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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>s. 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
       IEEE Std 1003.1-2001, 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>-sepa‐
       rated,  as  specified  in Guideline 8 of the Base Definitions volume of
       IEEE Std 1003.1-2001, 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
	      IEEE Std 1003.1-2001, 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>s), 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  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-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 IEEE Std 1003.1-2001 does not
       cite this as an allowable case.

FUTURE DIRECTIONS
       None.

SEE ALSO
       awk, comm, sort, uniq

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 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 .

IEEE/The Open Group		     2003			      JOIN(1P)
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