.TH JOIN 1 
.SH NAME
join \- relational database operator
.SH SYNOPSIS
.B join
[
options
]
file1 file2
.SH DESCRIPTION
.I join
forms, on the standard output,
a join
of the two relations specified by the lines of
.I file1
and
.IR file2 .
If
.I file1
is `\-', the standard input is used.
.PP
.I file1
and 
.I file2
must be sorted in increasing ASCII collating
sequence on the fields
on which they are to be joined,
normally the first in each line.
.PP
There is one line in the output 
for each pair of lines in 
.I file1 
and 
.I file2
that have identical join fields.
The output line normally consists of the common field,
then the rest of the line from 
.IR file1 ,
then the rest of the line from
.IR file2 .
.PP
Fields are normally separated by blank, tab or newline.
In this case, multiple separators count as one, and
leading separators are discarded.
.PP
These options are recognized:
.TP
.BI \-a n
In addition to the normal output,
produce a line for each unpairable line in file
.IR n ,
where
.I n
is 1 or 2.
.TP
.BI \-e \ s
Replace empty output fields by string
.IR s .
.TP
.BI \-j n\ m
Join on the
.IR m th
field of file
.IR n .
If
.I n
is missing, use the
.IR m th
field in each file.
.TP
.BI \-o \ list
Each output line comprises the fields specifed in
.IR list ,
each element of which is 0 or has the form
.IR n . m ,
where
.I n
is a file number and
.I m
is a field number.
0 designates the join field.
.PP
.TP
.BI \-t c
Use character
.I c
as a separator (tab character).
Every appearance of
.I c
in a line is significant.
.SH "SEE ALSO"
sort(1), comm(1), awk(1)
.SH BUGS
With default field separation,
the collating sequence is that of
.IR sort\ \-b ;
with
.BR \-t ,
the sequence is that of a plain sort.
.br
The conventions of
.I join, sort, comm, uniq, look
and
.IR awk (1)
are wildly incongruent.