NAME
join —
relational database operator
SYNOPSIS
join |
[-1 field]
[-2 field]
[-a file_number |
-v file_number]
[-e string]
[-o list]
[-t char]
file1 file2 |
DESCRIPTION
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:
-1field- Join on the field'th field of file1.
-2field- Join on the field'th field of file2.
-afile_number- In addition to the default output, produce a line for each unpairable line in file file_number.
-estring- Replace empty output fields with string.
-olist- 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-ooptions.) -tchar- Use character char as a field delimiter for both input and output. Every occurrence of char in a line is significant.
-vfile_number- Do not display the default output, but display a line for each unpairable
line in file file_number. The options
-v1 and-v2 may be specified at the same time.
EXIT STATUS
The join utility exits 0 on
success, and >0 if an error occurs.
SEE ALSO
STANDARDS
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.
-jfield- Join on the field'th field of both file1 and file2.
-j1field- Join on the field'th field of file1.
-j2field- Join on the field'th field of file2.
-olist ...- Historical implementations of
joinpermitted multiple arguments to the-ooption. These arguments were of the form “file_number.field_number” as described for the current-ooption. 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.
HISTORY
A join utility appeared in
Version 7 AT&T UNIX.