Bash Script to Monitor Directory Changes Using inotifywait

Use inotifywait -m /path/to/dir in a Bash script to monitor directory changes continuously and print events as they happen.

Examples

InputMonitor /tmp directory

OutputSetting up monitoring on /tmp Event detected: MODIFY file.txt

InputMonitor /home/user/docs directory

OutputSetting up monitoring on /home/user/docs Event detected: CREATE newfile.txt

InputMonitor empty directory /emptydir

OutputSetting up monitoring on /emptydir (No events until a change occurs)

How to Think About It

To monitor directory changes, the script uses a tool that listens for file system events like creation, deletion, or modification. It waits and prints these events as they happen, so you can see changes live.

Algorithm

1

Get the directory path to monitor as input

2

Use a system tool to watch for file system events in that directory

3

Print each event as it occurs

4

Keep running to continuously monitor changes

Code

bash

#!/bin/bash

DIR_TO_WATCH="$1"

if [ -z "$DIR_TO_WATCH" ]; then
  echo "Usage: $0 /path/to/directory"
  exit 1
fi

if ! command -v inotifywait &> /dev/null; then
  echo "Please install inotify-tools package to use this script."
  exit 1
fi

echo "Monitoring directory: $DIR_TO_WATCH"
inotifywait -m -e create -e modify -e delete "$DIR_TO_WATCH" | while read path action file; do
  echo "Event detected: $action $file"
done

Output

Monitoring directory: /tmp
Event detected: CREATE example.txt
Event detected: MODIFY example.txt
Event detected: DELETE example.txt

Dry Run

Let's trace monitoring /tmp directory with a file creation event

1

Start script with directory /tmp

DIR_TO_WATCH=/tmp

2

Check if inotifywait is installed

inotifywait found

3

Start monitoring /tmp

Waiting for events...

4

File example.txt created

Output: Event detected: CREATE example.txt

Step	Action	Output
1	Set DIR_TO_WATCH=/tmp
2	Check inotifywait	Found
3	Start monitoring	Waiting for events
4	File created	Event detected: CREATE example.txt

Why This Works

Step 1: Using inotifywait

The script uses inotifywait which listens to file system events in real time.

Step 2: Monitoring specific events

It watches for create, modify, and delete events to catch common changes.

Step 3: Continuous monitoring

The -m flag keeps the command running to report events as they happen.

Alternative Approaches

Polling with ls and sleep

bash

#!/bin/bash
DIR="$1"
PREV=$(ls "$DIR")
while true; do
  sleep 2
  CURR=$(ls "$DIR")
  if [ "$PREV" != "$CURR" ]; then
    echo "Change detected in $DIR"
    PREV="$CURR"
  fi
done

Simple but inefficient; checks directory contents every 2 seconds instead of event-driven.

Using fswatch tool

bash

#!/bin/bash
fswatch -0 "$1" | while read -d "" event; do
  echo "Change detected: $event"
done

Requires fswatch installed; works on multiple platforms but less common than inotifywait on Linux.

Complexity: O(1) per event time, O(1) space

Time Complexity

The script waits for events and processes each as it occurs, so time per event is constant.

Space Complexity

Uses minimal memory to store event info and directory path; no large data structures.

Which Approach is Fastest?

Using inotifywait is fastest and most efficient compared to polling or other tools.

Approach	Time	Space	Best For
inotifywait	O(1) per event	O(1)	Real-time, efficient monitoring
Polling with ls	O(n) every interval	O(n)	Simple but inefficient, cross-platform
fswatch	O(1) per event	O(1)	Cross-platform, requires extra tool