If program blah really wants input on STDIN then it may be instructive for you to change your $command to "/bin/cat".

OTOH, if blah actually wants those strings on the command line you need to make a change:

$UPDATE = `$command << EOF`;
$variable is the value from DB. 
$variable is less that $threshold
EOF
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In this case you would test by changing $command to "/bin/echo".