> Are you using read, readline (aka <>) or eof? Those aren't compatible with select. You need to use sysread.

Good point. Reminded me of this old node, an example of a complete event-driven Perl server using IO::Select. From its source code:

# -----------------------------------------------------------------
# Perl network programming notes
# ------------------------------
# Reading can be done with:
#  1) <$sock> - blocks till new line
#  2) read($sock, $buf, $len) - blocks till $len bytes received
#                               (like W Richard Stevens readn function
+ in C)
#  3) sysread($sock, $buf, $len) - may return less than asked for
#                                  (like read()/recv() in C)
# -------------------------------------------------------
...

   # This one blocks until newline received.
   # $data = <$client>;

   #  This one blocks till $len bytes received (like Stevens readn fun
+ction in C)
   # my $hdr;
   # my $hdrlen = read( $client, $hdr, $SYSLOG_HDR_LEN );

   # This one may return less than asked for (like read()/recv() in C)
   my $msglen = sysread( $client, $data, $SYSLOG_MAX_MSG_LEN );
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Given the commenting out above, I presumably tried all three at the time before settling on sysread. :)