join —
relational database operator
join |
[ -1
field
]
[-2
field
]
[-a
file_number |
-v
file_number
]
[-e
string
]
[-o
list
]
[-t
char
]
file1
file2 |
The
join utility performs an “equality
join” on the specified files and writes the result to the standard
output. The “join field” is the field in each file by which the
files are compared. The first field in each line is used by default. There is
one line in the output for each pair of lines in
file1 and
file2 which have identical join fields. Each
output line consists of the join field, the remaining fields from
file1 and then the remaining fields from
file2.
The default field separators are tab and space characters. In this case,
multiple tabs and spaces count as a single field separator, and leading tabs
and spaces are ignored. The default output field separator is a single space
character.
Many of the options use file and field numbers. Both file numbers and field
numbers are 1 based, i.e., the first file on the command line is file number 1
and the first field is field number 1.
When the default field delimiter characters are used, the files to be joined
should be ordered in the collating sequence of
sort(1), using the
-b option, on the fields on which they are
to be joined, otherwise
join may not report
all field matches. When the field delimiter characters are specified by the
-t option, the collating sequence should be
the same as
sort(1) without the
-b option.
If one of the arguments
file1 or
file2 is ‘-’, the standard
input is used.
The options are as follows:
-
-
-1
field- Join on the field'th field of
file1.
-
-
-2
field- Join on the field'th field of
file2.
-
-
-a
file_number- In addition to the default output, produce a line for each unpairable line
in file file_number.
-
-
-e
string- Replace empty output fields with
string.
-
-
-o
list- Specifies the fields that will be output from each file for each line with
matching join fields. Each element of
list has the form
“file_number.field”, where
file_number is a file number and
field is a field number, or the form
“0” (zero), representing the join field. The elements of
list must be either comma (‘
,’) or
whitespace separated. (The latter requires quoting to protect it from the
shell, or a simpler approach is to use multiple
-o options.)
-
-
-t
char- Use character char as a field delimiter
for both input and output. Every occurrence of
char in a line is significant.
-
-
-v
file_number- Do not display the default output, but display a line for each unpairable
line in file file_number. The options
-v 1
and -v
2 may be specified at the same
time.
The
join utility exits 0 on success,
and >0 if an error occurs.
awk(1),
comm(1),
lam(1),
paste(1),
sort(1),
uniq(1)
The
join utility is compliant with the
IEEE Std 1003.1-2008
(“POSIX.1”) specification.
In the absence of the
-o option, historical
versions of
join wrote non-matching lines
without reordering the fields. The current version writes the join field
first, followed by the remaining fields.
For compatibility with historical versions of
join, the following options are available:
-
-
-a- In addition to the default output, produce a line for each unpairable line
in both file1 and
file2.
-
-
-j
field- Join on the field'th field of both
file1 and
file2.
-
-
-j1
field- Join on the field'th field of
file1.
-
-
-j2
field- Join on the field'th field of
file2.
-
-
-o
list ...- Historical implementations of
join
permitted multiple arguments to the -o
option. These arguments were of the form
“file_number.field_number” as described for the current
-o option. This has obvious
difficulties in the presence of files named “1.2”.
These options are available only so historical shell scripts don't require
modification and should not be used.
A
join utility appeared in
Version 7 AT&T UNIX.
![[OpenBSD]](/openbsd.gif){kind=small}