utils-std

join.1 (7285B)

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.\"	@(#)join.1	8.3 (Berkeley) 4/28/95
.\"
.Dd June 20, 2020
.Dt JOIN 1
.Os
.Sh NAME
.Nm join
.Nd relational database operator
.Sh SYNOPSIS
.Nm
.Oo
.Fl a Ar file_number | Fl v Ar file_number
.Oc
.Op Fl e Ar string
.Op Fl o Ar list
.Op Fl t Ar char
.Op Fl 1 Ar field
.Op Fl 2 Ar field
.Ar file1
.Ar file2
.Sh DESCRIPTION
The
.Nm
utility performs an
.Dq equality join
on the specified files
and writes the result to the standard output.
The
.Dq 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
.Ar file1
and
.Ar file2
which have identical join fields.
Each output line consists of the join field, the remaining fields from
.Ar file1
and then the remaining fields from
.Ar file2 .
.Pp
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.
.Pp
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:
.Bl -tag -width indent
.It Fl a Ar file_number
In addition to the default output, produce a line for each unpairable
line in file
.Ar file_number .
.It Fl e Ar string
Replace empty output fields with
.Ar string .
.It Fl o Ar list
The
.Fl o
option specifies the fields that will be output from each file for
each line with matching join fields.
Each element of
.Ar list
has either the form
.Ar file_number . Ns Ar field ,
where
.Ar file_number
is a file number and
.Ar field
is a field number, or the form
.Ql 0
.Pq zero ,
representing the join field.
The elements of list must be either comma
.Pq Ql \&,
or whitespace separated.
(The latter requires quoting to protect it from the shell, or, a simpler
approach is to use multiple
.Fl o
options.)
.It Fl t Ar char
Use character
.Ar char
as a field delimiter for both input and output.
Every occurrence of
.Ar char
in a line is significant.
.It Fl v Ar file_number
Do not display the default output, but display a line for each unpairable
line in file
.Ar file_number .
The options
.Fl v Cm 1
and
.Fl v Cm 2
may be specified at the same time.
.It Fl 1 Ar field
Join on the
.Ar field Ns 'th
field of
.Ar file1 .
.It Fl 2 Ar field
Join on the
.Ar field Ns 'th
field of
.Ar file2 .
.El
.Pp
When the default field delimiter characters are used, the files to be joined
should be ordered in the collating sequence of
.Xr sort 1 ,
using the
.Fl b
option, on the fields on which they are to be joined, otherwise
.Nm
may not report all field matches.
When the field delimiter characters are specified by the
.Fl t
option, the collating sequence should be the same as
.Xr sort 1
without the
.Fl b
option.
.Pp
If one of the arguments
.Ar file1
or
.Ar file2
is
.Sq Fl ,
the standard input is used.
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
Assuming a file named
.Pa nobel_laureates.txt
with information about some of the first Nobel Peace Prize laureates:
.Bd -literal -offset indent
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,
.Ed
.Pp
and a second file
.Pa nobel_nationalities.txt
with their nationalities:
.Bd -literal -offset indent
Jean Henri Dunant,Switzerland
Frederic Passy,France
Elie Ducommun,Switzerland
Baroness Bertha Sophie Felicita Von Suttner
.Ed
.Pp
Join the two files using the second column from first file and the default first
column from second file specifying a custom field delimiter:
.Bd -literal -offset indent
$ 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
.Ed
.Pp
Show only the year and the nationality of the laureate using
.Ql <<NULL>>
to replace empty fields:
.Bd -literal -offset indent
$ 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>>
.Ed
.Pp
Show only lines from first file which do not have a match in second file:
.Bd -literal -offset indent
$ join -v1 -t, -1 2 nobel_laureates.txt nobel_nationalities.txt
Permanent International Peace Bureau,1910,
.Ed
.Pp
Assuming a file named
.Pa capitals.txt
with the following content:
.Bd -literal -offset indent
Belgium,Brussels
France,Paris
Italy,Rome
Switzerland
.Ed
.Pp
Show the name and capital of the country where the laureate was born.
This example uses
.Pa nobel_nationalities.txt
as a bridge but does not show any information from that file.
Also see the note about
.Xr sort 1
above to understand why we need to sort the intermediate result.
.Bd -literal -offset indent
$ join -t, -1 2 -o "1.2 2.2" nobel_laureates.txt nobel_nationalities.txt | \e
    sort -k2 -t, | join -t, -e "<<NULL>>" -1 2 -o "1.1 2.2" - capitals.txt
Elie Ducommun,<<NULL>>
Jean Henri Dunant,<<NULL>>
.Ed
.Sh COMPATIBILITY
Compatibility with
.Fl a
and multi-operand
.Fl o
from historical versions of
.Nm
got dropped, compatibility with
.Fl j Ar field
is kept for now.
.Sh SEE ALSO
.Xr awk 1 ,
.Xr comm 1 ,
.Xr paste 1 ,
.Xr sort 1 ,
.Xr uniq 1
.Sh STANDARDS
.Nm
should be compliant with the
IEEE Std 1003.1-2024 (“POSIX.1”)
specification.