read numbers from one file and search for them in another using awk script

Question

I have 2 files, a.txt and b.txt, both of them are composed of numbers, one per line. What I'm trying to do is to read each number from a.txt, and search for it in b.txt. Here is the awk script file I wrote, I can execute this search.awk file like this,

awk -f search.awk a.txt 

but how to search for each number in b.txt?

#!/bin/awk -f

{
    print $1
    # how to search for $1 in b.txt?
}

UPDATE

What if there is not only 1 file to be searched, there are multiple files in a dir to be searched for each number in a.txt? I mean that, search all those files in a_dir/* for each number in a.txt?

Answer 1

Stash lines from a.txt into an array and print those lines from b.txt that occur in the array

awk 'NR == FNR{a[$0]; next} $0 in a' a.txt b.txt 

EDIT: If there are multiple files to be searched, this version prints the match file name and line

awk 'NR == FNR{a[$0]; next} $0 in a{print FILENAME, $0}' a.txt b.txt c.txt

Answer 2

Code example for awk:

awk 'NR==FNR {a[$1]=$1;next} $1==a[$1] && $1!=""' a.txt b.txt

---

$ cat a.txt
1
3
5
7
9
11
13

$ cat b.txt
1
4
7
10
13

$ cat c.txt
3
11

$ awk 'NR==FNR {a[$1]=$1;next} $1==a[$1] && $1!=""' a.txt b.txt c.txt
1
7
13
3
11