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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> characters. In this
       case, multiple separators shall count as one field separator, and lead‐
       ing  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  out‐
		 put.  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 inte‐
		 gers starting with 1.

       −2 field	 Join on the fieldth field of file 2. Fields are decimal inte‐
		 gers 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 vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, 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>	 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:

	   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 pos‐
       sible 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 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  mul‐
       tiple  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 Electri‐
       cal  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.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			      JOIN(1P)
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