join – relational database operator|
join [ options ] file1 file2|
Join forms, on the standard output, a join of the two relations
specified 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 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.
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.
−2 m Join on the mth field of file1 or file2.
−jn mArchaic equivalent for −n m.
−tc Use character c as the only separator (tab character) on input
and output. Every appearance of c in a line is significant.
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.
sort /etc/passwd | join −t: −1 1 −a 1 −e "" − bdays|
tr : ' ' </etc/passwd | sort −k 3 3 >temp
Add birthdays to the /etc/passwd file, leaving unknown birthdays
empty. The layout of /adm/users is given in passwd(5); bdays contains
sorted lines like ken:Feb 4, 1953.|
join −1 3 −2 3 −o 1.1,2.1 temp temp | awk '$1 < $2'
Print all pairs of users with identical userids.|
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.|