#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11157093
use warnings;
$| = 1; # NOTE

# slightly reformatted from your code - $sock not needed

while( my $cmd = <> )
  {
  if( $cmd =~ m/^sleep (\d+)/ )
    {
    my $snooze_time = $1;
    printf "Will sleep for $snooze_time seconds\n";
    sleep $snooze_time;
    print "... ZZZ ... Yawn ... What next oh master?\n";
    }
# NB: In real life there are lots of other commands and many take some time to process.
  else
    {
    print "I did not understand that. What next oh master?\n";
    }
  }

__END__

#
# unlisted service
# (goes in /etc/xinetd.d) NOTE change user, server, and only_from
# if this file changed, use 'systemctl reload xinetd' so prev still run
# using 'restart' will kill running servers, 'reload' will not
#

service unlisted-pm11157093
{
  type                = UNLISTED
  socket_type         = stream
  protocol            = tcp
  wait                = no
  user                = rick
  log_type            = FILE /dev/null
  server              = /home/rick/code/pm11157093.pl
  port                = 1234
  disable             = no
  only_from           = 127.0.0.1 192.168.1.0/24
}