grep -rhi multiple strings from file

Question

Okay so I know i can do

grep -rhI "string1" .

but can I grab strings from a .txt file, so each string is on a new line, example

string1
string2
string3

as I have that many strings to process using

grep rhI "string1|string2|string3"

would be a pain..

Answer 1

Put all the strings in one file as this:

$ cat strings
string1
string2
string3

And execute:

$ grep -rhIoFf strings 

Edit

If it is not exactly string1 what you need as output (the effect of -o) keep reading

---

Convert the list of strings in file strings (if they do not have spaces or new lines) to one string separated with | :

filter=$(printf "%s|" $(cat strings))

Then, use the string as the filter for grep :

grep -rhIE "${filter%?}"