sed: uniq -u

1 
1 7.19 Remove All Duplicated Lines
1 ================================
1 
1 This script prints only unique lines, like 'uniq -u'.
1 
1      #!/usr/bin/sed -f
1 
1      # Search for a duplicate line --- until that, print what you find.
1      $b
1      N
1      /^\(.*\)\n\1$/ ! {
1          P
1          D
1      }
1 
1      :c
1      # Got two equal lines in pattern space.  At the
1      # end of the file we simply exit
1      $d
1 
1      # Else, we keep reading lines with N until we
1      # find a different one
1      s/.*\n//
1      N
1      /^\(.*\)\n\1$/ {
1          bc
1      }
1 
1      # Remove the last instance of the duplicate line
1      # and go back to the top
1      D
1