tool/ifchange

   1 #!/bin/sh
   2 # usage: ifchange target temporary
   3
   4 target="$1"
   5 temp="$2"
   6 if [ "$temp" = - ]; then
   7     temp="tmpdata$$.tmp~"
   8     cat > "$temp" || exit $?
   9     trap 'rm -f "$temp"' 0
  10 fi
  11 if cmp "$target" "$temp" >/dev/null 2>&1; then
  12     echo "$target unchanged"
  13     rm -f "$temp"
  14 else
  15     echo "$target updated"
  16     mv -f "$temp" "$target"
  17 fi