Inotify itself is a kernel module accesible via calls from e.g. a C program.
https://linux.die.net/man/7/inotify
There is an application suite called inotify-tools, which contains:
inotifywait – wait for changes to files using inotify
and
inotifywatch – gather filesystem access statistics using inotify
You can use inotify directly from command line, e.g. like this to continuously monitor for all changes under home directory (may generate lots of output):
inotifywait -r -m $HOME
And here is a script that monitors continuously and reacts to Apache log activity, copied from the man file of inotifywait:
#!/bin/sh
while inotifywait -e modify /var/log/messages; do
if tail -n1 /var/log/messages | grep httpd; then
kdialog --msgbox "Apache needs love!"
fi
done