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I have two files

file1:

45 789 
46 4546
78 4564
71 546

file2:

41 456 
46 456
40 465
45 456

I would like to compare these files and get an output: if the number in first column from first file is in the first column of the second file print a row from second file that include this number.

Desired output:

46 456
45 456

It will be something with grep? Thank you very much

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2

Read the first file's column to populate an array of "seen" values. Then when reading the second file, if the first value has been "seen", print the record:

$ awk 'NR == FNR { data[$1] = 1 } NR != FNR && data[$1] { print }' file1 file2
46 456
45 456

Rather than using the FR == NR and FR != NR tests, we could also use FILENAME == "file1" and FILENAME == "file2".

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  • Thank you very much and what is the difference of these solutions? – Lukáš Altman Apr 23 '19 at 19:53
  • The difference is that the solution given will work on any number of subsequent files beyond the first two; hard-coding the file names will only work on two files with the specific names given. Comparing NR and FNR is a simple "is this the first file or literally any other file" test. – DopeGhoti Apr 23 '19 at 19:56
  • Thank you for your help – Lukáš Altman Apr 24 '19 at 2:40
1

Assuming your shell is bash/ksh/zsh:

join -o 0,2.2 <(sort file1) <(sort file2)
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1

command

awk 'NR==FNR{a[$1];next}($1 in a){print $0}' file1 file2

output

46 456
45 456
| improve this answer | |
  • This code-only answer would be much improved if you explained what and how the awk code is doing. – Anthony Geoghegan Apr 24 '19 at 10:53
  • This works much like the currently accepted answer; the main difference is that it "short circuits" after filling the "seen values" array rather than testing for inequality of NR and FNR. – DopeGhoti Apr 24 '19 at 16:05

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