Bash script for a better version of the `uniq` shell command

uniq

#!/bin/bash
# uniq - The default version of the uniq command only finds uniques that are adjacent
#        and has no flag to find non-adjacent lines... so pretty useless. This is a
#        bash script that actually does what you would expect uniq to do.

# for every piped in line:
for w in $(cat); do
  # if we haven't already added it before
  if [[ "$(grep -o "$w" <<< "$once")" == "" ]]; then
    # add it + newline
    once="$once$w\n"
  fi
done

# print everything except the last empty newline
echo -e $once | head -n-1