join.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH join 1
.SH Name
join \- join files
.SH Syntax
.B "join [ \-a \fIn\fP] [ \-e \fIstring\fP] [ \-j \fI n m\fP] [ \-o \fIlist\fP] [ \-t \fIc\fP] \fI file1 file2\fP"
.SH Description
.NXR "join command"
.NXR "file" "comparing"
.NXR "file" "combining"
.NXR "join command" "sort command"
.NXR "join command" "comm command"
.NXR "relational data base operator"
The
.PN join
command compares a field in 
.I file1 
to a field in 
.IR file2 .
If the two fields match, the
.PN join
command combines the line in 
.I file1
that contains the field with
the line in 
.I file2 
that contains the field.  The command writes
its output to standard output.  If you specify a hyphen (-) in the
.I file1
argument,
.PN join
compares standard input to the contents of 
.IR file2 .
.PP
The 
.PN join
command compares and combines the input files one line at a time. Each
line in the input file contains one field that 
.PN join
uses to determine if two lines should be joined.  This field is called
the join field. By default, the
.PN join
command uses the first field in each line as the join field.   
The command compares the join field in the first line of 
.I file1
to the join field in the first line of 
.IR file2 .  
If the two
fields match, the command joins the lines.  The command then compares
the join fields in the second line of both files, and so on.
.PP
In the input files, fields are separated by tab or space
characters.  The
.PN join 
command reads data from the first field until it encounters a tab or space 
character, which terminates the
first field.   By default, the
command ignores tab and space characters, so the next character that is not
a tab or space begins the
second field.  The second field is terminated by the tab or space that
follows it, and the third field begins with the next character that is
not a tab or space.  The 
.PN join
command reads fields in this way until it encounters
a new line character.
Any number of tabs or spaces can separate two fields, and any number
of newline characters can separate two lines.
.PP
Both 
.I file1
and 
.I file2
must be ordered in the collating sequence of the
.PN sort \-b
command on the fields that the two files are to be joined. By default, 
.PN join 
uses the first field in each line and collates the same as 
.PN sort
.PN \-b .
.PP
To create output, the 
.PN join 
command writes the join field, followed by the remaining fields in the
line from 
.I file1, 
followed by the remaining fields in the line
from 
.I file2
to the output file.  The following demonstrates how lines
in the  output appear by default:
.EX
join_field file1.field2 file1.field3 file1.field4 file2.field2 file2.field3
.EE
.PP
By default, the 
.PN join
command ignores lines that do not contain identical join fields.  The
command writes no output for these lines.
.PP
You can change how 
.PN join
creates output using command options.  For example, you can
cause the command to write output for lines that do not
contain identical join fields.  You can also specify a 
.I list
using the
.PN \-o
option.  In
.I list,
you supply a list of specifiers in the form
.I file.field, 
where 
.I file
is either 1 or 2 and 
.I field
is the number of the field.  For example, 1.2 specifies the second field
in the first file and 2.4 specifies the fourth field in the second
file. The following demonstrates how lines in the output appear if you
use these two specifiers:
.EX
file1.field2 field2.field4
.EE
.SS International Environment
.IP LC_COLLATE 15
If this environment variable is set and
valid,
.PN join
uses the international language database named in the definition to
determine collation rules.
.IP LC_CTYPE
If this environment variable is set and valid,
.PN join
uses the international language database named in the definition to
determine character classification rules.
.IP LANG
If this environment variable is set and valid 
.PN join
uses the international language database named in the definition to
determine collation and character classification rules.  If LC_COLLATE
or LC_CTYPE is defined their definition supercedes the definition of
LANG.
.SH Options
.IP \fB\-a[\fIn\fR] 12
Write lines that contain unmatched join fields to the output file.  
You can cause the
command to write unmatched lines from only one file using 
.IR n .
If you specify 1 in 
.IR n ,
.PN join
writes unmatched lines only from file 1.  If you specify 2,
.PN join
writes unmatched lines only from file 2.
.IP
If you omit the
.PN \-a 
option, 
.PN join
writes no output for unmatched lines.
.IP "\fB\-\|e\fI s\fR" 12 
Writes the string you specify in 
.I s
to the output if you
specify a nonexistent field in the 
.I list
for the
.PN \-o
option.  For example, if lines in file 2 contain only three fields,
and you specify 2.4 in 
.IR list ,
.PN join
writes 
.I s
in place of the nonexistent field.
.IP "\fB\-\|j\fIn m\fR" 12
Defines field \fIm\fP in file \fIn\fP to be the join field. The
.PN join
command compares the field you specify in the
.PN \-j
option to the default join field in the other file.
If you omit
.IR n ,
the 
.PN join
command uses 
the 
.IR m th
field in both files.
.IP "\fB\-\|1\fI m\fR"
Use the 
.I m
th
field in the first file as the join field.  This option is equivalent
to using
.PN \-j 1 
.IR m .
.IP "\fB\-\|2\fI m\fR"
Use the 
.I m 
field in the second file as the join field.  This option is equivalent
to using
.PN \-j 2 
.IR m .
.IP "\fB\-\|o\fI list\fR" 12
Output the joined data according to 
.IR list .
The specifiers in
.I list
have the format 
.IR file.field ,
where 
.I file
is either 1 or 2 and 
.I field
is the number of the field.
.IP \fB\-t\fIc\fR 12
Recognize the tab character 
.IR c .
The presence of 
.I c
in a line is significant, both for comparing join fields and creating output.
.SH Restrictions
.NXR "join command" "restricted" 
If you specify the
.PN \-t
option, the 
.PN join 
command collates the same as
.PN sort
with no options.
.SH Examples
Suppose that by issuing the following 
.PN cat
commands, you display the files shown in the example:
.EX
% cat file_1
apr     15
aug     20
dec     18
feb     05
% cat file_2
apr     06
aug     14
date
feb     15
.EE
Both files are sorted in ascending order.
.PP
If you issue the 
.PN join
command without options, the output appears as follows:
.EX
% join file_1 file_2
apr 15 06
aug 20 14
feb 05 15
.EE
The third line in each input file is not joined in the output because
the join fields (date and dec) do not match.
.PP
To join the lines in these files and format the output so that the
second field from each file appears first and the first (join) field
appears second, issue
the following command:
.EX
% join \-o 1.2 1.1 2.2 2.1 file_1 file_2
15 apr 06 apr
20 aug 14 aug
05 feb 15 feb
.EE
To write lines
that are unmatched to the output, issue the following command:
.EX
% join \-a file_1 file_2
apr 15 06
aug 20 14
date
dec 18
feb 05 15
.EE
.SH See Also
awk(1), comm(1), sort(1), sort5(1), environ(5int)