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

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

PROLOG         top

       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         top

       join — relational database operator

SYNOPSIS         top

       join [−a file_number|−v file_number] [−e string] [−o list] [−t char]
           [−1 field] [−2 field] file1 file2

DESCRIPTION         top

       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> 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         top

       The join utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, 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.1‐2008, 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         top

       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         top

       The standard input shall be used only if the file1 or file2 operand
       is '−'.  See the INPUT FILES section.

INPUT FILES         top

       The input files shall be text files.

ENVIRONMENT VARIABLES         top

       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.1‐2008, 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         top

       Default.

STDOUT         top

       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         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

        0    All input files were output successfully.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       Pathnames consisting of numeric digits or of the form string.string
       should not be specified directly following the −o list.

EXAMPLES         top

       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         top

       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 POSIX.1‐2008 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         top

       None.

SEE ALSO         top

       awk(1p), comm(1p), sort(1p), uniq(1p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                            JOIN(1P)