Extract lines from File2 already found File1

Using linux commandline, i need to output the lines from text file2 that are already found in file1.

File1:

C
A
G
E
B
D
H
F

File2:

N
I
H
J
K
M
D
L
A

Output:

A
D
H

Thanks!

Answer

A more flexible tool to use would be awk

awk 'NR==FNR{lines[$0]++; next} $1 in lines'

Example

$ awk 'NR==FNR{lines[$0]++; next} $1 in lines' file1 file2
H
D
A

What it does?

• NR==FNR{lines[$0]++; next}

  • NR==FNR checks if the file number of records is equal to the overall number of records. This is true only for the first file, file1

  • lines[$0]++ Here we create an associative array with the line, $0 in file 1 as index.

• $0 in lines This line works only for the second file because of the next in previous action. This checks if the line in file 2 is there in the saved array lines, if yes the default action of printing the entire line is taken

---

Awk is more flexible than the grep as you can columns in file1 with any column in file 2 and decides to print any column rather than printing the entire line