Copying content of 2 files in a new file by pairing the values in linux

Question

There are supposed to be 2 files. One file has list of users and the other files has list of passwords. User file has 5 users and password file also has 5 passwords. What I have to do here is create a new file and pair each user with all the available passwords in password file. For example: user 1 is to be paired with password 1, 2,3,4,5. user 2 is to be paired with password 1,2,3,4,5 and so on.

My question is: 1. What loop should be used here? 2. My head says for pairing we need to use nested for loop. is it correct? 3. I can somehow imagine the 1st part of copying the contents but I'm not able to picture how to pair them. So I need help and suggestions.

EDIT:

Sample input are the 2 files named Username and Password.

Username file:

User1

User2

..

User5

Password file:

Pass1

Pass2

..

Pass5

Expected output is:

User1-Pass1

User1-Pass2

..

User1-Pass5

User2-Pass1

User2-Pass2

..

User2-Pass5

and so on till we reach User5-Pass5

Thanks.

Answer 1

Ad 1., 2. Yes, nested loop required.

Let's expect one user per line and one password per line, then code would be:

> concat  # delete file content
for usr in `cat file_with_users`
do  
    for pwd in `cat file_with_passwords`
    do
        echo "$usr-$pwd" >> result_file
    done 
done

If you write input sample and expected output, I can write something more specific.

Answer 2

always there is a better way

$ join -t, -j 99 users pwords | cut -d, -f2-

for example

$ echo u{1..5} | tr ' ' '\n' > users
$ echo p{1..5} | tr ' ' '\n' > pwords

$ join -t, -j 99 users pwords | cut -d, -f2-
u1,p1
u1,p2
u1,p3
u1,p4
u1,p5
u2,p1
u2,p2
...
u5,p4
u5,p5

for - delimiter change to join -t- -j 99 users pwords | cut -d- -f2- join -t- -j 99 users pwords | cut -d- -f2-

This is using a fictional column (99th) to create a join between each rows, which is called cross-product. Since the key is missing in the first position of the output we need to cut it out at the end.

Answer 3

Do either of these help:

grep -Fwf file1 file2 or 
awk 'NR==FNR{A[$1];next}$1 in A' file1 file2