytes, and the LENGTH, OFFSET, and 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.