join - relational database operator

     join [-an] [-e s] [-o list] [-tc] file1 file2

     Join forms, on the standard output, a join of the two relations specified
     by  the lines of file1 and file2.  If file1 is `-', the standard input is

     File1 and file2 must be sorted in increasing ASCII collating sequence  on
     the  fields  on  which  they are to be joined, normally the first in each

     There is one line in the output for each pair of lines in file1 and file2
     that  have  identical  join fields.  The output line normally consists of
     the common field, then the rest of the line from file1, then the rest  of
     the line from file2.

     Fields are normally separated by blank, tab or newline.   In  this  case,
     multiple separators count as one, and leading separators are discarded.

     These options are recognized:

     -an  In addition to the normal output, produce a line for each unpairable
          line in file n, where n is 1 or 2.

     -e s Replace empty output fields by string s.

     -o list
          Each output line  comprises  the  fields  specified  in  list,  each
          element of which has the form n.m, where n is a file number and m is
          a field number.

     -tc  Use character c as a separator (tab character).  Every appearance of
          c in a line is significant.

     sort(1), comm(1), awk(1).

     With default field separation, the collating sequence is that of sort -b;
     with -t, the sequence is that of a plain sort.

     The conventions of join, sort, comm, uniq, look  and  awk(1)  are  wildly