Section (1) join

Linux manual pages Section 1  


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 _zsingle_quotesz_−1 FIELD −2 FIELD_zsingle_quotesz_


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 _zsingle_quotesz_FILENUM.FIELD_zsingle_quotesz_ or _zsingle_quotesz_0_zsingle_quotesz_. 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 _zsingle_quotesz_auto_zsingle_quotesz_, 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 _zsingle_quotesz_join_zsingle_quotesz_ has no options, or use join −t _zsingle_quotesz__zsingle_quotesz_ if _zsingle_quotesz_sort_zsingle_quotesz_ has no options. Note, comparisons honor the rules specified by _zsingle_quotesz_LC_COLLATE_zsingle_quotesz_. 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 any translation bugs to <>


comm(1), uniq(1)

Full documentation <>

or available locally via: info _zsingle_quotesz_(coreutils) join invocation_zsingle_quotesz_


Copyright © 2019 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.