join is a command in Unix and Unix-like operating systems that merges the lines of two sorted text files based on the presence of a common field.
The join command takes as input two text files and several options.
Both files have been sorted on the join field — this is a requirement of the program.
[1][2] The version of join bundled in GNU coreutils was written by Mike Haertel.
[3] The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.