Manual Page - join(1p)
Manual Reference Pages - JOIN (P)
NAME
join - relational database operator
CONTENTS
Synopsis
Description
Options
Operands
Stdin
Input Files
Environment Variables
Asynchronous Events
Stdout
Stderr
Output Files
Extended Description
Exit Status
Consequences Of Errors
Application Usage
Examples
Rationale
Future Directions
See Also
Copyright
SYNOPSIS
join [-a file_number | -v file_number][-e
string][-o list][-t char]
[-1 field][-2
field]
file1 file2
DESCRIPTION
The join utility shall perform an equality join on the files
file1 and file2. The joined files shall be
written to the standard output.
The join field is a field in each file on which the files are compared.
The join utility shall write one line in the
output for each pair of lines in file1 and file2 that
have identical join fields. The output line by default shall
consist of the join field, then the remaining fields from file1,
then the remaining fields from file2. This format
can be changed by using the -o option (see below). The -a
option can be used to add unmatched lines to the output.
The -v option can be used to output only unmatched lines.
The files file1 and file2 shall be ordered in the collating
sequence of sort -b on the fields on which they shall
be joined, by default the first in each line.
All selected output shall be written in the same collating sequence.
The default input field separators shall be <blank>s. In this case,
multiple separators shall count as one field
separator, and leading separators shall be ignored. The default output
field separator shall be a <space>.
The field separator and collating sequence can be changed by using
the -t option (see below).
If the same key appears more than once in either file, all combinations
of the set of remaining fields in file1 and the
set of remaining fields in file2 are output in the order of
the lines encountered.
If the input files are not in the appropriate collating sequence,
the results are unspecified.
OPTIONS
The join utility shall conform to the Base Definitions volume
of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
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-a file_number
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Produce a line for each unpairable line in file file_number,
where file_number is 1 or 2, in addition to the default
output. If both -a1 and -a2 are specified, all unpairable
lines shall be output.
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-e string
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Replace empty output fields in the list selected by -o with
the string string.
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-o list
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Construct the output line to comprise the fields specified in list,
each element of which shall have one of the
following two forms:
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1.
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file_number.field, where file_number is a file number
and field is a decimal integer field number
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2.
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0 (zero), representing the join field
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The elements of list shall be either comma-separated or <blank>-separated,
as specified in Guideline 8 of the Base
Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility
Syntax
Guidelines. The fields specified by list shall be written for
all selected output lines. Fields selected by list
that do not appear in the input shall be treated as empty output fields.
(See the -e option.) Only specifically requested
fields shall be written. The application shall ensure that list
is a single command line argument.
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-t char
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Use character char as a separator, for both input and output.
Every appearance of char in a line shall be
significant. When this option is specified, the collating sequence
shall be the same as sort without the -b option.
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-v file_number
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Instead of the default output, produce a line only for each unpairable
line in file_number, where file_number is 1 or
2. If both -v1 and -v2 are specified, all unpairable lines
shall be output.
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-1 field
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Join on the fieldth field of file 1. Fields are decimal integers
starting with 1.
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-2 field
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Join on the fieldth field of file 2. Fields are decimal integers
starting with 1.
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OPERANDS
The following operands shall be supported:
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file1, file2
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A pathname of a file to be joined. If either of the file1 or
file2 operands is ’-’ , the standard input
shall be used in its place.
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STDIN
The standard input shall be used only if the file1 or file2
operand is ’-’ . See the INPUT FILES
section.
INPUT FILES
The input files shall be text files.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of
join:
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LANG
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Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
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LC_ALL
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If set to a non-empty string value, override the values of all the
other internationalization variables.
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LC_COLLATE
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Determine the locale of the collating sequence join expects
to have been used when the input files were sorted.
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LC_CTYPE
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Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files).
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LC_MESSAGES
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Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
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NLSPATH
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Determine the location of message catalogs for the processing of LC_MESSAGES
.
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ASYNCHRONOUS EVENTS
Default.
STDOUT
The join utility output shall be a concatenation of selected
character fields. When the -o option is not
specified, the output shall be:
"%s%s%s\n", <join field>, <other file1 fields>,
<other file2 fields>
If the join field is not the first field in a file, the <other file fields>
for that file shall be:
<fields preceding join field>, <fields following join field>
When the -o option is specified, the output format shall be:
"%s\n", <concatenation of fields>
where the concatenation of fields is described by the -o option,
above.
For either format, each field (except the last) shall be written with
its trailing separator character. If the separator is the
default ( <blank>s), a single <space> shall be written after each
field (except the last).
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
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0
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All input files were output successfully.
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>0
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An error occurred.
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CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
Pathnames consisting of numeric digits or of the form string.string
should not be specified directly following the
-o list.
EXAMPLES
The -o 0 field essentially selects the union of the join fields.
For example, given file phone:
!Name Phone Number
Don +1 123-456-7890
Hal +1 234-567-8901
Yasushi +2 345-678-9012
and file fax:
!Name Fax Number
Don +1 123-456-7899
Keith +1 456-789-0122
Yasushi +2 345-678-9011
(where the large expanses of white space are meant to each represent
a single <tab>), the command:
join -t "<tab>" -a 1 -a 2 -e ’(unknown)’ -o 0,1.2,2.2 phone fax
would produce:
!Name Phone Number Fax Number
Don +1 123-456-7890 +1 123-456-7899
Hal +1 234-567-8901 (unknown)
Keith (unknown) +1 456-789-0122
Yasushi +2 345-678-9012 +2 345-678-9011
Multiple instances of the same key will produce combinatorial results.
The following:
fa:
a x
a y
a z
fb:
a p
will produce:
a x p
a y p
a z p
And the following:
fa:
a b c
a d e
fb:
a w x
a y z
a o p
will produce:
a b c w x
a b c y z
a b c o p
a d e w x
a d e y z
a d e o p
RATIONALE
The -e option is only effective when used with -o because,
unless specific fields are identified using -o,
join is not aware of what fields might be empty. The exception
to this is the join field, but identifying an empty join
field with the -e string is not historical practice and some
scripts might break if this were changed.
The 0 field in the -o list was adopted from the Tenth Edition
version of join to satisfy international objections
that the join in the base documents does not support the "full
join" or "outer join" described in relational database
literature. Although it has been possible to include a join field
in the output (by default, or by field number using -o),
the join field could not be included for an unpaired line selected
by -a. The -o 0 field essentially selects the
union of the join fields.
This sort of outer join was not possible with the join commands
in the base documents. The -o 0 field was chosen
because it is an upwards-compatible change for applications. An alternative
was considered: have the join field represent the union
of the fields in the files (where they are identical for matched lines,
and one or both are null for unmatched lines). This was not
adopted because it would break some historical applications.
The ability to specify file2 as - is not historical practice;
it was added for completeness.
The -v option is not historical practice, but was considered
necessary because it permitted the writing of only
those lines that do not match on the join field, as opposed to the
-a option, which prints both lines that do and do not
match. This additional facility is parallel with the -v option
of grep.
Some historical implementations have been encountered where a blank
line in one of the input files was considered to be the end
of the file; the description in this volume of IEEE Std 1003.1-2001
does not cite this as an allowable case.
FUTURE DIRECTIONS
None.
SEE ALSO
awk , comm , sort , uniq
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
| IEEE/The Open Group | JOIN (P) | 2003 |
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