NAME

join — relational database operator

SYNOPSIS

join [-a file_number | -v file_number] [-e string] [-o list] [-t char] [-1 field] [-2 field] file1 file2

DESCRIPTION

The join utility performs an “equality join” on the specified files and writes the result to the standard output. The “join field” is the field in each file by which the files are compared. The first field in each line is used by default. There is one line in the output for each pair of lines in file1 and file2 which have identical join fields. Each output line consists of the join field, the remaining fields from file1 and then the remaining fields from file2.

The default field separators are tab and space characters. In this case, multiple tabs and spaces count as a single field separator, and leading tabs and spaces are ignored. The default output field separator is a single space character.

Many of the options use file and field numbers. Both file numbers and field numbers are 1 based, i.e., the first file on the command line is file number 1 and the first field is field number 1. The following options are available:

-a file_number: In addition to the default output, produce a line for each unpairable line in file file_number.
-e string: Replace empty output fields with string.
-o list: The -o option specifies the fields that will be output from each file for each line with matching join fields. Each element of list has either the form file_number.field, where file_number is a file number and field is a field number, or the form ‘0’ (zero), representing the join field. The elements of list must be either comma (‘,’) or whitespace separated. (The latter requires quoting to protect it from the shell, or, a simpler approach is to use multiple -o options.)
-t char: Use character char as a field delimiter for both input and output. Every occurrence of char in a line is significant.
-v file_number: Do not display the default output, but display a line for each unpairable line in file file_number. The options -v 1 and -v 2 may be specified at the same time.
-1 field: Join on the field'th field of file1.
-2 field: Join on the field'th field of file2.

When the default field delimiter characters are used, the files to be joined should be ordered in the collating sequence of sort(1), using the -b option, on the fields on which they are to be joined, otherwise join may not report all field matches. When the field delimiter characters are specified by the -t option, the collating sequence should be the same as sort(1) without the -b option.

If one of the arguments file1 or file2 is ‘-’, the standard input is used.

EXIT STATUS

The join utility exits 0 on success, and >0 if an error occurs.

EXAMPLES

Assuming a file named nobel_laureates.txt with information about some of the first Nobel Peace Prize laureates:

1901,Jean Henri Dunant,M
1901,Frederic Passy,M
1902,Elie Ducommun,M
1905,Baroness Bertha Sophie Felicita Von Suttner,F
1910,Permanent International Peace Bureau,

and a second file nobel_nationalities.txt with their nationalities:

Jean Henri Dunant,Switzerland
Frederic Passy,France
Elie Ducommun,Switzerland
Baroness Bertha Sophie Felicita Von Suttner

Join the two files using the second column from first file and the default first column from second file specifying a custom field delimiter:

$ join -t, -1 2 nobel_laureates.txt nobel_nationalities.txt
Jean Henri Dunant,1901,M,Switzerland
Frederic Passy,1901,M,France
Elie Ducommun,1902,M,Switzerland
Baroness Bertha Sophie Felicita Von Suttner,1905,F

Show only the year and the nationality of the laureate using ‘<<NULL>>’ to replace empty fields:

$ join -e "<<NULL>>" -t, -1 2 -o "1.1 2.2" nobel_laureates.txt nobel_nationalities.txt
1901,Switzerland
1901,France
1902,Switzerland
1905,<<NULL>>

Show only lines from first file which do not have a match in second file:

$ join -v1 -t, -1 2 nobel_laureates.txt nobel_nationalities.txt
Permanent International Peace Bureau,1910,

Assuming a file named capitals.txt with the following content:

Belgium,Brussels
France,Paris
Italy,Rome
Switzerland

Show the name and capital of the country where the laureate was born. This example uses nobel_nationalities.txt as a bridge but does not show any information from that file. Also see the note about sort(1) above to understand why we need to sort the intermediate result.

$ join -t, -1 2 -o 1.2 2.2 nobel_laureates.txt nobel_nationalities.txt | \
    sort -k2 -t, | join -t, -e "<<NULL>>" -1 2 -o 1.1 2.2 - capitals.txt
Elie Ducommun,<<NULL>>
Jean Henri Dunant,<<NULL>>

COMPATIBILITY

For compatibility with historic versions of join, the following options are available:

-a: In addition to the default output, produce a line for each unpairable line in both file1 and file2.
-j1 field: Join on the field'th field of file1.
-j2 field: Join on the field'th field of file2.
-j field: Join on the field'th field of both file1 and file2.
-o list ...: Historical implementations of join permitted multiple arguments to the -o option. These arguments were of the form file_number.field_number as described for the current -o option. This has obvious difficulties in the presence of files named 1.2.

These options are available only so historic shell scripts do not require modification and should not be used.

STANDARDS

The join command conforms to IEEE Std 1003.1-2001 (“POSIX.1”).