join Join lines of two sorted files on a common field. Join two files on the first (default) field: join {{file1}} {{file2}} Join two files using a comma (instead of a space) as the field separator: join -t {{','}} {{file1}} {{file2}} Join field3 of file1 with field1 of file2: join -1 {{3}} -2 {{1}} {{file1}} {{file2}} Produce a line for each unpairable line for file1: join -a {{1}} {{file1}} {{file2}}