File Comparison in Linux

Question

Could you please help me with the below requirement?

I have two files FILE1 and FILE2 with the below content (example):

FILE1:

Column1       Column2
------------------------
M             1.2
A             11
S             hostname
T             TCP
E             120
R             Y

FILE2:

Column1        Column2
---------------------------
A             12
M             1.3
T             SSL
S             hostname1

The order of fields in FILE1 and FILE2 are different, I want to compare FILE1 and FILE2, Take 1st column from FILE1 and search the entire column1 of FILE2 and once it finds the match, it has to pick column2 value (from FILE2) and replace the value in the corresponding field in FILE1.

Appreciate if someone can please help my requirement.

Answer 1

You could do something like:

$ join -o 0,1.2,2.2 -a 1 <(sort -k 1,1 FILE1) <(sort -k 1,1 FILE2) |
     awk '{print $1, $NF}'
A 12
E 120
M 1.3
R Y
S hostname1
T SSL

Or to preserve the order of the lines in FILE1:

$ awk '!n {a[$1] = $2; next}
   {print $1, $1 in a ? a[$1] : $2}' FILE2 n=1 FILE1
M 1.3
A 12
S hostname1
T SSL
E 120
R Y