join (1)

Quick Reference

Join lines of two sorted files on a common field.

  • Join two files on the first (default) field:

join {{file1}} {{file2}}

  • Join field3 of file1 with field1 of file2:

join -1 3 -2 1 {{file1}} {{file2}}

  • Produce a line for each unpairable line for file1:

join -a 1 {{file1}} {{file2}}


join - join lines of two files on a common field


join [ OPTION]... FILE1 FILE2


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.
also print unpairable lines from file FILENUM, where FILENUM is 1 or 2, corresponding to FILE1 or FILE2
replace missing input fields with EMPTY
-i, --ignore-case
ignore differences in case when comparing fields
equivalent to '-1 FIELD -2 FIELD'
obey FORMAT while constructing output line
use CHAR as input and output field separator
like -a FILENUM, but suppress joined output lines
join on this FIELD of file 1
join on this FIELD of file 2
check that the input is correctly sorted, even if all input lines are pairable
do not check that the input is correctly sorted
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
display this help and exit
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.


Written by Mike Haertel.


GNU coreutils online help: <>
Report join translation bugs to <>


comm(1), uniq(1)
Full documentation at: <>
or available locally via: info '(coreutils) join invocation'


GNU coreutils 8.29.13-0a854
Source updated
December 2, 2018
Page created
February 9, 2018
Page generated
December 2, 2018