dev/refresh

   1 #!/usr/bin/env bash
   2
   3 set -ueo pipefail
   4
   5 # Related: https://joeyh.name/code/moreutils/ sponge
   6
   7 usage()
   8 {
   9     echo 'Usage: refresh [-a] [-v] DEST'
  10     echo '       refresh [-a] [-v] -- DEST'
  11 }
  12
  13 append=''
  14 verbose=''
  15
  16 while test $# -gt 0; do
  17     case $1 in
  18         -a) append=true; shift;;
  19         -v) verbose=true; shift;;
  20         --)
  21             if test "$#" -ne 2; then
  22                 usage 1>&2
  23                 exit 2
  24             fi
  25             dest="$2"
  26             shift 2
  27             ;;
  28         -*)
  29             usage 1>&2
  30             exit 2
  31             ;;
  32         *)
  33             if test "$#" -ne 1; then
  34                 usage 1>&2
  35                 exit 2
  36             fi
  37             dest="$1"
  38             shift
  39             ;;
  40     esac
  41 done
  42
  43 tmpfile="$(mktemp "$dest.sponge-XXXXXXX")"
  44
  45 clean-up()
  46 {
  47     rm -f "$tmpfile"
  48 }
  49
  50 trap clean-up EXIT
  51
  52 # Inefficient, but should clone the permissions
  53 if test -e "$dest"; then
  54    cp -Lp "$dest" "$tmpfile"
  55 fi
  56
  57 if test "$append"; then
  58     cat >> "$tmpfile"
  59 else
  60     cat > "$tmpfile"
  61 fi
  62
  63 if ! cmp -s "$tmpfile" "$dest"; then
  64     if test "$verbose"; then
  65         echo "Refreshed $dest" 1>&2
  66     fi
  67     mv "$tmpfile" "$dest"
  68 fi