join [man page] - join lines of two files on a common field
join [OPTION]... FILE1 FILE2
equivalent to `-1 FIELD -2 FIELD'
join on this FIELD of file 1
join on this FIELD of file 2
Join command can be as a simple database join table.
Suppose that we have two following files, file1:
echo -e "0001 =\n0010 =\n0011 =\n0100 =\n0101\ =\n0111 =" | nl > file1
$ echo -e "one\ntwo\nthree\nfour\nfive\nsix" | nl > file2
now we can use join command to join those two files:
$ join -j 1 file1 file2