Searching 100 files for "foo" (regex, case sensitive)

~/example.txt:
    1
    2: Hello foo
    4

~/example2.txt:
    1
    2: Hello world foo.
    3
    4: Hello world foo.
    5  Hello world.

~/example.txt:
    1
    2: Hello world.
    3

~/example2.txt:
    1
    2: Foo bar.
    3

~/example2.txt:
    1
    2: A b c...
    3

Hello world.

---

Foo bar.

---

A b c...

Hello world.

---

Foo world.

---

A b c...

~/example.txt:
    1
    2: Hello world.
    3

~/example2.txt:
    1
    2: Foo world.
    3

~/example2.txt:
    1
    2: A b c...
    3