I want to print 1 version of Duplicates and remove unique lines in bash linux -

the input follows:

mark john marry mark john 

and output should be:

mark john 

how in bash file linux.

sort | uniq -d 

for example:

$ cat file mark john marry mark john   $ cat file | sort | uniq -d john mark 

to preserve order, can use more obscure awk command:

$ awk 'a[$0]++ == 1' file mark john