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PROLOG | NAME | 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 |
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JOIN(1P) POSIX Programmer's Manual JOIN(1P)
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.
join — relational database operator
join [-a file_number|-v file_number] [-e string] [-o list] [-t char]
[-1 field] [-2 field] file1 file2
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 join fields that
collate equally. 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> characters.
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.
The join utility shall conform to the Base Definitions volume of
POSIX.1‐2017, 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>-separated, as specified in Guideline 8 of
the Base Definitions volume of POSIX.1‐2017, 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.
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.
The standard input shall be used only if the file1 or file2
operand is '-'. See the INPUT FILES section.
The input files shall be text files.
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 POSIX.1‐2017, Section 8.2,
Internationalization Variables 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.
Default.
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> characters), a single <space> shall be written
after each field (except the last).
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 All input files were output successfully.
>0 An error occurred.
Default.
The following sections are informative.
Pathnames consisting of numeric digits or of the form
string.string should not be specified directly following the -o
list.
If the collating sequence of the current locale does not have a
total ordering of all characters (see the Base Definitions volume
of POSIX.1‐2017, Section 7.3.2, LC_COLLATE), join treats fields
that collate equally but are not identical as being the same. If
this behavior is not desired, it can be avoided by forcing the
use of the POSIX locale (although this means re-sorting the input
files into the POSIX locale collating sequence.)
When using join to process pathnames, it is recommended that
LC_ALL, or at least LC_CTYPE and LC_COLLATE, are set to POSIX or
C in the environment, since pathnames can contain byte sequences
that do not form valid characters in some locales, in which case
the utility's behavior would be undefined. In the POSIX locale
each byte is a valid single-byte character, and therefore this
problem is avoided.
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
(where <tab> is a literal <tab> character) 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
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 for IEEE Std 1003.2‐1992 did 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 for IEEE Std 1003.2‐1992. 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 POSIX.1‐2017 does
not cite this as an allowable case.
Earlier versions of this standard allowed -j, -j1, -j2 options,
and a form of the -o option that allowed the list option-argument
to be multiple arguments. These forms are no longer specified by
POSIX.1‐2008 but may be present in some implementations.
None.
awk(1p), comm(1p), sort(1p), uniq(1p)
The Base Definitions volume of POSIX.1‐2017, Section 7.3.2,
LC_COLLATE, Chapter 8, Environment Variables, Section 12.2,
Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 JOIN(1P)
Pages that refer to this page: sort(1p)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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