How to find the particular text stored in the file “data.txt” and it occurs only once

Question

The line I seek is stored in the file data.txt and is the only line of text that occurs only once.

How do I go about finding that particular line using linux?

Answer 1

And one with only one tool in use, awk:

awk '{a[$1]++}END{for(i in a){if(a[i] == 1){print i} }}' data.txt