join: Join lines on a common field
join writes to standard output a line for each pair of input
lines that have identical join fields. Synopsis:
join [option]… file1 file2
Either file1 or file2 (but not both) can be ‘-’, meaning standard input. file1 and file2 should be sorted on the join fields.
$ cat file1 a 1 b 2 e 5 $ cat file2 a X e Y f Z $ join file1 file2 a 1 X e 5 Y
join’s default behavior (when no options are given):