#! /bin/sh

filter="$1"
src="$2"
dest="$3"

root="$(pwd)"

rm -r "$dest"
rsync -a --exclude '.*' "$src" "$dest"

files="$(find "$dest" -type f)"

for file in $files; do
    file "$file" | grep -q 'text' || continue
    cd "$(dirname "$file")" || exit 1

    file="$(basename "$file")"

    exec 3< "$file"
    rm "$file"

    sh -c "$filter" <&3 > "$file"

    exec 3>&-

    cd "$root"
done