Print changes over time in program output

diffwatch

#!/bin/bash

out1=$(mktemp)
out2=$(mktemp)

$* > $out1

date -u --rfc-3339=ns
cat $out1
echo

while true; do
  sleep ${FREQ:-2}
  $* > $out2
  if ! diff -q $out1 $out2 > /dev/null; then
    date -u --rfc-3339=ns
    diff -u $out1 $out2
    echo
    mv $out2 $out1
  fi
done

TODO: clean up temp files