set -euo pipefail
export LC_ALL=C
grep_work=$(mktemp -d "${TMPDIR:-/tmp}/grep-example.XXXXXX")
trap 'rm -rf -- "$grep_work"' EXIT
cd "$grep_work"
mkdir -p data
cat > data/terms.txt <<'GRP_INPUT_1'
a+b
a.b
GRP_INPUT_1
cat > data/literals.txt <<'GRP_INPUT_2'
a+b
aaab
a.b
aXb
red blue
red  blue
home=$HOME
-error
GRP_INPUT_2

grep -Ff data/terms.txt data/literals.txt