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GNU coreutils 8.32
March 2020


The basic file, shell and text manipulation utilities of the GNU operating system


coreutils common optional components


Documentation for the GNU Core Utilities


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
-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’
obey FORMAT while constructing output line
-t CHAR use CHAR as input and output field separator
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 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
--help 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: <>
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Copyright © 2020 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.


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


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