Join is a convenient text processor provided by Linux or other Unix-like systems. Join is for two files with a common field. Thus, joining two files are pretty straight forward:
join FILE1 FILE2
However, joining three files become non-trivial especially when you join on a field other than the first field. For example, in order to join as to the second field of files, you may try as follows:
join -j 2 FILE1 FILE2 | join -j 2 - FILE3
The result would be an error because the output from the first join changes the position of the common field. So, your second join should be:
join -j 2 FILE1 FILE2 | join -1 1 -2 2 - FILE3
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