Join (Unix)

Overview

The join command takes as input two text files and several options. If no command-line argument is given, this command looks for a pair of lines from the two files having the same first field (a sequence of characters that are different from space), and outputs a line composed of the first field followed by the rest of the two lines.

The program arguments specify which character to be used in place of space to separate the fields of the line, which field to use when looking for matching lines, and whether to output lines that do not match. The output can be stored to another file rather than printed using redirection.

As an example, the two following files list the known fathers and the mothers of some people. Both files have been sorted on the join field — this is a requirement of the program.

george jim kumar gunaware

albert martha george sophie

The join of these two files (with no argument) would produce:

george jim sophie

Indeed, only "george" is common as a first word of both files.