can_read() may be just telling you that you need to empty the pipe of data. Also, you may want to use sysread() instead of <...>. From the select perldocs...

   WARNING: One should not attempt to mix buffered I/O
   (like "read" or <FH>) with "select", except as
   permitted by POSIX, and even then only on POSIX
   systems.  You have to use "sysread" instead.
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