Extract unique lines from a file in order of their first occurence in bash

Question

I have a file with a list of strings. I'd like to extract out the unique strings, in the order that they first appear in the file.

So, for instance, if my file contains:

foo
bar
foo
bar
baz
bar
foo

I'd like to output:

foo
bar
baz

If I just wanted the unique values, I could use sort input|uniq, but this sorts my result alphabetically.

Answer 1

Quite simple in awk:

awk '!a[$0]++'