For each pair of input lines with identical join fields, write a line to standard output. The default join field is the first, delimited by whitespace. When FILE1 or FILE2 (not both) is -, read standard input.

-a SIDE print unpairable lines coming from file SIDE
-e EMPTY replace missing input fields with EMPTY
-i, --ignore-case ignore differences in case when comparing fields
-o FORMAT obey FORMAT while constructing output line
-p if one field is a prefix of the other, count that as a match
-t CHAR use CHAR as input and output field separator
-T CHAR use CHAR as output field separator
-v SIDE like -a SIDE, but suppress joined output lines
-x FILE like -a 1, but send unpairable lines to FILE
-y FILE like -a 2, but send unpairable lines to FILE
-1 FIELD join on this FIELD of file 1
-2 FIELD join on this FIELD of file 2
--help display this help and exit
--version output version information and exit

Unless -t CHAR is given, leading blanks separate fields and are ignored, else fields are separated by CHAR. Any FIELD is a field number counted from 1. FORMAT is one or more comma or blank separated specifications, each being `SIDE.FIELD' or `0'. Default FORMAT outputs the join field, the remaining fields from FILE1, the remaining fields from FILE2, all separated by CHAR.