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

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(P)
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