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 blanks.
When FILE1 or FILE2 (not both) is -, read standard input.
-a FILENUM
also print unpairable lines 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
--check-order
check that the input is correctly sorted, even if all
input lines are pairable
--nocheck-order
do not check that the input is correctly sorted
--header
treat the first line in each file as field headers, print
them without trying to pair them
-z, --zero-terminated
line delimiter is NUL, not newline
--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.
If FORMAT is the keyword 'auto', then the first line of each file
determines the number of fields output for each line.
Important: FILE1 and FILE2 must be sorted on the join fields.
E.g., use "sort -k 1b,1" if 'join' has no options, or use "join
-t ''" if 'sort' has no options. Note, comparisons honor the
rules specified by 'LC_COLLATE'. If the input is not sorted and
some lines cannot be joined, a warning message will be given.
