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       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
       sortb  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.1‐2008, 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

       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.1‐2008,  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

       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.

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:

           joint "<tab>"a 1a 2e '(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 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

       None.

SEE ALSO

       awk, comm, sort, uniq

       The Base Definitions volume of  POSIX.1‐2008,  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, 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 .