How to find if there are new files in a directory every 2 minutes in shell script?

Question

I have a directory called /home/user/local. Every two minutes or so, a new file is dumped into this directory. I need to check this directory every 2 minutes to see

Answer 1

First off a big thank you to leafei, I'd hoped that it was that easy. However for my devices writing temporary files for loops wasn't portable enough for my current project and I required performing actions for various things that might happen within a monitored directory, so here's the script I wrote based off leafei's answer and tested locally. Note formatting maybe off on first post...

#!/usr/bin/env bash
Var_monitor_dir="${1?No directory passed}"
Var_sleep_time="${2:-120}"
Var_diff_opts="--suppress-common-lines"
Func_parse_change(){
    _added_input="$(grep -E ">" <<<"${@}")"
    _removed_input="$(grep -E "<" <<<"${@}")"
    if [ "${#_added_input}" != "0" ]; then
            mapfile -t _arr_added <<<"${_added_input}"
            let _added_count=0
            until [ "${#_arr_removed}" = "${_added_count}" ]; do
                _current_path="${_arr_removed[${_added_count}]}"
                if [ -f "${_current_path}" ]; then
                    echo "# ${0##*/} detected added file: ${_current_path}"
                elif [ -d "${_current_path}" ]; then
                    echo "# ${0##*/} detected added directory ${_current_path}"
                elif [ -p "${_current_path}" ]; then
                    echo "# ${0##*/} detected added named pipe ${_current_path}"
                fi
                ## Ignore other added input and add to index counter
                let _added_count++
            done
            unset _added_count
    fi
    if [ "${#_removed_input}" != "0" ]; then
            mapfile -t _arr_removed <<<"${_added_input}"
            let _removal_count=0
            until [ "${#_arr_removed}" = "${_removal_count}" ]; do
                echo "# Removal detected: ${_arr_removed[${_removal_count}]}"
                let _removal_count++
            done
    fi
 }
 Func_watch_dir(){
    _current_listing=""
    while [ -d "${Var_monitor_dir}" ]; then
         _new_listing="$(ls "${Var_monitor_dir}")"
         _diff_listing="$(diff ${Var_diff_opts} <(echo "${_current_listing}") <(echo "${_new_listing}"))"
        if [ "${#_diff_listing}}" != "0" ]; then
            Func_parse_change "${_diff_listing}"
        fi
        _current_listing="${_new_listing}"
        sleep ${Var_sleep_time}
    done
}
if [ "${#@}" != "0" ]; then
     Func_watch_dir
     exit 0
else
     echo "${0##*/} needs a directory to monitor"
     exit 1
if

Assuming the above is saved as monitor_directory.sh and the directory to be monitored is /tmp then opening one terminal and inputting monitor_directory "/tmp" (or monitor_directory.sh "/tmp" "10" to have faster updates between tests) will start the loop that checks for changes. Then opening a second terminal try inputting the following and waiting for the first terminal to update

mkdir -p /tmp/test_dir
touch /tmp/test.file

After the wait time is up the first terminal should report that a file and a directory has appeared, if you run the following and wait again it'll show removals too.

rmdir /tmp/test_dir
rm /tmp/test.file

Hope this helps some.