join(1)
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join Command
relational database operator
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SYNTAX
join [ options ] file1 file2
DESCRIPTION
Join forms, on the standard output, a join of the two relations
specified by the lines of file1 and file2. If file1 is -, the
standard input is used.
File1 and file2 must be sorted in increasing ASCII 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 consists of the common field, then the rest of the line
from file1, then the rest of the line from file2.
The default input field separators are blank, tab, or new-line.
In this case, multiple separators count as one field separator,
and leading separators are ignored. The default output field
separator is a blank.
Some options use the argument n. This argument should be a 1 or
a 2 referring to either file1 or file2, respectively. Options
are:
-an In addition to the normal output, produce a line for
each unpairable line in file n, where n is 1 or 2.
-e s Replace empty output fields by string s.
-jn m Join on the mth field of file n. If n is missing, use
the mth field in each file. Fields are numbered
starting with 1.
-o list Each output line comprises the fields specified in list,
each element of which has the form n.m, where n is a
file number and m is a field number. The common field
is not printed unless specifically requested.
-tc Use character c as a separator (tab character). Every
appearance of c in a line is significant. The character
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join(1)
c is used as the field separator for both input and
output.
EXAMPLE
The following command lines sort the passwd and group file on the
key fields and join the password file and the group file,
matching on the numeric group ID, and outputting the login name,
the group name and the login directory.
$ sort +3 -4 -t: /etc/passwd >/tmp/passwd.sort
$ sort +2 -3 -t: /etc/group >/tmp/group.sort
$ join -j1 4 -j2 3 -o 1.1 2.1 1.6 -t:/tmp/passwd.sort/tmp/etc.group
SEE ALSO
awk(1), comm(1), sort(1), uniq(1).
BUGS
With default field separation, the collating sequence is that of
sort -b; with -t, the sequence is that of a plain sort.
The conventions of join, sort, comm, uniq and awk(1) are wildly
incongruous.
Numeric filenames may cause conflict when the -o option is used
right before listing filenames.
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