NAME

join − relational database operator

SYNOPSIS

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 collating sequence (see Environment Variables below) on the fields on which they are to be joined; normally the first in each line. 

The output contains one line for each pair of lines in file1 and file2 that have identical join fields.  The output line normally consists of the common field, followed by 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 of the below options use the argument n. This argument should be a 1 or a 2 referring to either file1 or file2, respectively. The following options are recognized:

−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.

−j n 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 c is used as the field separator for both input and output. 

−1 f Join on the fieldth field of file 1.  Fields are numbered starting with 1.

−2 f Join on the fieldth field of file 2.  Fields are numbered starting with 1.

EXAMPLE

The following command line joins 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.  It is assumed that the files have been sorted in the collating sequence defined by the LC_COLLATE or LANG environment variable on the group ID fields. 

join −1 4 −2 3 −o 1.1 2.1 1.6 −t: /etc/passwd /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 are incongruous. 

Filenames that are numeric may cause conflict when the -o option is used right before listing filenames. 

EXTERNAL INFLUENCES

Environment Variables

LC_COLLATE determines the collating sequence join expects from input files. 

LC_CTYPE determines the alternative blank character as an input field separator, and the interpretation of data within files as single and/or multi-byte characters.  LC_CTYPE also determines whether the separator defined through the −t option is a single- or multi-byte character. 

If LC_COLLATE or LC_CTYPE is not specified in the environment or is set to the empty string, the value of LANG is used as a default for each unspecified or empty variable.  If LANG is not specified or is set to the empty string, a default of “C” (see lang(5)) is used instead of LANG.  If any internationalization variable contains an invalid setting, join behaves as if all internationalization variables are set to “C” (see environ(5)).

International Code Set Support

Single- and multi-byte character code sets are supported with the exception that multi-byte character file names are not supported. 

STANDARDS CONFORMANCE

join: SVID2, XPG2, XPG3
 

Hewlett-Packard Company  —  HP-UX Release 7.0: Sept 1989