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.\"
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.\"	@(#)join.1	8.3 (Berkeley) 4/28/95
.\"
.Dd April 28, 1995
.Dt JOIN 1
.Os
.Sh NAME
.Nm join
.Nd relational database operator
.Sh SYNOPSIS
.Nm join
.Oo
.Fl a Ar file_number | Fl v Ar file_number
.Oc
.Op Fl e Ar string
.Op Fl j Ar file_number field
.Op Fl o Ar list
.Bk -words
.Ek
.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.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl a Ar file_number
In addition to the default output, produce a line for each unpairable
line in file
.Ar file_number .
(The argument to
.Fl a
must not be preceded by a space; see the
.Sx STANDARDS
section.)
.It Fl e Ar string
Replace empty output fields with
.Ar string .
.It Fl o Ar list
Specifies the fields that will be output from each file for
each line with matching join fields.
Each element of
.Ar list
has the form
.Dq file_number.field ,
where
.Ar file_number
is a file number and
.Ar field
is a field number.
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 Ar 1
and
.Fl v Ar 2
may be specified at the same time.
.It Fl 1 Ar field
Join on the
.Ar field Ns 'th
field of file 1.
.It Fl 2 Ar field
Join on the
.Ar field Ns 'th
field of file 2.
.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
.Dq - ,
the standard input is used.
.\" XXX - use .br as a work-around for an apparent bug in mdoc
.br
.Pp
The
.Nm
utility exits 0 on success or >0 if an error occurred.
.Sh SEE ALSO
.Xr awk 1 ,
.Xr comm 1 ,
.Xr paste 1 ,
.Xr sort 1 ,
.Xr uniq 1
.Sh STANDARDS
For compatibility with historic versions of
.Nm join ,
the following options are available:
.Bl -tag -width Fl
.It Fl a
In addition to the default output, produce a line for each unpairable line
in both file 1 and file 2.
(To distinguish between this and
.Fl a Ar file_number ,
.Nm
currently requires that the latter not include any whitespace.)
.It Fl j1 Ar field
Join on the
.Ar field Ns 'th
field of file 1.
.It Fl j2 Ar field
Join on the
.Ar field Ns 'th
field of file 2.
.It Fl j Ar field
Join on the
.Ar field Ns 'th
field of both file 1 and file 2.
.It Fl o Ar list ...
Historical implementations of
.Nm
permitted multiple arguments to the
.Fl o
option.
These arguments were of the form
.Dq file_number.field_number
as described for the current
.Fl o
option.
This has obvious difficulties in the presence of files named
.Dq 1.2 .
.El
.Pp
These options are available only so historic shell scripts don't require
modification and should not be used.
.Pp
The
.Nm
command is expected to be
.St -p1003.2
compatible.