parse_lnk.sh

_lnk_read_block() {
    _lnkpath=$1
    _offset=$2
    _length=$3
    od --endian=little -tdI -An -j "$_offset" -N "$_length" "$_lnkpath" | tr -d '\n '
}

_lnk_readstr_utf16() {
    _lnkpath=$1
    _offset=$2
    _length=$3
    _unicode=$4
    _result=''
    if [ "$_unicode" = 1 ]; then
        # stop at first \0 by getting offset and overriding _length
        _nul_offset=$(od -w2 -v -t x2 -Ad -j "$_offset" -N "$_length" "$_lnkpath" | awk '$2 == "0000" {print $1+0;exit}')
        [ -n "$_nul_offset" ] && _length=$((_nul_offset-_offset))

        _result=$(dd skip="$_offset" count="$_length" if="$_lnkpath" bs=1 status=none | iconv -f UTF-16LE -t UTF-8)
    else
        _result=$(od -S1 -An -j "$_offset" -N "$_length" "$_lnkpath")
    fi
    printf '%s' "$_result" | sed 's/\\/\\\\/g'
}

_lnk_read_stringdata_len() {
    _lnkpath=$1
    _offset=$2
    _unicode=$3
    _len=$(_lnk_read_block "$_lnkpath" "$_offset" 2) # CountCharacters
    if [ "$_unicode" = 1 ]; then
        printf '%s' $((_len*2))
    else
        printf '%s' "$_len"
    fi
}

_lnk_read_stringdata() {
    _lnkpath=$1
    _offset=$2
    _length=$3
    _unicode=$4
    if [ "$_length" -gt 0 ]; then
        printf '%s' "$(_lnk_readstr_utf16 "$_lnkpath" $((_offset+2)) "$_length" "$_unicode")"
    fi
}

# Parse Windows .lnk for data
# Based on these documentation: 
# - https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-shllink/16cb4ca1-9339-4d0c-a68d-bf1d6cc0f943
# - https://github.com/libyal/liblnk/tree/main/documentation
parse_lnk() {
  _lnkpath="$1"

  # https://github.com/libyal/liblnk/blob/main/documentation/Windows%20Shortcut%20File%20(LNK)%20format.asciidoc#21-data-flags
  _flags_oct=$(od -An -j 20 -N 1 "$_lnkpath" | tr -d '\n ')
  _flags=$(printf 'ibase=8; %s\n' "$_flags_oct" | bc)

  # https://github.com/libyal/liblnk/blob/main/documentation/Windows%20Shortcut%20File%20(LNK)%20format.asciidoc#3-link-target-identifier
  _itemlist_count=$(_lnk_read_block "$_lnkpath" 76 2)

  # LinkInfo
  # https://github.com/libyal/liblnk/blob/main/documentation/Windows%20Shortcut%20File%20(LNK)%20format.asciidoc#4-location-information
  _location_offset=$((_itemlist_count+78)) # skip guid
  _link_info_length=$(_lnk_read_block "$_lnkpath" $_location_offset 4)            # LinkInfoSize
  _link_info_header_size=$(_lnk_read_block "$_lnkpath" $((_location_offset+4)) 4) # LinkInfoHeaderSize
  _link_info_flags=$(_lnk_read_block "$_lnkpath" $((_location_offset+8)) 4)       # LinkInfoFlags
  _basepath_offset=$(_lnk_read_block "$_lnkpath" $((_location_offset+16)) 4)      # LocalBasePathOffset

  _basepath_is_unicode=0
  # Use unicode offset instead
  if [ "$_link_info_header_size" -gt 28 ]; then
    _basepath_offset=$(_lnk_read_block "$_lnkpath" $((_location_offset+28)) 4) # LocalBasePathOffsetUnicode
    _basepath_is_unicode=1
  fi

  _localpath_offset=$((_location_offset+_basepath_offset))
  _localpath_end=$((_location_offset+_link_info_length))
  _localpath_length=$((_localpath_end-_localpath_offset))

  _localpath=$(_lnk_readstr_utf16 "$_lnkpath" $_localpath_offset $_localpath_length $_basepath_is_unicode) # LocalBasePath or LocalBasePathUnicode

  printf 'LocalBasePath:%s\n' "$_localpath"

  # StringData
  # STRING_DATA = [NAME_STRING] [RELATIVE_PATH] [WORKING_DIR] [COMMAND_LINE_ARGUMENTS] [ICON_LOCATION]
  # https://github.com/libyal/liblnk/blob/main/documentation/Windows%20Shortcut%20File%20(LNK)%20format.asciidoc#5-data-strings
  
  _stringdata_is_unicode=0
  # IsUnicode
  [ "$((_flags & 0x00000080))" -ne 0 ] && _stringdata_is_unicode=1

  _stringdata_offset=$_localpath_end
  # HasName HasRelativePath HasWorkingDir HasArguments HasIconLocation
  for i in 0x00000004 0x00000008 0x00000010 0x00000020 0x00000040 ; do
    if [ "$((_flags & i))" -ne 0 ]; then
      _stringdata_length=$(_lnk_read_stringdata_len "$_lnkpath" "$_stringdata_offset" $_stringdata_is_unicode)
      _stringdata_value="$(_lnk_read_stringdata "$_lnkpath" "$_stringdata_offset" "$_stringdata_length" $_stringdata_is_unicode)"
      _stringdata_offset=$((_stringdata_offset+_stringdata_length))
      [ $_stringdata_is_unicode = 1 ] && _stringdata_offset=$((_stringdata_offset+2))
      if [ -n "$_stringdata_value" ]; then
        case "$i" in
          0x00000004) printf 'NAME_STRING:';;
          0x00000008) printf 'RELATIVE_PATH:';;
          0x00000010) printf 'WORKING_DIR:';;
          0x00000020) printf 'COMMAND_LINE_ARGUMENTS:';;
          0x00000040) printf 'ICON_LOCATION:';;
        esac
        printf '%s\n' "$_stringdata_value"
      fi
    fi
  done
}