Watch a directory + execute a command on update

watch.sh

#!/bin/bash
#
# This script will watch a directory, and execute an arbitrary
# command when there is a change to a file within it.
#
# @param $1: The directory to watch for any changes
# @param $2: The command to run when there is a change
##################################################

current_md5=""
previous_md5=""

traverse_directory() {
    for file in $(ls $1); do
        local file_path="$1/$file"
        if [[ -f "$file_path" ]]; then
            current_md5+=$(md5 "$file_path")
        else
            traverse_directory "$file_path"
        fi
    done
}

while true; do
    traverse_directory "$1"
    if [[ $previous_md5 != "" ]]; then
        if [[ "$current_md5" != "$previous_md5" ]]; then
            $2
        fi
    fi
    previous_md5="$current_md5"
    current_md5=""
    sleep .5
done