Here is the text files we have:


4 9
5 8


1 2 3 5 8 9 5 3 3 2 4
4 7 8 9 5 6 8 9 0 8 7
7 8 0 7 4 7 7 9 0 6 7
2 7 9 5 7 9 0 7 6 5 4

I want extract the two columns (H and N) from file2.txt when A column in file1.txt matches with the L column in file2.txt, and the output text file to be shown should be like this:


4 9 7 7
5 8 4 8

How can I do that?

closed as unclear what you're asking by Sparhawk, RalfFriedl, Kiwy, jimmij, Romeo Ninov Sep 12 '18 at 6:03

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    always add the input and expected output in text format. everyone cannot see the attached image – Kamaraj Sep 11 '18 at 4:12
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    How would column A in file1.txt ever match with column L in file2.txt when the columns in file1.txt have three fields and the columns in file2.txt have five fields? Furthermore, your output doesn't show columns H and N extracted extracted from file2.txt but just colums A and B from file1.txt with some numbers just placed into columns C and D from file1.txt. Lastly, what have you tried to get the output that you want? – Nasir Riley Sep 11 '18 at 4:43
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    This task is rather hard to do using typical Linux command line tools. I would rather recommend writing a script/program. – Hubert Grzeskowiak Sep 11 '18 at 6:01
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    Could you share with us what you've try ? it look a lot like homework... Question on Unix&Linux should show proof of work... we are not freelancers – Kiwy Sep 11 '18 at 12:52

Not possible using grep, but doable using awk:

$ awk 'NR==1   {print $0;next}              # Print header
       NR==FNR {a[$1]=$2;next}              # collect data from file1.txt
               { if($5 in a)                # If column L match
                 { print($5,a[$5],$1,$7) }  # print columns (H and N)
      ' file1.txt file2.txt

As a one-liner:

$ awk 'NR==1{print $0;next} NR==FNR{a[$1]=$2;next} {if($5 in a){print($5,a[$5],$1,$7)}}' file1.txt file2.txt

5 8 4 8
4 9 7 7

The order is as the fields appear in the file2.txt.
If you need that sorted, then add a sort step.

  • Thank you so much. I solved the problem already. But I have one more question to ask, if the situation change to column L include some wordings in column A instead of completely matched, how would the code if($5 in a) change? – Owen Sep 12 '18 at 9:36
  • @Owen Situation? Wordings? .... Hmmm .... Those are very generic descriptions, it is impossible for me to make a reasonable guess of what you may mean. I would recommend to open a new question with a clear description of what you need. – Isaac Sep 13 '18 at 1:44

I would go with a step by step approach, to explain

  1. Sort the file 1

    sort file1.txt > file1.sorted.txt

  2. Take the interesting portion out from file2 (and sort it too)

    awk '{print $5,$1,$7}' file2.txt | sort > file2_of_interest.txt

  3. Join the two outputs based on the key, which is column 1 in both the files

    join file1.sorted.txt file2_of_interest.txt -1 1 -2 1

You can combine the three steps using indirection - but in the end you would need to complete parse at least one file. There would also be concerns on cases where column L in file2.txt is not unique and/or column 1 in file1.txt is not unique - you would need to resolve those by putting in your business logic to make the key unique.

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