Simple directory watcher - allows you to monitor recursively a directory for changes in a file. Each time a changed is made, executes the comman that you specified

watcher.sh

#/bin/bash

##################################################################
# SIMPLE DIRECTORY WATCHER
#
# Usage:
#   bash test.sh
#
# Role:
# Simple Directory Watcher allows you to monitor
# recursively a directory for changes in a file
# each time a changed is made, execute a command
# that you specified.
#
# Parameters: (currently variables, someday arguments)
# - DIR_MONIT: The directory you want to monitor for changes.
# - COMMAND: The command to execute each time a change occurs.
# - TEMPO_IN_SECONDS: the time to wait in seconds between each scan
#   for changes.
#
# Version:
#   0.1
# Author:
#   Yann Feunteun
#   <[email protected]>
#
##################################################################


DIR_MONIT="/home/joe/some_java_project"
COMMAND="mvn package"
TEMPO_IN_SECONDS=2

# Beacuse I don't find a way to either use two shell
# within Emacs or use a Ctrl-c like to stop the process
# so to quit the program I use kill $(cat $PWD/pid.txt)
echo $$ > pid.txt

cd $DIR_MONIT && $COMMAND

# record last execution time to compare it to last changed time
# in DIR_MONIT
last_execution_time=$(date +%s)

while true
do 
    # Get the timestamp of the oldest file in the directory and
    # subdirectories of DIR_MONIT
    last_modified_time=$(find $DIR_MONIT 2> /dev/null  | xargs stat -c%Z | sort -n | tail -n 1)

    # Uncomment the following line to debug 
    #echo "Last modified time is $last_modified_time, last time command was executed is $last_execution_time"

    sleep $TEMPO_IN_SECONDS
    if [ $last_execution_time -lt $last_modified_time ]; then
	# Uncomment the following line to debug
	#echo "Command should be executed since file(s) has changed since last execution"
	cd $DIR_MONIT && $COMMAND
	last_execution_time=$(date +%s)
    fi
done