coreutils: Set operations

 
 8.3.6 Union, Intersection and Difference of files
 -------------------------------------------------
 
 Combine ‘sort’, ‘uniq’ and ‘join’ to perform the equivalent of set
 operations on files:
 
 Command                              outcome
 --------------------------------------------------------------------------
 ‘sort -u file1 file2’                Union of unsorted files
                                      
 ‘sort file1 file2 | uniq -d’         Intersection of unsorted files
                                      
 ‘sort file1 file1 file2 | uniq’      Difference of unsorted files
                                      
 ‘sort file1 file2 | uniq -u’         Symmetric Difference of unsorted
                                      files
                                      
 ‘join -t'' -a1 -a2 file1 file2’      Union of sorted files
                                      
 ‘join -t'' file1 file2’              Intersection of sorted files
                                      
 ‘join -t'' -v2 file1 file2’          Difference of sorted files
                                      
 ‘join -t'' -v1 -v2 file1 file2’      Symmetric Difference of sorted
                                      files
                                      
 
    All examples above operate on entire lines and not on specific
 fields: ‘sort’ without ‘-k’ and ‘join -t''’ both consider entire lines
 as the key.