JOIN(1)                    POSIX Programmer's Manual                   JOIN(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 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.

OPTIONS
       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 --aa1 and --aa2 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 --vv1 and --vv2 are specified, all unpairable lines shall
                 be output.

       --11 field  Join on the fieldth field of file 1. Fields are decimal
                 integers starting with 1.

       --22 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 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.

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> characters), 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.

       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.

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

       (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

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 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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       awk, comm, sort, uniq

       The Base Definitions volume of POSIX.1-2017, Section 7.3.2, LC__COLLATE,
       Chapter _8, Environment Variables, Section 12.2, Utility Syntax
       Guidelines

COPYRIGHT
       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(1)
