remove duplicate lines after first word in sentace linux terminal

Question

I was looking to remove duplicates of lines of text but after a space from the first word in this format;

apples blue
apples green
apples are sometimes red
pairs green
pairs black
potato brown
lemon
...

Anything after a space on each line would get disregarded, then removed duplicates.

Would end up with;

apples
pairs
potato
lemon

I was hopefully looking for a way this could be done in linux terminal like;

command file_in.txt single_sout.txt

Thanks guys!

Answer 1

Try this one-liner:

cut -d " " -f 1 file_in.txt | uniq > file_out.txt

First you use the cut command with the delimiter -d " ", and then get the first field with -f 1 from the file file_in.txt. Then pipe the result into the uniq command, and that will remove duplicates from the list. Finally you redirect the result to file_out.txt.