JOIN(1P) POSIX Programmer's Manual JOIN(1P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
join - relational database operator
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:
-a file_number
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.
-e string
Replace empty output fields in the list selected by -o with the
string string.
-o list
Construct the output line to comprise the fields specified in
list, each element of which shall have one of the following two
forms:
1. file_number.field, where file_number is a file number and
field is a decimal integer field number
2. 0 (zero), representing the join field
The elements of list shall be either comma-separated or <blank>-sepa-
rated, 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.
-t char
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.
-v file_number
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.
-1 field
Join on the fieldth field of file 1. Fields are decimal integers
starting with 1.
-2 field
Join on the fieldth field of file 2. Fields are decimal integers
starting with 1.
OPERANDS
The following operands shall be supported:
file1, file2
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.
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:
LANG 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 Vari-
ables for the precedence of internationalization variables used
to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all
the other internationalization variables.
LC_COLLATE
Determine the locale of the collating sequence join expects to
have been used when the input files were sorted.
LC_CTYPE
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).
LC_MESSAGES
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard error.
NLSPATH
Determine the location of message catalogs for the processing of
LC_MESSAGES .
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:
0 All input files were output successfully.
>0 An error occurred.
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 spe-
cific fields are identified using -o, join is not aware of what fields
might be empty. The exception to this is the join field, but identify-
ing 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-com-
patible 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 his-
torical 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 2003 JOIN(1P)
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