Bash shell script that watches a file and executes a command if the file changes.

watch.sh

#!/bin/sh
# Shell script that watches a file and executes a command if the file changes.

# Matt Taylor
# http://blog.matthewjosephtaylor.com
# License: This is free and unencumbered software released into the public domain.
# Thanks to code/tips from some helpful souls on irc.freenode.net ##unix
# All errors are of course my own. :)


#BSD Based Unix (Mac OSX)
STAT_FILE_MOD_PARAM="%m"

#SVR4 Based Unix (Linux)
#STAT_FILE_MOD_PARAM="%y"

function usage {
	echo "usage: $(basename $0) file command [command parameters ...]"
	exit
}

if [ $# -lt "2" ]
then
	usage
fi

THE_FILE=$1; shift
THE_COMMAND=$@; 

function get_mod {
	local result=$(stat -f "${STAT_FILE_MOD_PARAM}" ${THE_FILE})
	echo "$result"
	
}

last_mod=$(get_mod)

function test_modified {
	local current_mod=$(get_mod)
	if [ "$current_mod" != "$last_mod" ]
	then
		$THE_COMMAND
		#echo $current_mod
		#echo $last_mod
	fi
	last_mod=$current_mod
}

while true; do
	sleep 1
	test_modified
done