replace.sh

#!/bin/bash

search="$1"
replace="$2"
target_dir="$3"

[ -n "$search" ] || \
    { echo "search is empty"; exit 1; }
[ -n "$replace" ] || \
    { echo "replace is empty"; exit 1; }
[ -n "$target_dir" ] || \
    { echo "target_dir is empty"; exit 1; }
[ -d "$target_dir" ] || \
    { echo "\"$target_dir\" directory is missing"; exit 1; }

grep -rl "$search" "$target_dir" | \
    xargs sed -i "s/$search/$replace/g"