join
JOIN(1) General Commands Manual JOIN(1)
NAME
join – relational database operator
SYNOPSIS
join [-a file_number | -v file_number] [-e string] [-o list] [-t char]
[-1 field] [-2 field] 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. The following options are
available:
-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
The -o option specifies the fields that will be output from each
file for each line with matching join fields. Each element of list
has the either 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.
-1 field
Join on the field'th field of file 1.
-2 field
Join on the field'th field of file 2.
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.
EXIT STATUS
The join utility exits 0 on success, and >0 if an error occurs.
COMPATIBILITY
For compatibility with historic versions of join, the following options are
available:
-a In addition to the default output, produce a line for each
unpairable line in both file 1 and file 2.
-j1 field
Join on the field'th field of file 1.
-j2 field
Join on the field'th field of file 2.
-j field
Join on the field'th field of both file 1 and file 2.
-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 historic shell scripts do not require
modification. They should not be used in new code.
LEGACY DESCRIPTION
The -e option causes a specified string to be substituted into empty
fields, even if they are in the middle of a line. In legacy mode, the
substitution only takes place at the end of a line.
Only documented options are allowed. In legacy mode, some obsolete options
are re-written into current options.
For more information about legacy mode, see compat(5).
SEE ALSO
awk(1), comm(1), paste(1), sort(1), uniq(1), compat(5)
STANDARDS
The join command conforms to IEEE Std 1003.1-2001 (“POSIX.1”).
macOS 12.1 July 5, 2004 macOS 12.1