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.TH JOIN 1
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.CT 1 files
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.SH NAME
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join \- relational database operator
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.SH SYNOPSIS
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.B join
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[
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.I options
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]
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.I file1 file2
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.SH DESCRIPTION
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.I Join
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forms, on the standard output,
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a join
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of the two relations specified by the lines of
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.I file1
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and
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.IR file2 .
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If one of the file names is
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.LR - ,
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the standard input is used.
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.PP
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.I File1
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and
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.I file2
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must be sorted in increasing
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.SM UTF
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collating
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sequence on the fields
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on which they are to be joined,
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normally the first in each line.
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.PP
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There is one line in the output
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for each pair of lines in
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.I file1
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and
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.I file2
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that have identical join fields.
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The output line normally consists of the common field,
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then the rest of the line from
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.IR file1 ,
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then the rest of the line from
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.IR file2 .
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.PP
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Input fields are normally separated spaces or tabs;
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output fields by space.
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In this case, multiple separators count as one, and
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leading separators are discarded.
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.PP
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The following options are recognized, with POSIX syntax.
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.TF "\fL-j\fIn m\fR  "
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.PD
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.TP
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.BI -a " n
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In addition to the normal output,
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produce a line for each unpairable line in file
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.IR n ,
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where
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.I n
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is 1 or 2.
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.TP
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.BI -v " n
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Like
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.BR -a ,
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omitting output for paired lines.
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.TP
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.BI -e " s
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Replace empty output fields by string
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.IR s .
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.TP
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.BI -1 " m
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.br
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.ns
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.TP
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.BI -2 " m
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Join on the
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.IR m th
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field of
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.I file1
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or
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.IR file2 .
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.TP
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.BI -j "n m"
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Archaic equivalent for
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.BI - "n m\f1."
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.TP
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.BI -o fields
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Each output line comprises the designated fields.
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The comma-separated field designators are either
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.BR 0 ,
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meaning the join field, or have the form
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.IR n . m ,
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where
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.I n
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is a file number and
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.I m
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is a field number.
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Archaic usage allows separate arguments for field designators.
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.TP
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.BI -t c
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Use character
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.I c
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as the only separator (tab character) on input and output.
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Every appearance of
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.I c
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in a line is significant.
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.SH EXAMPLES
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.TP
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.L
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sort -t: +1 /adm/users | join -t: -1 2 -a 1 -e "" - bdays
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Add birthdays to the
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.B /adm/users
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file, leaving unknown
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birthdays empty.
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The layout of
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.B /adm/users
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is given in
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.IR users (6);
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.B bdays
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contains sorted lines like
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.LR "ken:Feb\ 4,\ 1953" .
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.TP
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.L
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awk -F: '$3 != ""' /adm/users | tr : ' ' | sort -k 3,3 >temp
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.br
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.ns
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.TP
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.L
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join -1 3 -2 3 -o 1.1,2.1 temp temp | awk '$1 < $2'
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Print all pairs of users with identical non-empty userids.
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.SH SOURCE
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.B /sys/src/cmd/join.c
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.SH "SEE ALSO"
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.IR sort (1),
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.IR comm (1),
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.IR awk (1)
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.SH BUGS
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With default field separation,
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the collating sequence is that of
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.BI "sort -b"
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.BI -k y , y\f1;
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with
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.BR -t ,
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the sequence is that of
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.BI "sort -t" x
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.BI -k y , y\f1.
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.PP
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One of the files must be randomly accessible.