move-if-changed

#!/bin/sh
# Move file 1 to file 2 if they don't already match.
# Good for "make depend" for example, where it'd be nice to keep the
# old datestamp.
if [ $# != 2 ]; then
  echo 2>&1 usage: $0 newfile oldfilename
  exit 1
fi
#
if [ ! -r "$2" ]; then
  exec mv -f "$1" "$2"
fi
if cmp "$1" "$2" >/dev/null; then
  echo "$2 is unchanged"
  exec rm -f "$1"
fi
exec mv -f "$1" "$2"