Linux Commands Examples

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join lines of two files on a common field

see also : comm - uniq


join [OPTION]... FILE1 FILE2

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How to print separator for all fields in join utility?

This behavior is expected per man join:

          print unpairable lines coming from file FILENUM, where FILENUM is 1 or 2, corresponding to FILE1 or FILE2

You can do it in two passes like this:

join -t: a b && join -t: -v1 a b|sed 's/:/::/'

or something along those lines.


Join with gzipped files

No, but bash (among other shells) can do process substitution.

join <(zcat foo.gz) <(zcat bar.gz)


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 whitespace. 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


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.


Copyright © 2012 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.

reporting bugs

Report join bugs to bug-coreutils[:at:]gnu[:dot:]org
GNU coreutils home page: <>
General help using GNU software: <>
Report join translation bugs to <>

see also

comm , uniq

The full documentation for join is maintained as a Texinfo manual. If the info and join programs are properly installed at your site, the command

info coreutils 'join invocation'

should give you access to the complete manual.


Written by Mike Haertel.

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