What is the command to enter for filtering in Linux?

Question

linux

Hello!
There are 2 files file A and file B
Contents of file A:

id1:441
id2:458
id3:456
id4:233

B file content:

id1
id2

What command should be done in the Linux terminal in order to display only the lines:

id1:441
id2:458

Answer 1

fgrep -f {B,A}.txt

Answer 2

cat A.txt | egrep "^id\d:\d+"

Answer 3

I'm not sure that I understood the problem correctly, but I'll make an assumption:

cat fileA | egrep "id1|id2"
id1:441
id2:458

Answer 4

cat A.txt | grep -f B.txt

Answer 5

while read;do grep $REPLY A;done<B

Answer 6

join --nocheck-order -t : ./B ./A