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 FILENUM

print unpairable lines coming from file FILENUM, where FILENUM is 1 or 2, corresponding to FILE1 or FILE2

-e EMPTY

replace missing input fields with EMPTY

-i, --ignore-case ignore differences in case when comparing fields

-j FIELD

equivalent to `-1 FIELD -2 FIELD'

-o FORMAT

obey FORMAT while constructing output line

-t CHAR

use CHAR as input and output field separator

-v FILENUM

like -a FILENUM, but suppress joined output lines

-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 `FILENUM.FIELD' or `0'. Default FORMAT outputs the join field, the remaining fields from FILE1, the remaining fields from FILE2, all separated by CHAR.

Important: FILE1 and FILE2 must be sorted on the join fields.

info join

should give you access to the complete manual.