Manual: gnujoin

JOIN(1)							User Commands						     JOIN(1)

NAME
       join - join lines of two files on a common field

SYNOPSIS
       join [OPTION]... FILE1 FILE2

DESCRIPTION
       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 STRING
	      replace missing (empty) input fields with STRING; I.e., missing fields specified with '-12jo' options

       -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.  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.

AUTHOR
       Written by Mike Haertel.

REPORTING BUGS
       GNU coreutils online help: 
       Report any translation bugs to 

SEE ALSO
       comm(1), uniq(1)

       Full documentation 
       or available locally via: info '(coreutils) join invocation'

       Packaged by Ubuntu (9.7-3ubuntu2)
       Copyright © 2025 Free Software Foundation, Inc.
       License GPLv3+: GNU GPL version 3 or later .
       This is free software: you are free to change and redistribute it.
       There is NO WARRANTY, to the extent permitted by law.

GNU coreutils 9.7					January 2026						     JOIN(1)