Loop through contents of txt file to find match in 2nd txt file (Mac OS or Linux)

Question

Searched the site and couldn't find what I need. I have two .txt files, each with a single value on each line separated by a linebreak.

1st TXT File	2nd TXT File
value1	value3
value2	value4
value3	value5
...	value6
...	value7
...	value8

In Mac OS or Linux, how do I loop through every line of the 1st .txt file and find a corresponding value in the 2nd .txt file? Ideally, I'd like to output a final.txt that only shows the values that were found.

Any help is appreciated! Thank you in advance!

Answer 1

grep -o -f 1sttxtfile 2ndtxtfile >  final.txt

Use the contents of the first file as search terms to find in the second file by using the -f flag. Print only the matches with -o