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JOIN(1)								       JOIN(1)

NAME
       join - relational database operator

SYNOPSIS
       join [ options ] file1 file2

DESCRIPTION
       Join  forms, on the standard output, a join of the two relations speci‐
       fied by the lines of file1 and file2.  If one of the file names is  the
       standard input is used.

       File1  and file2 must be sorted in increasing UTF collating sequence on
       the fields on which they are to be joined, normally the first  in  each
       line.

       There  is  one  line  in the output for each pair of lines in file1 and
       file2 that have identical join fields.  The output line	normally  con‐
       sists  of  the common field, then the rest of the line from file1, then
       the rest of the line from file2.

       Input fields are normally separated spaces or tabs;  output  fields  by
       space.	In  this  case,	 multiple separators count as one, and leading
       separators are discarded.

       The following options are recognized, with POSIX syntax.

       -a n   In addition to the  normal  output,  produce  a  line  for  each
	      unpairable line in file n, where n is 1 or 2.

       -v n   Like -a, omitting output for paired lines.

       -e s   Replace empty output fields by string s.

       -1 m
       -2 m   Join on the mth field of file1 or file2.

       -jn m  Archaic equivalent for -n m.

       -ofields
	      Each  output  line  comprises the designated fields.  The comma-
	      separated field designators  are	either	0,  meaning  the  join
	      field, or have the form n.m, where n is a file number and m is a
	      field number.  Archaic usage allows separate arguments for field
	      designators.

       -tc    Use  character  c as the only separator (tab character) on input
	      and output.  Every appearance of c in a line is significant.

EXAMPLES
       sort -t: +1 /adm/users | join -t: -1 2 -a 1 -e "" - bdays
	      Add birthdays to the /adm/users file, leaving unknown  birthdays
	      empty.   The  layout  of	/adm/users is given in users(6); bdays
	      contains sorted lines like

       awk -F: '$3 != ""' /adm/users | tr : ' ' | sort -k 3,3 >temp
       join -1 3 -2 3 -o 1.1,2.1 temp temp | awk '$1 < $2'
	      Print all pairs of users with identical non-empty userids.

SOURCE
       /sys/src/cmd/join.c

SEE ALSO
       sort(1), comm(1), awk(1)

BUGS
       With default field separation, the collating sequence is that  of  sort
       -b -ky,y; with -t, the sequence is that of sort -tx -ky,y.

       One of the files must be randomly accessible.

								       JOIN(1)
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