-e  string
       Replace empty output fields in the list selected by -o with the string string.

-o  list
       Construct the output line to comprise the fields specified in list, each element  of  which  shall
       have one of the following two forms:

        1. file_number.field,  where  file_number  is  a file number and field is a decimal integer field
           number

        2. 0 (zero), representing the join field

The elements of list shall be either comma-separated or <blank>-separated, as specified in Guideline 8 of
the  Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines. The fields
specified by list shall be written for all selected output lines. Fields selected by  list  that  do  not
appear  in  the  input  shall  be treated as empty output fields.  (See the -e option.) Only specifically
requested fields shall be written. The application shall ensure  that  list  is  a  single  command  line
argument.

-t  char
       Use  character char as a separator, for both input and output.  Every appearance of char in a line
       shall be significant. When this option is specified, the collating sequence shall be the  same  as
       sort without the -b option.

-v  file_number

       Instead  of the default output, produce a line only for each unpairable line in file_number, where
       file_number is 1 or 2. If both -v1 and -v2 are specified, all unpairable lines shall be output.

-1  field
       Join on the fieldth field of file 1. Fields are decimal integers starting with 1.

-2  field
       Join on the fieldth field of file 2. Fields are decimal integers starting with 1.