macos - Bash script, watch folder, execute command

Question

I am trying to create a bash script with 2 parameters:

• a directory
• a command.

I want to watch the directory parameter for changes: when something has been changed the script should execute the command.

I'm running MacOS, not Linux; any pointers or external resources would greatly help as I have see that this is difficult to achieve. Really OI am trying to mimic SASS's watch functionality.

#!/bin/bash

#./watch.sh $PATH $COMMAND

DIR=$1  

ls -l $DIR > $DIR/.begin
#this does not work
DIFFERENCE=$(diff .begin .end)

if [ $DIFFERENCE = '
']; then
    #files are same
else
    $2
fi 

ls -l $DIR > $DIR/.end

Answer 1

To continuously recursively monitor folder (md5) and execute a command on change:

daemon() {
    chsum1=""

    while [[ true ]]
    do
        chsum2=`find src/ -type f -exec md5 {} ;`
        if [[ $chsum1 != $chsum2 ]] ; then           
            if [ -n "$chsum1" ]; then
                compile
            fi
            chsum1=$chsum2
        fi
        sleep 2
    done
}

Works on my OS X as I do not have digest.

On Linux, you can use md5sum as a replacement for the md5 command.