How to grep multiple lines from a file in linux

Question

I have a file with the below content.

.
.
hello
.
.
.
world
.
.
hello
.
.
.
.
.
world
.
.

the dots indicates the other lines in the file. Here what I need to gerp only the lines hello and world. That means the output should something like below.

hello
world
hello
world

How to accomplish this ?

Thanks,

Solution 1

Using grep:

grep -E 'hello|world' file

Using awk:

awk '/hello|world/' file

Solution 2

You can use grep with the -x option to match whole line and (Extended) Regex operator, |, to perform a logical OR between patterns:

grep -xE 'hello|world' file.txt

If your grep doesn't support the -E option, use Basic Regex with escaped |:

grep -x 'hello\|world' file.txt

---

Additionally, if you can't use the -x option to match the whole line, use Regex operators:

grep -E '^(hello|world)$' file.txt