#!/usr/bin/awk -f
BEGIN {
  FS=OFS="\t"
}
{ 
  gsub(/; *$/, "", $9)        # trim trailing `;'
  split($9, pairs, / *; */)   # split attributes into pairs
  delete attr
  for (i in pairs) {
    split(pairs[i], kv, / */) # split pair into key and value
    attr[kv[1]] = kv[2]       # add it to `attr'
  }
  # fill missing fields
  if (!("gene_name" in attr))
    attr["gene_name"] = attr["gene_id"]
  if (!("transcript_id" in attr))
    attr["transcript_id"] = attr["gene_id"]
  if (!("transcript_name" in attr))
    attr["transcript_name"] = attr["transcript_id"];
  if (!("tag" in attr))
    attr["tag"] = "\"basic\"";
  # recreate the attributes field
  attr_all = sep = ""
  for (k in attr) {
    attr_all = attr_all sep k " " attr[k]
    sep = "; "
  }
  # update the record with new attributes
  $9 = attr_all";" 
}
1 # print record