Extract line that don't repeat

Question

I have a csv file with duplicate lines and I need to extract only the non repeating lines.

For example, I have

12
13
14
12
13
15

and the desired output is:

14
15

Answer 1

To find the unique lines in a file you can use uniq -u (required sorted file):

$ sort file | uniq -u    
14
15

An alternative method using awk:

$ awk '{a[$0]++}END{for(k in a)if(a[k]==1)print k}' file
14
15