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	join.1 - 9base - revived minimalist port of Plan 9 userland to Unix
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	join.1 (2557B)
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	1 .TH JOIN 1
	2 .CT 1 files
	3 .SH NAME
	4 join \- relational database operator
	5 .SH SYNOPSIS
	6 .B join
	7 [
	8 .I options
	9 ]
	10 .I file1 file2
	11 .SH DESCRIPTION
	12 .I Join
	13 forms, on the standard output,
	14 a join
	15 of the two relations specified by the lines of
	16 .I file1
	17 and
	18 .IR file2 .
	19 If one of the file names is
	20 .LR - ,
	21 the standard input is used.
	22 .PP
	23 .I File1
	24 and
	25 .I file2
	26 must be sorted in increasing
	27 .SM ASCII
	28 collating
	29 sequence on the fields
	30 on which they are to be joined,
	31 normally the first in each line.
	32 .PP
	33 There is one line in the output
	34 for each pair of lines in
	35 .I file1
	36 and
	37 .I file2
	38 that have identical join fields.
	39 The output line normally consists of the common field,
	40 then the rest of the line from
	41 .IR file1 ,
	42 then the rest of the line from
	43 .IR file2 .
	44 .PP
	45 Input fields are normally separated spaces or tabs;
	46 output fields by space.
	47 In this case, multiple separators count as one, and
	48 leading separators are discarded.
	49 .PP
	50 The following options are recognized, with POSIX syntax.
	51 .TP
	52 .BI -a " n
	53 In addition to the normal output,
	54 produce a line for each unpairable line in file
	55 .IR n ,
	56 where
	57 .I n
	58 is 1 or 2.
	59 .TP
	60 .BI -v " n
	61 Like
	62 .BR -a ,
	63 omitting output for paired lines.
	64 .TP
	65 .BI -e " s
	66 Replace empty output fields by string
	67 .IR s .
	68 .TP
	69 .BI -1 " m
	70 .br
	71 .ns
	72 .TP
	73 .BI -2 " m
	74 Join on the
	75 .IR m th
	76 field of
	77 .I file1
	78 or
	79 .IR file2 .
	80 .TP
	81 .BI -j "n m"
	82 Archaic equivalent for
	83 .BI - n " m"\f1.
	84 .TP
	85 .BI -o fields
	86 Each output line comprises the designated fields.
	87 The comma-separated field designators are either
	88 .BR 0 ,
	89 meaning the join field, or have the form
	90 .IR n . m ,
	91 where
	92 .I n
	93 is a file number and
	94 .I m
	95 is a field number.
	96 Archaic usage allows separate arguments for field designators.
	97 .PP
	98 .TP
	99 .BI -t c
	100 Use character
	101 .I c
	102 as the only separator (tab character) on input and output.
	103 Every appearance of
	104 .I c
	105 in a line is significant.
	106 .SH EXAMPLES
	107 .TP
	108 .L
	109 sort /etc/passwd \| join -t: -1 1 -a 1 -e "" - bdays
	110 Add birthdays to the
	111 .B /etc/passwd
	112 file, leaving unknown
	113 birthdays empty.
	114 The layout of
	115 .B /adm/users
	116 is given in
	117 .IR passwd (5);
	118 .B bdays
	119 contains sorted lines like
	120 .LR "ken:Feb\ 4,\ 1953" .
	121 .TP
	122 .L
	123 tr : ' ' </etc/passwd \| sort -k 3 3 >temp
	124 .br
	125 .ns
	126 .TP
	127 .L
	128 join -1 3 -2 3 -o 1.1,2.1 temp temp \| awk '$1 < $2'
	129 Print all pairs of users with identical userids.
	130 .SH SOURCE
	131 .B \*9/src/cmd/join.c
	132 .SH "SEE ALSO"
	133 .IR sort (1),
	134 .IR comm (1),
	135 .IR awk (1)
	136 .SH BUGS
	137 With default field separation,
	138 the collating sequence is that of
	139 .BI "sort -b"
	140 .BI -k y , y\f1;
	141 with
	142 .BR -t ,
	143 the sequence is that of
	144 .BI "sort -t" x
	145 .BI -k y , y\f1.
	146 .PP
	147 One of the files must be randomly accessible.