Relational database operator.
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.

      join [-a file_number | -v file_number]
              [-e string] [-j file_number field]
                 [-o list] [-t char] [-1 field] [-2 field] file1 file2

     -a file_number
                 In addition to the default output, produce a line for each
                 unpairable line in file file_number. (The argument to -a must
                 not be preceded by a space; see the COMPATIBILITY section.)

     -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 ele-
                 ment of list has the form `file_number.field', where
                 file_number is a file number and field is a field number.
                 The elements of list must be either comma (``,'') or whites-
                 pace separated.  (The latter requires quoting to protect it
                 from the shell, or, a simpler approach is to use multiple -o

     -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 can 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.

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.

"Work like you don't need the money, love like you've never been hurt, and dance like nobodys watching" ~ Satchel 'Satchmo' Paige

Related macOS commands

fmt - Reformat paragraph text.
fold - Wrap input lines to fit in specified width.
head - Output the first part of file(s).
split - Split a file into fixed-size pieces.
tail - Output the last part of files.

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