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 correspond-
       ing 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>-separated, 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  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
", <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
", <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 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 paral-
       lel 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 Technol-
       ogy -- 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)