基于Linux中的公共列合并两个不同长度的文件

Question

I would like to merge two files (file 1 & file 2) based on a common column to give (file 3). File 3 should have only the matched ids (mid) leaving out the mid=20 THE COMMON COLUMN HERE WOULD BE 'MID' AND THE MATCH IS BASED ON THAT COLUMN

I can do it with J command but the file 1 and file 2 are of different lenghts. Please suggest some ideas. Thanks in advance.

file 1

mid A1  A2  A3  A4  A5  A6
18  we  gf  32  23  45  89
19  ew  fg  33  24  46  90
21  ew  fg  35  26  48  92

file 2

mid B1  B2  B3  B4
18  r40 1   103 NA
19  r41 1   104 NA
20  r42 1   105 NA
21  r43 1   106 NA

file 3

mid B1  B2  B3  B4  A1  A2  A3  A4  A5  A6
18  r40 1   103 NA  we  gf  32  23  45  89
19  r41 1   104 NA  ew  fg  33  24  46  90
21  r43 1   106 NA  ew  fg  35  26  48  92

Answer 1

join正是针对此类任务而设计的：

join file2 file1