move-if-change

#!/bin/sh
# Like mv $1 $2, but if the files are the same, just delete $1.
# Status is zero if successful, nonzero otherwise.

usage="$0: usage: $0 SOURCE DEST"

case $# in
2) ;;
*) echo "$usage" >&2; exit 1;;
esac

for arg in "$1" "$2"; do
  case $arg in
   -*) echo "$usage" >&2; exit 1;;
  esac
done

if test -r "$2" && cmp -s "$1" "$2"; then
  rm -f "$1"
else
  mv -f "$1" "$2"
fi