Programming Perl, 4th Edition

syswrite

syswrite FILEHANDLE, SCALAR, LENGTH, OFFSET
syswrite FILEHANDLE, SCALAR, LENGTH
syswrite FILEHANDLE, SCALAR

This function tries to write LENGTH bytes of data from variable SCALAR to the specified FILEHANDLE using the write(2) syscall. The function returns the number of bytes written, or undef on error. The OFFSET, if specified, says from where in the string to start writing. (You might do this if you were using the string as a buffer, for instance, or if you needed to recover from a partial write.) A negative OFFSET specifies that writing should start that many bytes backward from the end of the string. If SCALAR is empty, the only OFFSET permitted is 0. An exception is raised if LENGTH is negative or if OFFSET points outside the string.

To copy data from filehandle FROM into filehandle TO, you can use something like:

use Errno qw/EINTR/; $blksize = (stat FROM)[11] || 16384; # preferred block size? while ($len = sysread FROM, $buf, $blksize) { if (!defined $len) { next if $! == EINTR; die "System read error: $!"; } $offset = 0; while ($len) { # Handle partial writes $written ...